- Email: [email protected]
Nudiviruses and other large, double-stranded circular DNA viruses of invertebrates: New insights on an old topic
Journal of Invertebrate Pathology 101 (2009) 187–193
Contents lists available at ScienceDirect
Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/yjipa
Nudiviruses and other large, double-stranded circular DNA viruses of invertebrates: New insights on an old topic Yongjie Wang *, Johannes A. Jehle * Laboratory for Biotechnological Crop Protection, Department of Phytopathology, Agricultural Service Center Palatinate (DLR Rheinpfalz), Breitenweg 71, 67435, Neustadt a.d. Weinstrasse, Germany
a r t i c l e
i n f o
Article history: Received 6 March 2009 Accepted 9 March 2009 Available online 19 May 2009 Keywords: Nudiviruses Baculoviruses Monodon Baculovirus Salivary gland hypertrophy virus White spot syndrome virus Large DNA viruses Genome Evolution Phylogeny Classification
a b s t r a c t Nudiviruses (NVs) are a highly diverse group of large, circular dsDNA viruses pathogenic for invertebrates. They have rod-shaped and enveloped nucleocapsids, replicate in the nucleus of infected host cells, and possess interesting biological and molecular properties. The unassigned viral genus Nudivirus has been proposed for classification of nudiviruses. Currently, the nudiviruses comprise five different viruses: the palm rhinoceros beetle virus (Oryctes rhinoceros NV, OrNV), the Hz-1 virus (Heliothis zea NV-1, HzNV1), the cricket virus (Gryllus bimaculatus NV, GbNV), the corn earworm moth Hz-2 virus (HzNV-2), and the occluded shrimp Monodon Baculovirus reassigned as Penaeus monodon NV (PmNV). Thus far, the genomes of OrNV, GbNV, HzNV-1 and HzNV-2 have been completely sequenced. They vary between 97 and 230 kbp in size and encode between 98 and 160 open reading frames (ORFs). All sequenced nudiviruses have 33 ORFs in common. Strikingly, 20 of them are homologous to baculovirus core genes involved in RNA transcription, DNA replication, virion structural components and other functions. Another nine conserved ORFs are likely associated with DNA replication, repair and recombination, and nucleotide metabolism; one is homologous to baculovirus iap-3 gene; two are nudivirus-specific ORFs of unknown function. Interestingly, one nudivirus ORF is similar to polh/gran gene, encoding occlusion body protein matrix and being conserved in Alpha- Beta- and Gammabaculoviruses. Members of nudiviruses are closely related and form a monophyletic group consisting of two sister clades of OrNV/ GbNV and HzNVs/PmNV. It is proposed that nudiviruses and baculoviruses derived from a common ancestor and are evolutionarily related to other large DNA viruses such as the insect-specific salivary gland hypertrophy virus (SGHV) and the marine white spot syndrome virus (WSSV). Ó 2009 Elsevier Inc. All rights reserved.
1. Introduction Nudiviruses (Latin nudi = bare, naked, uncovered) comprise a diverse group of large double-stranded (ds) DNA viruses pathogenic for aquatic and terrestrial invertebrates. Like insect-specific baculoviruses (Rohrmann, 2008), they have rod-shaped and enveloped nucleocapsids and replicate in the nucleus of infected host cells resulting in nuclear hypertrophy (Burand, 1998). Nudiviruses (NVs) are considered to be potential bio-control agent for management of economically important arthropod pests (Burand, 1998; Huger, 1966). Historically, although a number of invertebrate viruses were claimed to be nudiviruses or nudivirus-like viruses (Burand, 1998; Huger and Krieg, 1991), only a few have somehow been studied in detail, such as the palm rhinoceros beetle (Oryctes rhinoceros) virus (Huger, 1966), the Hz-1 virus persistently replicating in the lepidopteran cell line IMC-Hz-1 (Granados et al.,
1978), the cricket (Gryllus bimaculatus) virus (Huger, 1985), and the most recently identified corn earworm moth (Heliothis zea) Hz-2 virus, formerly known as gonad-specific virus (GSV) (Herzog and Phillips, 1982; Raina and Adams, 1995). To accommodate these viruses, a new Nudivirus genus has been proposed. Consequently it has been suggested to rename these viruses OrNV, HzNV-1, GbNV, and HzNV-2, respectively, and we will use these terms in this review (Wang et al., 2007a,b,c). Currently, comparative genomic characterisation of nudiviruses shed new light into their phylogeny and classification as well as into the origin and evolution of baculoviruses and other invertebrate-specific large dsDNA viruses.
2. General features 2.1. Host stage and range
* Corresponding authors. Fax: +49 6321 671222. E-mail addresses: [email protected] (Y. Wang), [email protected] (J.A. Jehle). 0022-2011/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2009.03.013
With the exception of HzNV-1 that is unknown to replicate in vivo, nudiviruses infect both larvae and adults of their hosts
188
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193
via feeding and/or mating routes. Both OrNV and GbNV cause lethal infection in larvae but chronic disease in adults (Huger and Krieg, 1991). In contrast, upon HzNV-2 infection, host larvae appeared to be normal and adults were agonadal (Hamm et al., 1996; Raina and Adams, 1995; Raina et al., 2000). Neither of them died of the disease. Notably, based on genome and phylogenetic analyses, HzNV-1 and HzNV-2 were found to be very closely related isolates and shared all the four baculovirus per os infectivity core genes (pifs) (Wang et al., 2007c). However, HzNV-1 is incapable of infecting and replicating in host larvae by per os feeding and/or intra-hemocoelic injection (Granados et al., 1978), suggesting that other essential viral genes, but not the pifs, are blocked by the ‘‘resistant” host. Intensive comparative genomic and transcriptomic studies of these two viruses will be necessary (1) to discover the key functional genes associated with in vivo replication, (2) to uncover the molecular mechanisms of virus interaction with host, and (3) to cast light on how these viruses evolutionarily diverged under different environmental selection constraints. Nudiviruses have been observed world-wide in phylogenetically highly diverse arthropod hosts, suggesting their ancient origin and complex evolutionary history (Burand, 1998; Huger and Krieg, 1991). Most of the major insect orders, for example, from the very early divergent hemimetabolous Orthoptera to the most recent emerged holometabolous Lepidoptera are infected with one or more nudiviruses. Additionally, members of nudiviruses are supposed to be present in marine crustacean host such as shrimp and crab (Huger and Krieg, 1991). Based on sequence analyses and phylogenetic inference, we confirmed that the so-called occluded shrimp Monodon Baculovirus or Penaeus monodon nucleopolyhedrovirus belongs to the nudivirus group but not to baculoviruses (Table 1) (Wang and Jehle, unpublished). We propose to re-assign it to the genus Nudivirus and to rename it P. monodon nudivirus, PmNV. 2.2. Virus structure Nudiviruses are basically rod-shaped and measure 200 100 nm (Fig. 1) (Huger, 1966, 1985; Payne, 1974). In contrast, virions of HzNV-1, HzNV-2 and PmNV are longer and thinner (300– 400 80 nm) (Burand et al., 1983; Hamm et al., 1996; Lightner and Redman, 1981). Coincidently, this morphological grouping correlates with their phylogeny of two sister clades, consisting of OrNV/ GbNV and HzNVs/PmNV, respectively (see below). Except for HzNV1, the other four nudiviruses considered in this review all possess a protruding structure, which is located at the end of the OrNV nucleocapsid (Huger and Krieg, 1991), between envelope and nucleocapsid in both GbNV (Huger and Krieg, 1991) and HzNV-2 (Burand, 2008), or on the PmNV envelope surface (Johnson and Lightner, 1988; Mari et al., 1993). In addition, a tentative crab nudivirus also has a tail-like appendage alike that of OrNV (Huger and Krieg, 1991). Thus far, close to nothing is known about the biological functions and the relationship of these appendages. Interestingly, a similar appendage structure was also found on the envelope surface of shrimp white spot syndrome virus (WSSV), belonging to the genus Whispovirus within the family Nimaviridae (Vlak et al., 2005). WSSV resembles nudiviruses and baculoviruses in virion architecture, genome structure, and DNA replication strategy but shares few homologous genes with them (van Hulten et al., 2001; Yang et al., 2001). However, in the light of latest genomic analyses, an evolutionary link of WSSV to nudiviruses and baculoviruses appears to be supported (Wang and Jehle, unpublished). For a long time, nudiviruses have been thought to be non-occluded viruses (Burand, 1998; Huger and Krieg, 1991). However, this notion has to be revised and updated according to the most
recent findings. Based on gene sequence comparisons, there is strong evidence that PmNV, the so-called MBV, represents a new member of nudiviruses but it is occluded. Recently, its gene encoding occlusion bodies has been cloned and characterised, which bears no sequence similarities to any genes in the public databases and is not homologous to these two heterologous OB genes found in baculoviruses (Chaivisuthangkura et al., 2008). In addition, the facultative occurrence of OBs was observed in the two other nudiviruses OrNV and HzNV-2 (Huger and Krieg, 1991; Raina et al., 2000). Surprisingly, a homologue of lepidopteran- and hymenopteran-type polyhedrin/granulin gene was detected in all four completely sequenced nudivirus genomes (Wang and Jehle, unpublished). It remains unclear whether these genes functionally encode OB matrix proteins or what the biological function of the atypical nudivirus OBs is. It seems that the complex life-cycle of nudiviruses is far beyond exploration. However, it is obvious that OB formation should not be considered as a key criterion for distinguish nudiviruses from baculoviruses anymore. 2.3. Viral life cycle Life cycle of nudiviruses in either cell cultures or natural hosts is still poorly understood. Only fragmental data are available in the literature and are briefly reviewed here. OrNV becomes attached to and then internalized into cultured cells by pinocytosis, a form of endocytosis in which virus particles are brought into the cell by forming narrow channels through its membrane that pinch off into vesicles which subsequently fuse with lysosomes to hydrolyze or to break down, the particles (Crawford and Sheehan, 1985). But how the nucleocapsid is released from the viral envelope into the cytoplasm and how it is transported to the nucleus is unknown. It was suggested that the nucleocapsids uncoat at nuclear pore followed by release of the viral genome into the nucleoplasm (Quiot et al., 1973). Along with the cytopathic changes to the nuclear structure is the development of the virogenic stroma, where the envelopes and nucleocapsid shells are formed and then assembled with viral DNA (Burand, 2008). At a later stage, virions enter the cytoplasm followed by budding through the cell membrane (Crawford and Sheehan, 1985). In vitro sequential expression of viral genes encoding structural and intracellular proteins has been divided into early, intermediate and late stage in the replication cycle of OrNV and HzNV-1 (Burand, 1998; Crawford and Sheehan, 1985). 2.4. Transmission Given the facts that (1) not only a diverse group of host species colonising distinct ecological niches (2) but both larvae and adults become infected and that (3) nudivirus tissue tropism is variable among hosts, it is not surprising that nudiviruses have evolved complex and unusual transmission modes. OrNV and GbNV perorally invade hosts through fecal contaminated foods at nesting and mating sites (Huger, 1966, 1985). Uniquely, HzNV-2 is sexually transmitted between infected and susceptible moths during mating (Burand, 2008). It is vertically transmitted to host larvae through infected moths (Burand, 2008) and can also be acquired by larvae through feeding on diet mixed with virus (Raina and Lupiani, 2006). PmNV is horizontally transmitted by oral exposure to free viruses and OBs, contaminated tissues or fomites (Lightner et al., 1983). Besides, it is a general feature of nudiviruses to undergo latent and persistent infection of adult hosts. Nudivirus facultative OBs might also mediate the persistence of infectious viruses inside and/or outside hosts. The nudiviruses’ multiple transmission modes seem the key to successful infection of a taxonomically and ecologically wide variety of invertebrate hosts.
189
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193 Table 1 Homologous genes conserved in nudiviruses. Gene name
OrNV
GbNV
HzNV-1
PmNV
Function
dnapol helicase helicase 2 integrase ligase lef-3
1 34 108 75 121 59
12 88 46 57 38 86
131 104 60 144 36 –
N.d. N.d. N.d. + N.d. N.d.
DNA replication, repair, and recombination
rr1 rr2 tk tk tk tk
51 102 58 117 125 137
82 63 74 34 44 17
95 73 115 111 71 51
N.d. N.d. + + + +
Nucleotide metabolism
p47 lef-4 lef-8 lef-9 lef-5 vlf-1
20 42 64 96 52 30
69 96 49 24 85 80
75 98 90 75 101 121
N.d. N.d. N.d. + + +
Transcription
p74 pif-1 pif-2 pif-3
126 60 17 107
45 52 66 3
11 55 123 88
N.d. N.d. N.d. N.d.
Oral infectivity
16 33 72 87
65 87 55 1
69 103 74 10
N.d. N.d. N.d. +
Packaging, assembly, and morphogenesis
iap-3
134
98
138
N.d.
Inhibition of apoptosis
vp39 vp91 odv-e56 ac81 ac92
15 106 115 4 113 47 76 3 18 22 23 24 25 27 29 39 40 41 44 45 46 53 54 61 79 80 86 90 95 104 105 114 116 118 119 120 122 123 132 6 – – – – –
64 2 5 14 7 19 58 13 67 72 74 75 76 78 81 93 94 95 97 23 22 84 83 51 59 60 61 28 9 62 43 6 33 35 36 37 39 41 48 – – – – – –
89 46 76 33 13 30 143 – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 109 52 64 93 118 141
N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. + + + + +
Unknown function
polh/gran 19 kda ac68 38 K
–: Absent; +: Present; N.d.: Not determined. The predicted ORFs in nudiviruses are presented in number. Homologues to baculovirus core genes are marked in bold face.
190
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193
Fig. 1. Electron micrographs of GbNV particles. (a) Thin section of infected cell nucleus. (b) Purified virions. Inset: enlarged image of a typical virion showing the envelope and the rod-shaped nucleocapsid. Bar: 200 nm in a and b and 20 nm in inset. (courtesy of Dr. Alois M. Huger, JKI Darmstadt).
3. Genomics 3.1. General features HzNV-1 was the first completely sequenced nudivirus (Cheng et al., 2002). Its genome is 228,089 bp in size encoding 154 ORFs and has a G+C content of 42%. These ORFs are randomly distributed on both DNA strands with 45% clockwise orientation and 55% counterclockwise orientation. Later on, the genome of OrNV, the first discovered nudivirus, was partially sequenced (Wang et al., 2007a). The genome of the GbNV is 96,944 bp in length, has a G+C content of 28%, and contains 98 ORFs (Wang et al., 2007b). 58% of its ORFs are in clockwise distribution; 42% are in reverse direction (Wang et al., 2007b). HzNV-2, the close relative to HzNV-1, has also been sequenced and has a genome of 231,621 bp, only slightly longer than that of HzNV-1, with a G+C content of 42% identical to HzNV-1 (Wang et al., 2007c). HzNV-1 and HzNV-2 share 99% nucleotide sequence identity and encode similar numbers of ORFs (Burand, 2008). Recently, sequencing the complete genome of OrNV was successfully achieved by using DNA generated by multiple displacement amplification (MDA) (Wang et al., 2008). The OrNV genome is 127,615 bp in size and contains 139 ORFs and a G+C content of 42% (Wang et al., 2008); Wang and Jehle, unpublished). Sequencing of other nudivirus genomes such as the shrimp PmNV is ongoing; partial nucleotide sequences are already accessible in GenBank. Repetitive sequences (RS) were detected in all sequenced nudivirus genomes. They are variable in length and numbers and are distributed throughout the genome. They are homologous neither to each other within and between genomes, nor to those of other large dsDNA viruses, such as baculoviruses, SGHVs and WSSV. RS appear to be a universal feature of all large dsDNA viruses. 3.2. Gene content and function As shown in Table 1, there are 66, 34, and 33 homologous genes shared by OrNV and GbNV, OrNV and HzNV-1, and GbNV and HzNV-1, respectively, suggesting that OrNV and GbNV are more closely related to each other than to HzNV-1. All sequenced nudivirus genomes have 33 genes in common. Strikingly, 20 out of them are homologues of baculovirus core genes, which are present in all 48 baculovirus genomes that have been deposited in GenBank as of February 2009. All baculoviruses share 30 core genes, which play crucial role in baculovirus replication cycle and are the evolutionary marker genes for baculovirus identification, classification and phylogeny (Herniou et al., 2003; Herniou and Jehle,
2007; Jehle et al., 2006a; Jehle et al., 2006b; van Oers and Vlak, 2007). Surprisingly, one conserved nudivirus ORF is similar to the baculovirus polh/gran gene encoding the OB protein in Alpha-, Beta- and Gammabaculoviruses. Nine other ORFs are likely involved in DNA replication, DNA repair and recombination, and nucleotide metabolism; one is homologous to baculovirus iap-3 gene; two others are nudivirus-specific ORFs of unknown function. The conservation of 20 baculovirus core genes in nudiviruses strongly indicates that nudiviruses and baculoviruses are much more closely related to each other than to any other viruses known so far. Besides in nudiviruses, interestingly, homologues to baculovirus core genes were detected recently in two unassigned salivary gland hypertrophy viruses (SGHVs), infecting the house fly Musca domestica (MdSGHV) and the tsetse fly Glossina pallidipes (GpSGHV), respectively (Abd-Alla et al., 2008; Garcia-Maruniak et al., 2008). The 190 kbp genome of GpSGHV is composed of 160 ORFs and has a low G+C content of 28% (Abd-Alla et al., 2008), whereas the 124 kbp genome of MdSGHV contains 108 ORFs with a G+C content of 44% (Garcia-Maruniak et al., 2008). 37 MdSGHV ORFs are homologous to 42 GpSGHV ORFs (Garcia-Maruniak et al., 2009); GpSGHV and MdSGHV are phylogenetically closely related (Garcia-Maruniak et al., 2009). Accordingly, the new viral family ‘‘Hytrosaviridae” was proposed to classify SGHVs (Abd-Alla et al., 2009). In addition, several homologous baculovirus core genes could be also identified in the marine WSSV (Wang and Jehle, unpublished), suggesting that WSSV is evolutionarily related, albeit distantly, to baculoviruses, nudiviruses, and SGHVs. This finding provides crucial clues to dating back to the origin of arthropodspecific large DNA viruses. Most strikingly, nudiviruses, SGHVs and WSSV have the homologues to these four genes encoding peroral infectivity factors (p74, pif-1, pif-2 and pif-3) (Wang and Jehle, unpublished), which are conserved among all baculoviruses and are absolutely essential for successful peroral infection of insects. As midgut infection is the crucial first step in the pathogenesis of baculoviruses, PIFs may be important determinants of host range and virulence. Consequently, hypothesising a highly conserved interaction mode upon primary infection in baculoviruses, nudivirusees, SGHVs and WSSV seems to be plausible. However, only scattered information on the function of the PIF proteins has been delineated (Slack and Arif, 2007). Further deciphering of the molecular mechanisms of their key role in oral infection of invertebrate hosts will be crucial to understand host range, zoonotic behaviour, and epizootic or enzootic disease of these viruses. Additionally, nudiviruses and SGHVs also appear to share homologues of the
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193
191
RNA transcription apparatus of baculoviruses suggesting that these viruses use a similar mode of late gene transcription (Wang and Jehle, unpublished). The in vivo biochemical and biological function of the genes predicted in nudiviruses remains unknown. Only the occlusion body-encoding gene in PmNV has been molecularly identified (Chaivisuthangkura et al., 2008). 3.3. Gene order Gene order is poorly conserved in nudivirus genomes. OrNV and GbNV share a number of gene clusters comprising 2–7 collinearly arranged genes, distributed throughout their genomes (Fig. 2). In contrast, only two gene clusters were detected between OrNV and HzNV-1. However, a gene cluster of helicase, 19 kda, and/or lef-5 is present in all nudivirus genomes, which is similar to the conserved core gene cluster of four genes of helicase, 19 kda, 38 K and lef-5 is found in all baculoviruses (Herniou et al., 2003; Jehle and Backhaus, 1994). Hence, both core gene content and gene clustering strongly support the hypothesis of a common ancestor of nudiviruses and baculoviruses. 4. Phylogeny and evolution Members of nudiviruses possess interesting biological and molecular properties and show broad ‘‘ecological” and phylogenetic host range, making them ideal to study virus evolution. But it is only since their genomes have been recently sequenced and characterised that deeper insights into nudivirus evolutionary history became accessible. In the phylogenetic tree of large circular dsDNA viruses, nudiviruses are monophyletic (Fig. 3). HzNVs are close relatives and share a recent common ancestor with PmNV (Fig. 3) (Wang et al., 2007c); OrNV and GbNV were clustered in a single group and diverged from the common ancestor of PmNV and HzNVs. It is proposed that nudiviruses and baculoviruses are sister lineages, which diverged early from SGHVs and WSSV (Wang and Jehle, unpublished). The tree branching pattern is in agreement with gene content analyses revealing a decreasing number of gene homologues shared between nudiviruses, baculoviruses, SGHVs and WSSV. It also correctly reproduces our present-day picture of baculovirus phylogeny, with dipteran and hymenopteran NPVs as basal branches and two sister-groups of lepidopteran NPVs and GVs (Jehle et al., 2006a). The common ancestor of nudiviruses and baculoviruses did not date back to the ancient origin of arthropods and their evolution was likely shaped by the interaction between the viruses and their hosts and was driven by the specific ecological niches the hosts colonise. It is conceivable that these large dsDNA viruses derived from a marine ancestor virus.
Fig. 2. Gene parity plots of OrNV versus GbNV and HzNV-1 genomes, respectively. Each ORF is shown in a black square following the order from 1 to 139 on the x-axis (left to right) and from 1 to 98 for GbNV and 1 to 154 for HzNV-1 on the y-axis (up to down). ORFs with similarity fall inside the two axes, while ORFs without similarity appear on the outside of the axis. The gene cluster of helicase and 19 kda conserved in both nudiviruses and baculoviruses is marked in a dashed circle.
Fig. 3. Nudivirus phylogeny. The tree is adapted from (Wang and Jehle, unpublished) and was constructed by using the supermatrix method (de Queiroz and Gatesy, 2007), simultaneously analysing a set of conserved homologous genes present in nudiviruses, baculoviruses, SGHVs, and WSSV (Wang and Jehle, unpublished).
5. Classification Recently, the viral genus Nudivirus together with demarcation criteria and naming strategies has been proposed for classification of nudiviruses, which appears to be still reliable (Wang et al., 2007a,b,c). What needs to be reconsidered here is the criterion of OB formation. OB formation is a widespread phenomenon in several insect-infecting viral taxa, such as the Baculoviridae, the Entomopoxvirinae and the Cypovirus (Reoviridae) (Buller et al., 2005; Mertens et al., 2005). It seems to be a highly successful convergent adaptation of many insect viruses to persist outside the host. As mentioned above, clearly, some members of nudiviruses, if not all, do generate OBs. OB formation likely plays a less distinct ecological role in the life-cycle of nudiviruses than in that of baculoviruses. However, deeming nudiviruses as non-occluded viruses is not justified. Taking into account the important role of non-occluded virions in nudivirus enzootics, there is no linguistic disaccord in retaining the name nudivirus for these viruses. Another concern is their appropriate classification into a virus subfamily or family. Presently, nudiviruses comprise five tentative species, OrNV, GbNV, HzNV-1, HzNV-2, and PmNV. According to their similarities to baculoviruses, the formation of a subfamily ‘‘Nudivirinae” within the family Baculoviridae might be feasible. On the other hand, however, given their distinct biological and ecological features as well as their virion properties, the establishment of an independent family ‘‘Nudiviridae” within a new order ‘‘Baculovirales” along with the Baculoviridae seems also conceivable. The latter might be most pragmatic since the establishment of such an order may allow subsequent flexible integration of other ‘‘baculovirus-related” but highly diverged viruses, such as the proposed ‘‘Hytrosaviridae” or the Nimaviridae, without taxonomic re-definition of the family Baculoviridae. 6. Conclusions and perspectives The recent advances in nudivirus genome analyses clearly cast new lights on their biological properties as well as their phyloge-
192
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193
netic origin and evolution. Phylogenetically, nudiviruses represent a distinct lineage of large DNA viruses and are related to baculoviruses. Importantly, their evolutionary relationship to other large DNA viruses such as SGHVs and WSSV has been evidenced, paving the way for further exploring the divergent evolution of invertebrate-specific large dsDNA viruses. Recently, the groundbreaking findings by Bézier et al. (2009a,b) showing that bracoviruses, the symbiotic large DNA viruses of Hymenoptera, derived from an ancestral nudivirus, challenge our current understanding of how nudiviruses originated and evolved (see also in Bézier et al., 2009b). However, studying nudiviruses is still in its infancy. Among the more than 400 annotated nudivirus ORFs, only very few have been biochemically characterised. Little is known about their role in the virus infection and replication process. Hence, the functional characterisation of these genes, in particular of the conserved core genes, is urgent and will bring about a glimmer of light into the shadowy scientific existence of nudiviruses. Acknowledgments This paper was the result of a presentation on Comparative Genomics of DNA viruses at the 41st Annual Meeting of the Society for Invertebrate Pathology (University of Warwick, UK, August 3–7, 2008), for which we thank Elisabeth A. Herniou for the invitation to attend. We are indebted to Regina G. Kleespies and Alois M. Huger for providing the GbNV photos. We thank Monique M. van Oers, Just M. Vlak, Regina G. Kleespies, Alois M. Huger, Moslim B. Ramle, and Trevor Jackson for fruitful cooperation, and Adly M. M. AbdAlla, Alejandra Garcia-Maruniak, John P. Burand, and Jean-Michel Drezen for communications and discussions. Financial supports were provided through the research projects by the Deutsche Forschungsgemeinschaft (DFG Je245-7). References Abd-Alla, A.M.M., Cousserans, F., Parker, A.G., Jehle, J.A., Parker, N.J., Vlak, J.M., Robinson, A.S., Bergoin, M., 2008. Genome analysis of a Glossina pallidipes salivary gland hypertrophy virus reveals a novel, large, double-stranded circular DNA virus. J. Virol. 82, 4595–4611. Abd-Alla, A.M.M., Vlak, J.M., Bergoin, M., Maruniak, J.E., Parker, A., Burand, J.P., Jehle, J.A., Boucias, D.G., 2009. Hytrosaviridae: a proposal for classification and nomenclature of a new insect virus family. Arch. Virol. 154, 909–918. Bézier, A., Annaheim, M., Herbinière, J., Wetterwald, C., Gyapay, G., Bernard-Samain, S., Wincker, P., Roditi, I., Heller, M., Belghazi, M., Pfister-Wilhem, R., Periquet, G., Dupuy, C., Huguet, E., Volkoff, A.N., Lanzrein, B., Drezen, J.M., 2009a. Polydnaviruses of braconid wasps derive from an ancestral nudivirus. Science 323, 926–930. Bézier, A., Herbinière, J., Lanzrein, B., Drezen, J.M., 2009b. Polydnavirus hidden face: The genes producing virus particles of parasitic wasps. J. Invertebr. Pathol. 101, 194–203. Buller, R.M., Arif, B.M., Black, D.N., Dumbell, K.R., Esposito, J.J., Lefkowitz, E.J., McFadden, G., Moss, B., Mercer, A.A., Moyer, R.W., Skinner, M.A., Tripathy, D.N., 2005. Poxviridae. In: Fauquet, C.M., Mayo, M.A., Maniloff, J., Desselberger, U., Ball, L.A. (Eds.), Virus Taxonomy. Classification and Nomenclature of Viruses. Eighth Report of the International Committee on Taxonomy of Viruses. Elsevier, Academic Press, New York, pp. 117–133. Burand, J.P., 1998. Nudiviruses. In: Miller, L.K., Ball, L.A. (Eds.), The Insect Viruses. Plenum Press, New York, pp. 69–90. Burand, J.P., 2008. Insect viruses: nonoccluded. In: Mahy, B.W.J., Van Regenmortel, M.H.V. (Eds.), Encyclopedia of Virology. Elsevier, Oxford, pp. 144–148. Burand, J.P., Stiles, B., Wood, H.A., 1983. Structural and intracellular proteins of the nonoccluded baculovirus Hz-1. J. Virol. 46, 137–142. Chaivisuthangkura, P., Tawilert, C., Tejangkura, T., Rukpratanporn, S., Longyant, S., Sithigorngul, W., Sithigorngul, P., 2008. Molecular isolation and characterization of a novel occlusion body protein gene from Penaeus monodon nucleopolyhedrovirus. Virology 381, 261–267. Cheng, C.H., Liu, S.M., Chow, T.Y., Hsiao, Y.Y., Wang, D.P., Huang, J.J., Chen, H.H., 2002. Analysis of the complete genome sequence of the Hz-1 virus suggests that it is related to members of the Baculoviridae. J. Virol. 76, 9024–9034. Crawford, A.M., Sheehan, C., 1985. Replication of Oryctes baculovirus in cell culture: viral morphogenesis, infectivity and protein synthesis. J. Gen. Virol. 66, 529– 539. de Queiroz, A., Gatesy, J., 2007. The supermatrix approach to systematics. Trends Ecol. Evol. 22, 34–41.
Garcia-Maruniak, A., Maruniak, J.E., Farmerie, W., Boucias, D.G., 2008. Sequence analysis of a non-classified, non-occluded DNA virus that causes salivary gland hypertrophy of Musca domestica, MdSGHV. Virology 377, 184–196. Garcia-Maruniak, A., Abd-Alla, A.M.M., Salem, T.Z., Parker, A.G., Lietze, V.-U., van Oers, M.M., Maruniak, J.E., Kim, W., Burand, J.P., Cousserans, F., Robinson, A.S., Vlak, J.M., Bergoin, M., Boucias, D.G., 2009. Two viruses that cause salivary gland hypertrophy in Glossina pallidipes and Musca domestica are related and form a distinct phylogenetic clade. J. Gen. Virol. 90, 334–346. Granados, R.R., Nguyen, T., Cato, B., 1978. An insect cell line persistently infected with a baculovirus-like particle. Intervirology 10, 309–317. Hamm, J.J., Carpenter, J.E., Styer, E.L., 1996. Oviposition day effect on incidence of agonadal progeny of Helicoverpa zea (Lepidoptera: Noctuidae) infected with a virus. Ann. Entomol. Soc. Am. 56, 535–556. Herniou, E.A., Jehle, J.A., 2007. Baculovirus phylogeny and evolution. Curr. Drug Targets 8, 1043–1050. Herniou, E.A., Olszewski, J.A., Cory, J.S., O’Reilly, D.R., 2003. The genome sequence and evolution of baculoviruses. Annu. Rev. Entomol. 48, 211–234. Herzog, G.A., Phillips, J.R., 1982. Manifestation of an abnormal reproductive system in a laboratory strain of the bollworm Heliothis zea. J. Ga. Entomol. Soc. 17, 506. Huger, A.M., 1966. A virus disease of the Indian rhinoceros beetle, Oryctes rhinoceros (Linnaeus), caused by a new type of insect virus, Rhabdionvirus oryctes gen. n., sp. n. J. Invertebr. Pathol. 8, 38–51. Huger, A.M., 1985. A new virus disease of crickets (Orthoptera: Gryllidae) causing macronucleosis of fatbody. J. Invertebr. Pathol. 45, 108–111. Huger, A.M., Krieg, A., 1991. Baculoviridae. Nonoccluded baculoviruses. In: Adams, J.R., Bonami, J.R. (Eds.), Atlas of Invertebrate Viruses. CRC Press, Inc., Boca Raton, pp. 287–319. Jehle, J.A., Backhaus, H., 1994. Genome organization of the DNA-binding protein gene region of Cryptophlebia leucotreta granulosis virus is closely related to that of nuclear polyhedrosis viruses. J. Gen. Virol. 75, 1815–1820. Jehle, J.A., Blissard, G.W., Bonning, B.C., Cory, J.S., Herniou, E.A., Rohrmann, G.F., Theilmann, D.A., Thiem, S.M., Vlak, J.M., 2006a. On the classification and nomenclature of baculoviruses: a proposal for revision. Arch. Virol. 151, 1257– 1266. Jehle, J.A., Lange, M., Wang, H., Hu, Z., Wang, Y., Hauschild, R., 2006b. Molecular identification and phylogenetic analysis of baculoviruses from Lepidoptera. Virology 346, 180–193. Johnson, P.T., Lightner, D.V., 1988. Rod-shaped nuclear viruses of crustaceans: gutinfecting species. Dis. Aquat. Org. 5, 123–141. Lightner, D.V., Redman, R.M., 1981. A baculovirus-caused disease of the penaeid shrimp, Penaeus monodon. J. Invertebr. Pathol. 38, 299–302. Lightner, D.V., Redman, R.M., Bell, T.A., 1983. Observations on the geographic distribution, pathogenesis and morphology of the baculovirus from Penaeus monodon Fabricius. Aquaculture 32, 209–233. Mari, J., Bonami, J.-R., Poulos, B., Lightner, D., 1993. Preliminary characterization and partial cloning of the genome of a baculovirus from Penaeus monodon (PmSNPV = MBV). Dis. Aquat. Org. 16, 207–215. Mertens, P.P.C., Rao, S., Zhou, Z.H., 2005. Reoviridae – Cypovirus. In: Fauquet, C.M., Mayo, M.A., Maniloff, J., Desselberger, U., Ball, L.A. (Eds.), Virus Taxonomy. Classification and Nomenclature of Viruses. Eighth Report of the International Committee on Taxonomy of Viruses. Elsevier Academic Press, New York, pp. 522–533. Payne, C.C., 1974. The isolation and characterization of a virus from Oryctes rhinoceros. J. Gen. Virol. 25, 105–116. Quiot, J.-M., Monsarrat, P., Meynadler, G., Croizier, G., Vago, C., 1973. Infection des cultures cellulaires de Coléoptères par le ‘virus Oryctes’. CR. Acad. Sci. Ser. D 276, 3229–3231. Raina, A.K., Adams, J.R., 1995. Gonad-specific virus of corn earworm. Nature 374, 770. Raina, A.K., Lupiani, B., 2006. Acquisition, persistence, and species susceptibility of the Hz-2V virus. J. Invertebr. Pathol. 93, 71–74. Raina, A.K., Adams, J.R., Lupiani, B., Lynn, D.E., Kim, W., Burand, J.P., Dougherty, E.M., 2000. Further characterization of the gonad-specific virus of corn earworm, Helicoverpa zea. J. Invertebr. Pathol. 76, 6–12. Rohrmann, G.F., 2008. Baculovirus Molecular Biology. National Library of Medicine (US), NCBI, Bethesda (MD). Slack, J., Arif, B.M., 2007. The baculoviruses occlusion-derived virus: virion structure and function. Adv. Virus Res. 69, 99–165. van Hulten, M.C., Witteveldt, J., Peters, S., Kloosterboer, N., Tarchini, R., Fiers, M., Sandbrink, H., Lankhorst, R.K., Vlak, J.M., 2001. The white spot syndrome virus DNA genome sequence. Virology 286, 7–22. van Oers, M.M., Vlak, J.M., 2007. Baculovirus genomics. Curr. Drug Targets 8, 1051– 1068. Vlak, J.M., Bonami, J.R., Flegel, T.W., Kou, G.H., Lightner, D.V., Lo, C.F., Loh, P.C., Walker, P.W., 2005. Nimaviridae. In: Fauquet, C.M., Mayo, M.A., Maniloff, J., Desselberger, U., Ball, L.A. (Eds.), Virus Taxonomy. Classification and Nomenclature of Viruses. Eighth Report of the International Committee on Taxonomy of Viruses. Elsevier, Academic Press, New York, pp. 187–192. Wang, Y., van Oers, M.M., Crawford, A.M., Vlak, J.M., Jehle, J.A., 2007a. Genomic analysis of Oryctes rhinoceros virus reveals genetic relatedness to Heliothis zea virus 1. Arch. Virol. 152, 519–531. Wang, Y., Kleespies, R.G., Huger, A.M., Jehle, J.A., 2007b. The genome of Gryllus bimaculatus nudivirus indicates an ancient diversification of baculovirus-related nonoccluded nudiviruses of insects. J. Virol. 81, 5395–5406. Wang, Y., Burand, J.P., Jehle, J.A., 2007c. Nudivirus genomics: diversity and classification. Virologica Sinica 22, 128–136.
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193 Wang, Y., Kleespies, R.G., Ramle, M.B., Jehle, J.A., 2008. Sequencing of the large dsDNA genome of Oryctes rhinoceros nudivirus using multiple displacement amplification of nanogram amounts of virus DNA. J. Virol. Methods 152, 106–108.
193
Yang, F., He, J., Lin, X., Li, Q., Pan, D., Zhang, X., Xu, X., 2001. Complete genome sequence of the shrimp white spot bacilliform virus. J. Virol. 75, 11811– 11820.
Contents lists available at ScienceDirect
Journal of Invertebrate Pathology journal homepage: www.elsevier.com/locate/yjipa
Nudiviruses and other large, double-stranded circular DNA viruses of invertebrates: New insights on an old topic Yongjie Wang *, Johannes A. Jehle * Laboratory for Biotechnological Crop Protection, Department of Phytopathology, Agricultural Service Center Palatinate (DLR Rheinpfalz), Breitenweg 71, 67435, Neustadt a.d. Weinstrasse, Germany
a r t i c l e
i n f o
Article history: Received 6 March 2009 Accepted 9 March 2009 Available online 19 May 2009 Keywords: Nudiviruses Baculoviruses Monodon Baculovirus Salivary gland hypertrophy virus White spot syndrome virus Large DNA viruses Genome Evolution Phylogeny Classification
a b s t r a c t Nudiviruses (NVs) are a highly diverse group of large, circular dsDNA viruses pathogenic for invertebrates. They have rod-shaped and enveloped nucleocapsids, replicate in the nucleus of infected host cells, and possess interesting biological and molecular properties. The unassigned viral genus Nudivirus has been proposed for classification of nudiviruses. Currently, the nudiviruses comprise five different viruses: the palm rhinoceros beetle virus (Oryctes rhinoceros NV, OrNV), the Hz-1 virus (Heliothis zea NV-1, HzNV1), the cricket virus (Gryllus bimaculatus NV, GbNV), the corn earworm moth Hz-2 virus (HzNV-2), and the occluded shrimp Monodon Baculovirus reassigned as Penaeus monodon NV (PmNV). Thus far, the genomes of OrNV, GbNV, HzNV-1 and HzNV-2 have been completely sequenced. They vary between 97 and 230 kbp in size and encode between 98 and 160 open reading frames (ORFs). All sequenced nudiviruses have 33 ORFs in common. Strikingly, 20 of them are homologous to baculovirus core genes involved in RNA transcription, DNA replication, virion structural components and other functions. Another nine conserved ORFs are likely associated with DNA replication, repair and recombination, and nucleotide metabolism; one is homologous to baculovirus iap-3 gene; two are nudivirus-specific ORFs of unknown function. Interestingly, one nudivirus ORF is similar to polh/gran gene, encoding occlusion body protein matrix and being conserved in Alpha- Beta- and Gammabaculoviruses. Members of nudiviruses are closely related and form a monophyletic group consisting of two sister clades of OrNV/ GbNV and HzNVs/PmNV. It is proposed that nudiviruses and baculoviruses derived from a common ancestor and are evolutionarily related to other large DNA viruses such as the insect-specific salivary gland hypertrophy virus (SGHV) and the marine white spot syndrome virus (WSSV). Ó 2009 Elsevier Inc. All rights reserved.
1. Introduction Nudiviruses (Latin nudi = bare, naked, uncovered) comprise a diverse group of large double-stranded (ds) DNA viruses pathogenic for aquatic and terrestrial invertebrates. Like insect-specific baculoviruses (Rohrmann, 2008), they have rod-shaped and enveloped nucleocapsids and replicate in the nucleus of infected host cells resulting in nuclear hypertrophy (Burand, 1998). Nudiviruses (NVs) are considered to be potential bio-control agent for management of economically important arthropod pests (Burand, 1998; Huger, 1966). Historically, although a number of invertebrate viruses were claimed to be nudiviruses or nudivirus-like viruses (Burand, 1998; Huger and Krieg, 1991), only a few have somehow been studied in detail, such as the palm rhinoceros beetle (Oryctes rhinoceros) virus (Huger, 1966), the Hz-1 virus persistently replicating in the lepidopteran cell line IMC-Hz-1 (Granados et al.,
1978), the cricket (Gryllus bimaculatus) virus (Huger, 1985), and the most recently identified corn earworm moth (Heliothis zea) Hz-2 virus, formerly known as gonad-specific virus (GSV) (Herzog and Phillips, 1982; Raina and Adams, 1995). To accommodate these viruses, a new Nudivirus genus has been proposed. Consequently it has been suggested to rename these viruses OrNV, HzNV-1, GbNV, and HzNV-2, respectively, and we will use these terms in this review (Wang et al., 2007a,b,c). Currently, comparative genomic characterisation of nudiviruses shed new light into their phylogeny and classification as well as into the origin and evolution of baculoviruses and other invertebrate-specific large dsDNA viruses.
2. General features 2.1. Host stage and range
* Corresponding authors. Fax: +49 6321 671222. E-mail addresses: [email protected] (Y. Wang), [email protected] (J.A. Jehle). 0022-2011/$ - see front matter Ó 2009 Elsevier Inc. All rights reserved. doi:10.1016/j.jip.2009.03.013
With the exception of HzNV-1 that is unknown to replicate in vivo, nudiviruses infect both larvae and adults of their hosts
188
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193
via feeding and/or mating routes. Both OrNV and GbNV cause lethal infection in larvae but chronic disease in adults (Huger and Krieg, 1991). In contrast, upon HzNV-2 infection, host larvae appeared to be normal and adults were agonadal (Hamm et al., 1996; Raina and Adams, 1995; Raina et al., 2000). Neither of them died of the disease. Notably, based on genome and phylogenetic analyses, HzNV-1 and HzNV-2 were found to be very closely related isolates and shared all the four baculovirus per os infectivity core genes (pifs) (Wang et al., 2007c). However, HzNV-1 is incapable of infecting and replicating in host larvae by per os feeding and/or intra-hemocoelic injection (Granados et al., 1978), suggesting that other essential viral genes, but not the pifs, are blocked by the ‘‘resistant” host. Intensive comparative genomic and transcriptomic studies of these two viruses will be necessary (1) to discover the key functional genes associated with in vivo replication, (2) to uncover the molecular mechanisms of virus interaction with host, and (3) to cast light on how these viruses evolutionarily diverged under different environmental selection constraints. Nudiviruses have been observed world-wide in phylogenetically highly diverse arthropod hosts, suggesting their ancient origin and complex evolutionary history (Burand, 1998; Huger and Krieg, 1991). Most of the major insect orders, for example, from the very early divergent hemimetabolous Orthoptera to the most recent emerged holometabolous Lepidoptera are infected with one or more nudiviruses. Additionally, members of nudiviruses are supposed to be present in marine crustacean host such as shrimp and crab (Huger and Krieg, 1991). Based on sequence analyses and phylogenetic inference, we confirmed that the so-called occluded shrimp Monodon Baculovirus or Penaeus monodon nucleopolyhedrovirus belongs to the nudivirus group but not to baculoviruses (Table 1) (Wang and Jehle, unpublished). We propose to re-assign it to the genus Nudivirus and to rename it P. monodon nudivirus, PmNV. 2.2. Virus structure Nudiviruses are basically rod-shaped and measure 200 100 nm (Fig. 1) (Huger, 1966, 1985; Payne, 1974). In contrast, virions of HzNV-1, HzNV-2 and PmNV are longer and thinner (300– 400 80 nm) (Burand et al., 1983; Hamm et al., 1996; Lightner and Redman, 1981). Coincidently, this morphological grouping correlates with their phylogeny of two sister clades, consisting of OrNV/ GbNV and HzNVs/PmNV, respectively (see below). Except for HzNV1, the other four nudiviruses considered in this review all possess a protruding structure, which is located at the end of the OrNV nucleocapsid (Huger and Krieg, 1991), between envelope and nucleocapsid in both GbNV (Huger and Krieg, 1991) and HzNV-2 (Burand, 2008), or on the PmNV envelope surface (Johnson and Lightner, 1988; Mari et al., 1993). In addition, a tentative crab nudivirus also has a tail-like appendage alike that of OrNV (Huger and Krieg, 1991). Thus far, close to nothing is known about the biological functions and the relationship of these appendages. Interestingly, a similar appendage structure was also found on the envelope surface of shrimp white spot syndrome virus (WSSV), belonging to the genus Whispovirus within the family Nimaviridae (Vlak et al., 2005). WSSV resembles nudiviruses and baculoviruses in virion architecture, genome structure, and DNA replication strategy but shares few homologous genes with them (van Hulten et al., 2001; Yang et al., 2001). However, in the light of latest genomic analyses, an evolutionary link of WSSV to nudiviruses and baculoviruses appears to be supported (Wang and Jehle, unpublished). For a long time, nudiviruses have been thought to be non-occluded viruses (Burand, 1998; Huger and Krieg, 1991). However, this notion has to be revised and updated according to the most
recent findings. Based on gene sequence comparisons, there is strong evidence that PmNV, the so-called MBV, represents a new member of nudiviruses but it is occluded. Recently, its gene encoding occlusion bodies has been cloned and characterised, which bears no sequence similarities to any genes in the public databases and is not homologous to these two heterologous OB genes found in baculoviruses (Chaivisuthangkura et al., 2008). In addition, the facultative occurrence of OBs was observed in the two other nudiviruses OrNV and HzNV-2 (Huger and Krieg, 1991; Raina et al., 2000). Surprisingly, a homologue of lepidopteran- and hymenopteran-type polyhedrin/granulin gene was detected in all four completely sequenced nudivirus genomes (Wang and Jehle, unpublished). It remains unclear whether these genes functionally encode OB matrix proteins or what the biological function of the atypical nudivirus OBs is. It seems that the complex life-cycle of nudiviruses is far beyond exploration. However, it is obvious that OB formation should not be considered as a key criterion for distinguish nudiviruses from baculoviruses anymore. 2.3. Viral life cycle Life cycle of nudiviruses in either cell cultures or natural hosts is still poorly understood. Only fragmental data are available in the literature and are briefly reviewed here. OrNV becomes attached to and then internalized into cultured cells by pinocytosis, a form of endocytosis in which virus particles are brought into the cell by forming narrow channels through its membrane that pinch off into vesicles which subsequently fuse with lysosomes to hydrolyze or to break down, the particles (Crawford and Sheehan, 1985). But how the nucleocapsid is released from the viral envelope into the cytoplasm and how it is transported to the nucleus is unknown. It was suggested that the nucleocapsids uncoat at nuclear pore followed by release of the viral genome into the nucleoplasm (Quiot et al., 1973). Along with the cytopathic changes to the nuclear structure is the development of the virogenic stroma, where the envelopes and nucleocapsid shells are formed and then assembled with viral DNA (Burand, 2008). At a later stage, virions enter the cytoplasm followed by budding through the cell membrane (Crawford and Sheehan, 1985). In vitro sequential expression of viral genes encoding structural and intracellular proteins has been divided into early, intermediate and late stage in the replication cycle of OrNV and HzNV-1 (Burand, 1998; Crawford and Sheehan, 1985). 2.4. Transmission Given the facts that (1) not only a diverse group of host species colonising distinct ecological niches (2) but both larvae and adults become infected and that (3) nudivirus tissue tropism is variable among hosts, it is not surprising that nudiviruses have evolved complex and unusual transmission modes. OrNV and GbNV perorally invade hosts through fecal contaminated foods at nesting and mating sites (Huger, 1966, 1985). Uniquely, HzNV-2 is sexually transmitted between infected and susceptible moths during mating (Burand, 2008). It is vertically transmitted to host larvae through infected moths (Burand, 2008) and can also be acquired by larvae through feeding on diet mixed with virus (Raina and Lupiani, 2006). PmNV is horizontally transmitted by oral exposure to free viruses and OBs, contaminated tissues or fomites (Lightner et al., 1983). Besides, it is a general feature of nudiviruses to undergo latent and persistent infection of adult hosts. Nudivirus facultative OBs might also mediate the persistence of infectious viruses inside and/or outside hosts. The nudiviruses’ multiple transmission modes seem the key to successful infection of a taxonomically and ecologically wide variety of invertebrate hosts.
189
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193 Table 1 Homologous genes conserved in nudiviruses. Gene name
OrNV
GbNV
HzNV-1
PmNV
Function
dnapol helicase helicase 2 integrase ligase lef-3
1 34 108 75 121 59
12 88 46 57 38 86
131 104 60 144 36 –
N.d. N.d. N.d. + N.d. N.d.
DNA replication, repair, and recombination
rr1 rr2 tk tk tk tk
51 102 58 117 125 137
82 63 74 34 44 17
95 73 115 111 71 51
N.d. N.d. + + + +
Nucleotide metabolism
p47 lef-4 lef-8 lef-9 lef-5 vlf-1
20 42 64 96 52 30
69 96 49 24 85 80
75 98 90 75 101 121
N.d. N.d. N.d. + + +
Transcription
p74 pif-1 pif-2 pif-3
126 60 17 107
45 52 66 3
11 55 123 88
N.d. N.d. N.d. N.d.
Oral infectivity
16 33 72 87
65 87 55 1
69 103 74 10
N.d. N.d. N.d. +
Packaging, assembly, and morphogenesis
iap-3
134
98
138
N.d.
Inhibition of apoptosis
vp39 vp91 odv-e56 ac81 ac92
15 106 115 4 113 47 76 3 18 22 23 24 25 27 29 39 40 41 44 45 46 53 54 61 79 80 86 90 95 104 105 114 116 118 119 120 122 123 132 6 – – – – –
64 2 5 14 7 19 58 13 67 72 74 75 76 78 81 93 94 95 97 23 22 84 83 51 59 60 61 28 9 62 43 6 33 35 36 37 39 41 48 – – – – – –
89 46 76 33 13 30 143 – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – – 109 52 64 93 118 141
N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. N.d. + + + + +
Unknown function
polh/gran 19 kda ac68 38 K
–: Absent; +: Present; N.d.: Not determined. The predicted ORFs in nudiviruses are presented in number. Homologues to baculovirus core genes are marked in bold face.
190
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193
Fig. 1. Electron micrographs of GbNV particles. (a) Thin section of infected cell nucleus. (b) Purified virions. Inset: enlarged image of a typical virion showing the envelope and the rod-shaped nucleocapsid. Bar: 200 nm in a and b and 20 nm in inset. (courtesy of Dr. Alois M. Huger, JKI Darmstadt).
3. Genomics 3.1. General features HzNV-1 was the first completely sequenced nudivirus (Cheng et al., 2002). Its genome is 228,089 bp in size encoding 154 ORFs and has a G+C content of 42%. These ORFs are randomly distributed on both DNA strands with 45% clockwise orientation and 55% counterclockwise orientation. Later on, the genome of OrNV, the first discovered nudivirus, was partially sequenced (Wang et al., 2007a). The genome of the GbNV is 96,944 bp in length, has a G+C content of 28%, and contains 98 ORFs (Wang et al., 2007b). 58% of its ORFs are in clockwise distribution; 42% are in reverse direction (Wang et al., 2007b). HzNV-2, the close relative to HzNV-1, has also been sequenced and has a genome of 231,621 bp, only slightly longer than that of HzNV-1, with a G+C content of 42% identical to HzNV-1 (Wang et al., 2007c). HzNV-1 and HzNV-2 share 99% nucleotide sequence identity and encode similar numbers of ORFs (Burand, 2008). Recently, sequencing the complete genome of OrNV was successfully achieved by using DNA generated by multiple displacement amplification (MDA) (Wang et al., 2008). The OrNV genome is 127,615 bp in size and contains 139 ORFs and a G+C content of 42% (Wang et al., 2008); Wang and Jehle, unpublished). Sequencing of other nudivirus genomes such as the shrimp PmNV is ongoing; partial nucleotide sequences are already accessible in GenBank. Repetitive sequences (RS) were detected in all sequenced nudivirus genomes. They are variable in length and numbers and are distributed throughout the genome. They are homologous neither to each other within and between genomes, nor to those of other large dsDNA viruses, such as baculoviruses, SGHVs and WSSV. RS appear to be a universal feature of all large dsDNA viruses. 3.2. Gene content and function As shown in Table 1, there are 66, 34, and 33 homologous genes shared by OrNV and GbNV, OrNV and HzNV-1, and GbNV and HzNV-1, respectively, suggesting that OrNV and GbNV are more closely related to each other than to HzNV-1. All sequenced nudivirus genomes have 33 genes in common. Strikingly, 20 out of them are homologues of baculovirus core genes, which are present in all 48 baculovirus genomes that have been deposited in GenBank as of February 2009. All baculoviruses share 30 core genes, which play crucial role in baculovirus replication cycle and are the evolutionary marker genes for baculovirus identification, classification and phylogeny (Herniou et al., 2003; Herniou and Jehle,
2007; Jehle et al., 2006a; Jehle et al., 2006b; van Oers and Vlak, 2007). Surprisingly, one conserved nudivirus ORF is similar to the baculovirus polh/gran gene encoding the OB protein in Alpha-, Beta- and Gammabaculoviruses. Nine other ORFs are likely involved in DNA replication, DNA repair and recombination, and nucleotide metabolism; one is homologous to baculovirus iap-3 gene; two others are nudivirus-specific ORFs of unknown function. The conservation of 20 baculovirus core genes in nudiviruses strongly indicates that nudiviruses and baculoviruses are much more closely related to each other than to any other viruses known so far. Besides in nudiviruses, interestingly, homologues to baculovirus core genes were detected recently in two unassigned salivary gland hypertrophy viruses (SGHVs), infecting the house fly Musca domestica (MdSGHV) and the tsetse fly Glossina pallidipes (GpSGHV), respectively (Abd-Alla et al., 2008; Garcia-Maruniak et al., 2008). The 190 kbp genome of GpSGHV is composed of 160 ORFs and has a low G+C content of 28% (Abd-Alla et al., 2008), whereas the 124 kbp genome of MdSGHV contains 108 ORFs with a G+C content of 44% (Garcia-Maruniak et al., 2008). 37 MdSGHV ORFs are homologous to 42 GpSGHV ORFs (Garcia-Maruniak et al., 2009); GpSGHV and MdSGHV are phylogenetically closely related (Garcia-Maruniak et al., 2009). Accordingly, the new viral family ‘‘Hytrosaviridae” was proposed to classify SGHVs (Abd-Alla et al., 2009). In addition, several homologous baculovirus core genes could be also identified in the marine WSSV (Wang and Jehle, unpublished), suggesting that WSSV is evolutionarily related, albeit distantly, to baculoviruses, nudiviruses, and SGHVs. This finding provides crucial clues to dating back to the origin of arthropodspecific large DNA viruses. Most strikingly, nudiviruses, SGHVs and WSSV have the homologues to these four genes encoding peroral infectivity factors (p74, pif-1, pif-2 and pif-3) (Wang and Jehle, unpublished), which are conserved among all baculoviruses and are absolutely essential for successful peroral infection of insects. As midgut infection is the crucial first step in the pathogenesis of baculoviruses, PIFs may be important determinants of host range and virulence. Consequently, hypothesising a highly conserved interaction mode upon primary infection in baculoviruses, nudivirusees, SGHVs and WSSV seems to be plausible. However, only scattered information on the function of the PIF proteins has been delineated (Slack and Arif, 2007). Further deciphering of the molecular mechanisms of their key role in oral infection of invertebrate hosts will be crucial to understand host range, zoonotic behaviour, and epizootic or enzootic disease of these viruses. Additionally, nudiviruses and SGHVs also appear to share homologues of the
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193
191
RNA transcription apparatus of baculoviruses suggesting that these viruses use a similar mode of late gene transcription (Wang and Jehle, unpublished). The in vivo biochemical and biological function of the genes predicted in nudiviruses remains unknown. Only the occlusion body-encoding gene in PmNV has been molecularly identified (Chaivisuthangkura et al., 2008). 3.3. Gene order Gene order is poorly conserved in nudivirus genomes. OrNV and GbNV share a number of gene clusters comprising 2–7 collinearly arranged genes, distributed throughout their genomes (Fig. 2). In contrast, only two gene clusters were detected between OrNV and HzNV-1. However, a gene cluster of helicase, 19 kda, and/or lef-5 is present in all nudivirus genomes, which is similar to the conserved core gene cluster of four genes of helicase, 19 kda, 38 K and lef-5 is found in all baculoviruses (Herniou et al., 2003; Jehle and Backhaus, 1994). Hence, both core gene content and gene clustering strongly support the hypothesis of a common ancestor of nudiviruses and baculoviruses. 4. Phylogeny and evolution Members of nudiviruses possess interesting biological and molecular properties and show broad ‘‘ecological” and phylogenetic host range, making them ideal to study virus evolution. But it is only since their genomes have been recently sequenced and characterised that deeper insights into nudivirus evolutionary history became accessible. In the phylogenetic tree of large circular dsDNA viruses, nudiviruses are monophyletic (Fig. 3). HzNVs are close relatives and share a recent common ancestor with PmNV (Fig. 3) (Wang et al., 2007c); OrNV and GbNV were clustered in a single group and diverged from the common ancestor of PmNV and HzNVs. It is proposed that nudiviruses and baculoviruses are sister lineages, which diverged early from SGHVs and WSSV (Wang and Jehle, unpublished). The tree branching pattern is in agreement with gene content analyses revealing a decreasing number of gene homologues shared between nudiviruses, baculoviruses, SGHVs and WSSV. It also correctly reproduces our present-day picture of baculovirus phylogeny, with dipteran and hymenopteran NPVs as basal branches and two sister-groups of lepidopteran NPVs and GVs (Jehle et al., 2006a). The common ancestor of nudiviruses and baculoviruses did not date back to the ancient origin of arthropods and their evolution was likely shaped by the interaction between the viruses and their hosts and was driven by the specific ecological niches the hosts colonise. It is conceivable that these large dsDNA viruses derived from a marine ancestor virus.
Fig. 2. Gene parity plots of OrNV versus GbNV and HzNV-1 genomes, respectively. Each ORF is shown in a black square following the order from 1 to 139 on the x-axis (left to right) and from 1 to 98 for GbNV and 1 to 154 for HzNV-1 on the y-axis (up to down). ORFs with similarity fall inside the two axes, while ORFs without similarity appear on the outside of the axis. The gene cluster of helicase and 19 kda conserved in both nudiviruses and baculoviruses is marked in a dashed circle.
Fig. 3. Nudivirus phylogeny. The tree is adapted from (Wang and Jehle, unpublished) and was constructed by using the supermatrix method (de Queiroz and Gatesy, 2007), simultaneously analysing a set of conserved homologous genes present in nudiviruses, baculoviruses, SGHVs, and WSSV (Wang and Jehle, unpublished).
5. Classification Recently, the viral genus Nudivirus together with demarcation criteria and naming strategies has been proposed for classification of nudiviruses, which appears to be still reliable (Wang et al., 2007a,b,c). What needs to be reconsidered here is the criterion of OB formation. OB formation is a widespread phenomenon in several insect-infecting viral taxa, such as the Baculoviridae, the Entomopoxvirinae and the Cypovirus (Reoviridae) (Buller et al., 2005; Mertens et al., 2005). It seems to be a highly successful convergent adaptation of many insect viruses to persist outside the host. As mentioned above, clearly, some members of nudiviruses, if not all, do generate OBs. OB formation likely plays a less distinct ecological role in the life-cycle of nudiviruses than in that of baculoviruses. However, deeming nudiviruses as non-occluded viruses is not justified. Taking into account the important role of non-occluded virions in nudivirus enzootics, there is no linguistic disaccord in retaining the name nudivirus for these viruses. Another concern is their appropriate classification into a virus subfamily or family. Presently, nudiviruses comprise five tentative species, OrNV, GbNV, HzNV-1, HzNV-2, and PmNV. According to their similarities to baculoviruses, the formation of a subfamily ‘‘Nudivirinae” within the family Baculoviridae might be feasible. On the other hand, however, given their distinct biological and ecological features as well as their virion properties, the establishment of an independent family ‘‘Nudiviridae” within a new order ‘‘Baculovirales” along with the Baculoviridae seems also conceivable. The latter might be most pragmatic since the establishment of such an order may allow subsequent flexible integration of other ‘‘baculovirus-related” but highly diverged viruses, such as the proposed ‘‘Hytrosaviridae” or the Nimaviridae, without taxonomic re-definition of the family Baculoviridae. 6. Conclusions and perspectives The recent advances in nudivirus genome analyses clearly cast new lights on their biological properties as well as their phyloge-
192
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193
netic origin and evolution. Phylogenetically, nudiviruses represent a distinct lineage of large DNA viruses and are related to baculoviruses. Importantly, their evolutionary relationship to other large DNA viruses such as SGHVs and WSSV has been evidenced, paving the way for further exploring the divergent evolution of invertebrate-specific large dsDNA viruses. Recently, the groundbreaking findings by Bézier et al. (2009a,b) showing that bracoviruses, the symbiotic large DNA viruses of Hymenoptera, derived from an ancestral nudivirus, challenge our current understanding of how nudiviruses originated and evolved (see also in Bézier et al., 2009b). However, studying nudiviruses is still in its infancy. Among the more than 400 annotated nudivirus ORFs, only very few have been biochemically characterised. Little is known about their role in the virus infection and replication process. Hence, the functional characterisation of these genes, in particular of the conserved core genes, is urgent and will bring about a glimmer of light into the shadowy scientific existence of nudiviruses. Acknowledgments This paper was the result of a presentation on Comparative Genomics of DNA viruses at the 41st Annual Meeting of the Society for Invertebrate Pathology (University of Warwick, UK, August 3–7, 2008), for which we thank Elisabeth A. Herniou for the invitation to attend. We are indebted to Regina G. Kleespies and Alois M. Huger for providing the GbNV photos. We thank Monique M. van Oers, Just M. Vlak, Regina G. Kleespies, Alois M. Huger, Moslim B. Ramle, and Trevor Jackson for fruitful cooperation, and Adly M. M. AbdAlla, Alejandra Garcia-Maruniak, John P. Burand, and Jean-Michel Drezen for communications and discussions. Financial supports were provided through the research projects by the Deutsche Forschungsgemeinschaft (DFG Je245-7). References Abd-Alla, A.M.M., Cousserans, F., Parker, A.G., Jehle, J.A., Parker, N.J., Vlak, J.M., Robinson, A.S., Bergoin, M., 2008. Genome analysis of a Glossina pallidipes salivary gland hypertrophy virus reveals a novel, large, double-stranded circular DNA virus. J. Virol. 82, 4595–4611. Abd-Alla, A.M.M., Vlak, J.M., Bergoin, M., Maruniak, J.E., Parker, A., Burand, J.P., Jehle, J.A., Boucias, D.G., 2009. Hytrosaviridae: a proposal for classification and nomenclature of a new insect virus family. Arch. Virol. 154, 909–918. Bézier, A., Annaheim, M., Herbinière, J., Wetterwald, C., Gyapay, G., Bernard-Samain, S., Wincker, P., Roditi, I., Heller, M., Belghazi, M., Pfister-Wilhem, R., Periquet, G., Dupuy, C., Huguet, E., Volkoff, A.N., Lanzrein, B., Drezen, J.M., 2009a. Polydnaviruses of braconid wasps derive from an ancestral nudivirus. Science 323, 926–930. Bézier, A., Herbinière, J., Lanzrein, B., Drezen, J.M., 2009b. Polydnavirus hidden face: The genes producing virus particles of parasitic wasps. J. Invertebr. Pathol. 101, 194–203. Buller, R.M., Arif, B.M., Black, D.N., Dumbell, K.R., Esposito, J.J., Lefkowitz, E.J., McFadden, G., Moss, B., Mercer, A.A., Moyer, R.W., Skinner, M.A., Tripathy, D.N., 2005. Poxviridae. In: Fauquet, C.M., Mayo, M.A., Maniloff, J., Desselberger, U., Ball, L.A. (Eds.), Virus Taxonomy. Classification and Nomenclature of Viruses. Eighth Report of the International Committee on Taxonomy of Viruses. Elsevier, Academic Press, New York, pp. 117–133. Burand, J.P., 1998. Nudiviruses. In: Miller, L.K., Ball, L.A. (Eds.), The Insect Viruses. Plenum Press, New York, pp. 69–90. Burand, J.P., 2008. Insect viruses: nonoccluded. In: Mahy, B.W.J., Van Regenmortel, M.H.V. (Eds.), Encyclopedia of Virology. Elsevier, Oxford, pp. 144–148. Burand, J.P., Stiles, B., Wood, H.A., 1983. Structural and intracellular proteins of the nonoccluded baculovirus Hz-1. J. Virol. 46, 137–142. Chaivisuthangkura, P., Tawilert, C., Tejangkura, T., Rukpratanporn, S., Longyant, S., Sithigorngul, W., Sithigorngul, P., 2008. Molecular isolation and characterization of a novel occlusion body protein gene from Penaeus monodon nucleopolyhedrovirus. Virology 381, 261–267. Cheng, C.H., Liu, S.M., Chow, T.Y., Hsiao, Y.Y., Wang, D.P., Huang, J.J., Chen, H.H., 2002. Analysis of the complete genome sequence of the Hz-1 virus suggests that it is related to members of the Baculoviridae. J. Virol. 76, 9024–9034. Crawford, A.M., Sheehan, C., 1985. Replication of Oryctes baculovirus in cell culture: viral morphogenesis, infectivity and protein synthesis. J. Gen. Virol. 66, 529– 539. de Queiroz, A., Gatesy, J., 2007. The supermatrix approach to systematics. Trends Ecol. Evol. 22, 34–41.
Garcia-Maruniak, A., Maruniak, J.E., Farmerie, W., Boucias, D.G., 2008. Sequence analysis of a non-classified, non-occluded DNA virus that causes salivary gland hypertrophy of Musca domestica, MdSGHV. Virology 377, 184–196. Garcia-Maruniak, A., Abd-Alla, A.M.M., Salem, T.Z., Parker, A.G., Lietze, V.-U., van Oers, M.M., Maruniak, J.E., Kim, W., Burand, J.P., Cousserans, F., Robinson, A.S., Vlak, J.M., Bergoin, M., Boucias, D.G., 2009. Two viruses that cause salivary gland hypertrophy in Glossina pallidipes and Musca domestica are related and form a distinct phylogenetic clade. J. Gen. Virol. 90, 334–346. Granados, R.R., Nguyen, T., Cato, B., 1978. An insect cell line persistently infected with a baculovirus-like particle. Intervirology 10, 309–317. Hamm, J.J., Carpenter, J.E., Styer, E.L., 1996. Oviposition day effect on incidence of agonadal progeny of Helicoverpa zea (Lepidoptera: Noctuidae) infected with a virus. Ann. Entomol. Soc. Am. 56, 535–556. Herniou, E.A., Jehle, J.A., 2007. Baculovirus phylogeny and evolution. Curr. Drug Targets 8, 1043–1050. Herniou, E.A., Olszewski, J.A., Cory, J.S., O’Reilly, D.R., 2003. The genome sequence and evolution of baculoviruses. Annu. Rev. Entomol. 48, 211–234. Herzog, G.A., Phillips, J.R., 1982. Manifestation of an abnormal reproductive system in a laboratory strain of the bollworm Heliothis zea. J. Ga. Entomol. Soc. 17, 506. Huger, A.M., 1966. A virus disease of the Indian rhinoceros beetle, Oryctes rhinoceros (Linnaeus), caused by a new type of insect virus, Rhabdionvirus oryctes gen. n., sp. n. J. Invertebr. Pathol. 8, 38–51. Huger, A.M., 1985. A new virus disease of crickets (Orthoptera: Gryllidae) causing macronucleosis of fatbody. J. Invertebr. Pathol. 45, 108–111. Huger, A.M., Krieg, A., 1991. Baculoviridae. Nonoccluded baculoviruses. In: Adams, J.R., Bonami, J.R. (Eds.), Atlas of Invertebrate Viruses. CRC Press, Inc., Boca Raton, pp. 287–319. Jehle, J.A., Backhaus, H., 1994. Genome organization of the DNA-binding protein gene region of Cryptophlebia leucotreta granulosis virus is closely related to that of nuclear polyhedrosis viruses. J. Gen. Virol. 75, 1815–1820. Jehle, J.A., Blissard, G.W., Bonning, B.C., Cory, J.S., Herniou, E.A., Rohrmann, G.F., Theilmann, D.A., Thiem, S.M., Vlak, J.M., 2006a. On the classification and nomenclature of baculoviruses: a proposal for revision. Arch. Virol. 151, 1257– 1266. Jehle, J.A., Lange, M., Wang, H., Hu, Z., Wang, Y., Hauschild, R., 2006b. Molecular identification and phylogenetic analysis of baculoviruses from Lepidoptera. Virology 346, 180–193. Johnson, P.T., Lightner, D.V., 1988. Rod-shaped nuclear viruses of crustaceans: gutinfecting species. Dis. Aquat. Org. 5, 123–141. Lightner, D.V., Redman, R.M., 1981. A baculovirus-caused disease of the penaeid shrimp, Penaeus monodon. J. Invertebr. Pathol. 38, 299–302. Lightner, D.V., Redman, R.M., Bell, T.A., 1983. Observations on the geographic distribution, pathogenesis and morphology of the baculovirus from Penaeus monodon Fabricius. Aquaculture 32, 209–233. Mari, J., Bonami, J.-R., Poulos, B., Lightner, D., 1993. Preliminary characterization and partial cloning of the genome of a baculovirus from Penaeus monodon (PmSNPV = MBV). Dis. Aquat. Org. 16, 207–215. Mertens, P.P.C., Rao, S., Zhou, Z.H., 2005. Reoviridae – Cypovirus. In: Fauquet, C.M., Mayo, M.A., Maniloff, J., Desselberger, U., Ball, L.A. (Eds.), Virus Taxonomy. Classification and Nomenclature of Viruses. Eighth Report of the International Committee on Taxonomy of Viruses. Elsevier Academic Press, New York, pp. 522–533. Payne, C.C., 1974. The isolation and characterization of a virus from Oryctes rhinoceros. J. Gen. Virol. 25, 105–116. Quiot, J.-M., Monsarrat, P., Meynadler, G., Croizier, G., Vago, C., 1973. Infection des cultures cellulaires de Coléoptères par le ‘virus Oryctes’. CR. Acad. Sci. Ser. D 276, 3229–3231. Raina, A.K., Adams, J.R., 1995. Gonad-specific virus of corn earworm. Nature 374, 770. Raina, A.K., Lupiani, B., 2006. Acquisition, persistence, and species susceptibility of the Hz-2V virus. J. Invertebr. Pathol. 93, 71–74. Raina, A.K., Adams, J.R., Lupiani, B., Lynn, D.E., Kim, W., Burand, J.P., Dougherty, E.M., 2000. Further characterization of the gonad-specific virus of corn earworm, Helicoverpa zea. J. Invertebr. Pathol. 76, 6–12. Rohrmann, G.F., 2008. Baculovirus Molecular Biology. National Library of Medicine (US), NCBI, Bethesda (MD). Slack, J., Arif, B.M., 2007. The baculoviruses occlusion-derived virus: virion structure and function. Adv. Virus Res. 69, 99–165. van Hulten, M.C., Witteveldt, J., Peters, S., Kloosterboer, N., Tarchini, R., Fiers, M., Sandbrink, H., Lankhorst, R.K., Vlak, J.M., 2001. The white spot syndrome virus DNA genome sequence. Virology 286, 7–22. van Oers, M.M., Vlak, J.M., 2007. Baculovirus genomics. Curr. Drug Targets 8, 1051– 1068. Vlak, J.M., Bonami, J.R., Flegel, T.W., Kou, G.H., Lightner, D.V., Lo, C.F., Loh, P.C., Walker, P.W., 2005. Nimaviridae. In: Fauquet, C.M., Mayo, M.A., Maniloff, J., Desselberger, U., Ball, L.A. (Eds.), Virus Taxonomy. Classification and Nomenclature of Viruses. Eighth Report of the International Committee on Taxonomy of Viruses. Elsevier, Academic Press, New York, pp. 187–192. Wang, Y., van Oers, M.M., Crawford, A.M., Vlak, J.M., Jehle, J.A., 2007a. Genomic analysis of Oryctes rhinoceros virus reveals genetic relatedness to Heliothis zea virus 1. Arch. Virol. 152, 519–531. Wang, Y., Kleespies, R.G., Huger, A.M., Jehle, J.A., 2007b. The genome of Gryllus bimaculatus nudivirus indicates an ancient diversification of baculovirus-related nonoccluded nudiviruses of insects. J. Virol. 81, 5395–5406. Wang, Y., Burand, J.P., Jehle, J.A., 2007c. Nudivirus genomics: diversity and classification. Virologica Sinica 22, 128–136.
Y. Wang, J.A. Jehle / Journal of Invertebrate Pathology 101 (2009) 187–193 Wang, Y., Kleespies, R.G., Ramle, M.B., Jehle, J.A., 2008. Sequencing of the large dsDNA genome of Oryctes rhinoceros nudivirus using multiple displacement amplification of nanogram amounts of virus DNA. J. Virol. Methods 152, 106–108.
193
Yang, F., He, J., Lin, X., Li, Q., Pan, D., Zhang, X., Xu, X., 2001. Complete genome sequence of the shrimp white spot bacilliform virus. J. Virol. 75, 11811– 11820.