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Light driven reactions in model algae
Accepted Manuscript Title: Light driven reactions in model algae Author: Maria Mittag PII: DOI: Reference:
S0176-1617(17)30192-X http://dx.doi.org/doi:10.1016/j.jplph.2017.07.010 JPLPH 52630
To appear in: Author: Christian Wilhelm PII: DOI: Reference:
S0176-1617(17)30192-X http://dx.doi.org/doi:10.1016/j.jplph.2017.07.010 JPLPH 52630
To appear in:
Please cite this article as: Wilhelm Christian.Light driven reactions in model algae.Journal of Plant Physiology http://dx.doi.org/10.1016/j.jplph.2017.07.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Editorial Light driven reactions in model algae *Maria Mittag Friedrich Schiller University Jena, Jena, Germany Christian Wilhelm University of Leipzig, Leipzig, Germany *Corresponding author:
E-mail addresses: *[email protected] (M.Mittag), [email protected] (C. Wilhelm)
This special issue is dedicated to light driven reactions in model algae. Cyanobacteria and eukaryotic unicellular phototrophs (microalgae) contribute roughly to 50% of CO 2 fixation on Earth (Field et al., 1998). However, light is not only a source of energy for algal photosynthesis, it also delivers information to trigger behavioral and developmental responses and it entrains their circadian clocks under control of sensory photoreceptors. In this issue, the papers include the whole umbrella of light reactions from the biophysics of the photoreceptors to the physiological read out documented by growth efficiency and acclimation reactions. A broad view on members of light perception could be achieved, because in the past years, numerous sequences of algal genomes became available and allowed to study light driven reactions at multiple levels including genetic modification of known photosensors and the discovery of new ones. Diversifications of phytochrome photoreceptors in cyanobacteria and eukaryotic algae became thus obvious (Rockwell and Lagarias, 2017) as well as the widespread, but multitasking cryptochrome/photolyase family (Fortunato et al., 2015). For a detailed understanding of sensory photoreceptors, it is important to study not only their biophysical properties based on heterologously expressed proteins, but also to combine these studies with in-vivo investigations on their biological function. For this purpose, algal model systems became attractive which can be transformed and for which necessary molecular tools are available. Thereby, new technologies for knock-down or knock-out of the genes of interest are also needed. For these reasons, biological functions of algal photoreceptors have been mainly investigated in the green 1
biflagellate alga Chlamydomonas reinhardtii and in the pennate diatom Phaeodactylum tricornutum where many molecular tools exist and genome sequences are available (Merchant et al., 2007; Bowler et al., 2008). Interestingly, both algae bear a large (> 20) and diverse repertoire as well as new types of photoreceptors going far beyond those found in higher plants. This may reflect the different habitats of algae (freshwater and moist soil in case of C. reinhardtii and marine environment for P. tricornutum), including frequent changes in light conditions, but may also point to phylogenetic selection processes. Both algae are being exposed to different light qualities and intensities throughout the water column as well as throughout the day-night cycles of the different seasons. The motile biflagellate C. reinhardtii bears multiple types of photoreceptors, including several cryptochromes. Its genome encodes not only a classical plant cryptochrome (pCRY, formerly CPH1), but also an animal-like CRY (CraCRY) beside two so-called CRY-DASH proteins (Beel et al., 2012). Variances in the presence or absence of the different types of CRYs (plant, plant-like, animal-like and CRY-DASH) depend indeed on the species, as for example in the green algae (Fortunato et al., 2015; Kottke et al., this issue). In C. reinhardtii, a phototropin is also present, as well as a UV-receptor and several channelrhodopsins, some of which belong to the mostly unexplored group of Histidin-kinase rhodopsins (HKRs), where the light sensing domain is covalently linked to signal-transduction modules and sometimes to a Cterminal guanylyl-cyclase effector (Kateriya et al., 2004; Hegemann, 2008; Tilbrook et al., 2016). However, the typical red light receptor phytochrome is not encoded by C. reinhardtii (Merchant et al., 2007). In P. tricornutum, phytochrome is present (Fortunato et al., 2016) as well as novel-type LOV-domain bearing receptors that also contain a transcription factor bZip domain, the Aureochromes (AUREO1-4) (Schellenberger et al., 2013b). Interestingly, P. tricornutum lacks a typical plant CRY, but the alga has a plant-like CRY (CryP; Juhas et al., 2014) beside other CRYs including a member close to CraCRY, the so called CPF1 (Coesel et al., 2009). In the recent years, major achievements towards the properties of several of the above-mentioned photoreceptors have been made and the new findings have been used for establishing optogenetic tools as with microbial rhodopsins (Hegemann and Nagel, 2013; Govorunova et al., 2017). In this Special issue of Journal of Plant Physiology, we do not concentrate on optogenetic applications. Instead, we focus on the diversity, biophysical properties and biological functions of exemplary algal 2
photoreceptors and highlight novel findings that emerged in the recent years in these fields. Thus, an allosteric regulation of AUREOs was observed (Banjeree et al., 2016) and red light sensitivity of CraCRY in addition to blue-light as well as the underlying amino acid(s) relevant for this spectral response (Beel et al., 2012; Oldemeyer et al., 2016). The broad spectral response has been also found for CryP, based in both cases on the neutral radical form of flavin (Juhas et al., 2014). Moreover, the novel HKR1 covalently linked to a C-terminal guanyl- cyclase effector was shown to exhibit a UVAblue light switch (Luck et al., 2012). In addition to the biophysical properties, functional analyses of several of these photoreceptors were performed based on knock-down or knock-out mutants generated by specialized methods such as broad scale insertional mutagenesis followed by selective PCR, TALEN or Zinc Finger Nuclease approaches. They revealed central roles of specific AUREOs in the cell cycle and high light acclimation in the diatom (Huysman et al., 2013; Schellenberger et al.., 2013b), key roles of aCRY and pCRY in the sexual cycle of C. reinhardtii as positive regulators of germination in addition to phototropin and as negative regulators in contrast to phototropin, for gametogenesis (Müller et al., 2017; Zou et al., 2017). Moreover, pCRY was shown to be linked not only to circadian input but it seems also connected to the oscillatory system (Müller et al., 2017). Intriguingly, it was found with a Chlamydomonas phototropin knock-out mutant that this photoreceptor is directly linked to photosynthesis and photoprotection via a specific member of the light harvesting complex proteins (LHCSR3) (Petroutsos et al., 2016). An influence of some photoreceptors such as CraCRYor CryP on the expression of certain LHCs was also found (Beel et al., 2012; Juhas et al., 2014). LHC proteins and their pigmentation in algae are complex. LHC expression varies under different light intensities and qualities. The application of RNA-Seq (Weber, 2015) and proteome approaches have paved a way to study broad scale changes in the RNA and protein levels of LHCs (e.g.; Neilson et al., this issue). Especially at the protein level, new insights into complex formation and stoichiometry of members of these complexes can be achieved by applying functional proteomics (Joshi-Deo et al., 2010; Schellenberger et al., 2013a). In this issue, the results of a research network (FOR1261) funded by the German Research Foundation are presented in the light of international progress in the field. Several of the underlying topics of FOR1261 have been done in collaboration 3
with international researchers (for example, Beel et al., 2012; Luck et al., 2012; Huysman et al., 2013; Petroutsos et al., 2016; Müller et al., 2017). Moreover, this issue does not only present review papers but also includes original contributions from authors outside the German research network (see the paper by Neilson et al. and by Rockwell and Lagarias, this issue), documenting that the field of light driven reactions in algae is a worldwide emerging area of scientific activity. Three different types of papers are collected: (1) Review papers, (2) methodological papers and (3) original research contributions. The reader will find a review on the cryptochrome family in diatoms (König et al. this issue), on the diversity of cryptochromes in green algae (Kottke et al. this issue) and on aureochromes only found in chromalveolates (Kroth et al. this issue). A forth survey concentrates on the structural and mechanistic similarities and differences of blue light receptors exemplified for the cryptochromes and auroechromes (Essen et al. this issue). Another review paper by Rockwell and Lagarias (this issue) including also original work, concentrates on Ferredoxindependent bilin reductases playing a crucial role in the biosynthesis of phytochrome photoreceptors. Moreover, Luck et al. (this issue) present the state of the art of Histidine kinase rhodopsin1, how it works and how it is regulated. The methodological orientated papers refer to the recent progress in “omics” approaches in algal sensory systems. Büchel et al. (this issue) report the present knowledge on the application of functional proteomics to investigate light harvesting proteins in diatoms, which possess an unusual richness in this gene family, at different light intensities and light qualities. Rademacher et al. (this issue) show how RNA-seq can help to understand the transcriptomic response of extremophilic cells in the case of the red alga Cyanidioschyzon merolae to changing CO2 conditions. A similar methodological approach is presented for the chlorarachniophyte algae Bigelowiella natans (Neilson et al., this issue), and studies its light harvesting antenna system under different light intensities. Finally, the issue includes original work by Mann et al. (this issue) showing that two of the four different
aureochromes are functionally not redundant,
emphasizing that the large families of photoreceptors still wait to be further explored in the next future. References Banerjee, A., Herman, E., Serif, M., Maestre-Reyna, M., Hepp, S., Pokorny, R., Kroth, P.G., Essen, L.O., Kottke, T., 2016. Allosteric communication between 4
DNA-binding and light-responsive domains of diatom class I aureochromes. Nucleic Acids Res. 244, 5957-5970. doi: 10.1093/nar/gkw420. Beel, B., Prager, K., Spexard, M., Sasso, S., Weiss, D., Müller, N., Heinnickel, M., Dewez, D., Ikoma, D., Grossman, A.R., Kottke, T., Mittag, M., 2012. A flavin binding cryptochrome photoreceptor responds to both blue and red light in Chlamydomonas reinhardtii. Plant Cell 24, 2992-3008. doi: 10.1105/tpc.112.098947. Büchel, C., Wilhelm, C., Wagner, V., Mittag, M., 2017. Functional proteomics of lightharvesting complex proteins under varying light-conditions in diatoms. J. Plant Physiol. Bowler, C., Allen, A.E., Badger, J.H., Grimwood, J., Jabbari, K., Kuo, A. et al., 2008. The Phaeodactylum genome reveals the evolutionary history of diatom genomes. Nature 456, 239–244. http://dx.doi: 10.1038/nature07410. Coesel S, Mangogna M, Ishikawa T, Heijde M, Rogato A, Finazzi G, Todo T, Bowler C, Falciatore A (2009) Diatom PtCPF1 is a new cryptochrome/photolyase family member with DNA repair and transcription regulation activity. EMBO Rep 10: 655-661. doi: 10.1038/embor.2009.59. Essen, L.-O., Franz, S., Banerjee, A., 2017. Structural and evolutionary aspects of algal blue light receptors of the cryptochrome and aureochrome type. J. Plant Physiol. Field, C.B., Behrenfeld, M.J., Randerson, J.T., Paul Falkowski P., 1998. Primary production of the biosphere: Integrating terrestrial and oceanic components. Science 281, 237-240. http://dx.doi: 10.1126/science.281.5374.237. Fortunato, A.E., Annunziata, R., Jaubert, M., Bouly, J.P., Falciatore, A. 2015. Dealing with light: the widespread and multitasking cryptochrome/photolyase family in photosynthetic organisms. J. Plant Physiol. 172, 42-54. doi: 10.1016/j.jplph.2014.06.011. Fortunato, A.E., Jaubert, M., Enomoto, G., Bouly, J.P., Raniello, R., Thaler, M., Malviya, S., Bernardes, J.S., Rappaport, F., Gentili, B. et al., 2016. Diatom phytochromes reveal the existence of far-red-light-based sensing in the ocean. Plant Cell. 28, 616-28. doi: 10.1105/tpc.15.00928. Govorunova, E.G., Sineshchekov, O.A., Li, H., Spudich, J.L., 2017. Microbial rhodopsins: Diversity, mechanisms, and optogenetic applications. Annu. Rev. Biochem. doi: 10.1146/annurev-biochem-101910-144233. [Epub ahead of print] 5
Hegemann, P., 2008. Algal sensory photoreceptors. Annu. Rev. Plant Biol. 59, 167189. doi: 10.1146/annurev.arplant.59.032607.092847. Hegemann, P., Nagel., G., 2013. From channelrhodopsins to optogenetics.EMBO Mol. Med. 5, 173-176. doi: 10.1002/emmm.201202387. Huysman, M.J., Fortunato, A.E., Matthijs, M., Schellenberger Costa, B., Vanderhaeghen, R., Van den Daele, H., Sachse, M., Inze, D., Bowler, C., Kroth, P.G., Wilhelm, C., Falciatore, A., Vyverman, W., De Veylder, L., 2013. AUREOCHROME1a-mediated induction of the diatom-specific cyclin dsCYC2 controls the onset of cell division in diatoms (Phaeodactylum tricornutum). Plant Cell 25, 215-228. doi: 10.1105/tpc.112.106377. Joshi-Deo, J., Schmidt, M., Gruber, A., Weisheit, W., Mittag, M., Kroth, P.G., Büchel, C., 2010. Characterization of a trimeric light-harvesting complex in the diatom Phaeodactylum tricornutum built of FcpA and FcpE proteins. J. Exp. Bot. 61, 3079–3087. http://dx.doi: 10.1093/jxb/erq136. Juhas, M., von Zadow, A., Spexard, M., Schmidt, M., Kottke, T., Büchel, C., 2014. A novel cryptochrome in the diatom Phaeodactylum tricornutum influences the regulation of light-harvesting protein levels. FEBS J. 281, 2299-2311. doi: 10.1111/febs.12782 Kateriya, S., Nagel, G., Bamberg, E., Hegemann, P., 2004. Vision in single-celled algae. New Physiol. Sci. 19, 133-137. PMID:15143209. König, S., Juhas. M., Jäger, S., Kottke, T., Büchel, C., 2017. The cryptochrome – photolyase protein family in diatoms. J Plant Physiol. Kottke, T., Oldemeyer, S., Wenzel, S., Zou, Y., Mittag, M., 2017. Cryptochrome photoreceptors in green algae: Unexpected versatility of mechanisms and functions. J. Plant Physiol. Kroth, P.G., Wilhelm, C., Kottke, T., 2017. An update on aureochromes: Phylogeny – Mechanism – Function. J. Plant Physiol. Luck, M., Mathes, T., Bruun, S., Fudim, R., Hagedorn, R., Tran Nguyen, T.M., Kateriya, S., Kennis, J.T., Hildebrandt, P., Hegemann, P., 2012. A photochromic histidine kinase rhodopsin (HKR1) that is bimodally switched by ultraviolet and blue light. J. Biol. Chem. 287, 40083-40090. doi: 10.1074/jbc.M112.401604. Luck, M., Hegemann, P., 2017. The four dark states of the Chlamydomonas sensory photoreceptor histidine kinase rhodopsin 1. J Plant Physiol.
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Mann, M., Serif, S., Jakob, T., Kroth, P.G., Wilhelm, C., 2017. PtAUREO1a and PtAUREO1b knockout mutants of the diatom Phaeodactylum tricornutum are blocked in photoacclimation to blue light. J Plant Physiol. Merchant, S.S., Prochnik, S.E., Vallon, O., Harris, E.H., Karpowicz, S.J., Witman, G.B., Terry, A., Salamov, A., Fritz-Laylin, L.K., Maréchal-Drouard, L., et al. 2007. The evolution of key animal and plant functions is revealed by analysis of the Chlamydomonas genome. Science 318, 245-250. doi: 10.1126/science.1143609. Müller, N., Wenzel, S., Zou, Y., Künzel, S., Sasso, S., Weiß, D., Prager, K., Grossman, A.R., Kottke, T., Mittag, M., 2017. A plant cryptochrome controls key features of the Chlamydomonas circadian clock and its life cycle. Plant Physiol. 174, 185-201. doi: 10.1104/pp.17.00349. Neilson, J.A.D., Rangsrikitphoti, P., Durnford, D.G., 2017. Evolution and regulation of Bigelowiella natans light-harvesting antenna system. J Plant Physiol. Oldemeyer, S., Franz, S., Wenzel, S., Essen, L.O., Mittag, M., Kottke, T., 2016. Essential role of an unusually long-lived tyrosyl radical in the response to red light of the animal-like Cryptochrome aCRY. J. Biol. Chem. 291, 14062-14071. doi: 10.1074/jbc.M116.726976. Petroutsos, D., Tokutsu, R., Maruyama, S., Flori, S., Greiner, A., Magneschi, L., Cusant, L., Kottke, T., Mittag, M., Hegemann, P., et al. 2016. A blue light photoreceptor mediates the feedback regulation of photosynthesis. Nature 537, 563-566. doi: 10.1038/nature19358. Rademacher, N., Wrobel, T.J., Rossoni, A.W., Kurz, S., Bräutigam, A., Weber, A.P.M., Eisenhut, M., 2017. Transcriptional response of the extremophile red alga Cyanidioschyzon merolae to changes in CO2 concentrations. J. Plant Physiol. Rockwell, N.C., Lagarias, J.C., 2017. Phytochrome diversification in cyanobacteria and eukaryotic algae. Curr Opin Plant Biol. 37, 87-93. doi: 10.1016/j.pbi.2017.04.003. Rockwell, N.C., Lagarias, J.C., 2017. Ferredoxin-dependent bilin reductases in eukaryotic algae: ubiquity and diversity J. Plant Physiol. Schellenberger Costa, B., Jungandreas, A., Jakob, T., Weisheit, W., Mittag, M., Wilhelm, C., 2013a. Blue light is essential for high light acclimation and photoprotection in the diatom Phaeodactylum tricornutum. J. Exp. Bot. 64, 483493. http://dx.doi: 10.1093/jxb/ers340. 7
Schellenberger Costa, B., Sachse, M., Jungandreas, A., Bartulos, C.R., Gruber, A., Jakob, T., Kroth, P.G., Wilhelm, C. 2013b. Aureochrome 1a Is involved in the photoacclimation of the diatom Phaeodactylum tricornutum. PLoS ONE 8, e74451. doi: 10.1371/journal.pone.0074451. Tilbrook, K., Dubois, M., Crocco, C.D., Yin, R., Chappius, R., Allorent, G., SchmidSiegert, E., Goldschmidt-Clermont, M., Ulm, R., 2016. UV-B perception and acclimation in Chlamydomonas reinhardtii. Plant Cell 28, 966-983. doi: 10.1105/tpc.15.00287. Weber, A.P.M., 2015. Discovering new biology through RNA-Seq. Plant Physiol. 169, 1524-1531. doi: 10.1104/pp.15.01081. Zou, Y., Wenzel, S., Müller, N., Prager, K., Jung, E.M., Kothe, E., Kottke, T., Mittag, M., 2017. An animal-like cryptochrome controls the Chlamydomonas sexual cycle. Plant Physiol. DOI: 10.1104/pp.17.00493
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S0176-1617(17)30192-X http://dx.doi.org/doi:10.1016/j.jplph.2017.07.010 JPLPH 52630
To appear in: Author: Christian Wilhelm PII: DOI: Reference:
S0176-1617(17)30192-X http://dx.doi.org/doi:10.1016/j.jplph.2017.07.010 JPLPH 52630
To appear in:
Please cite this article as: Wilhelm Christian.Light driven reactions in model algae.Journal of Plant Physiology http://dx.doi.org/10.1016/j.jplph.2017.07.010 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting proof before it is published in its final form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.
Editorial Light driven reactions in model algae *Maria Mittag Friedrich Schiller University Jena, Jena, Germany Christian Wilhelm University of Leipzig, Leipzig, Germany *Corresponding author:
E-mail addresses: *[email protected] (M.Mittag), [email protected] (C. Wilhelm)
This special issue is dedicated to light driven reactions in model algae. Cyanobacteria and eukaryotic unicellular phototrophs (microalgae) contribute roughly to 50% of CO 2 fixation on Earth (Field et al., 1998). However, light is not only a source of energy for algal photosynthesis, it also delivers information to trigger behavioral and developmental responses and it entrains their circadian clocks under control of sensory photoreceptors. In this issue, the papers include the whole umbrella of light reactions from the biophysics of the photoreceptors to the physiological read out documented by growth efficiency and acclimation reactions. A broad view on members of light perception could be achieved, because in the past years, numerous sequences of algal genomes became available and allowed to study light driven reactions at multiple levels including genetic modification of known photosensors and the discovery of new ones. Diversifications of phytochrome photoreceptors in cyanobacteria and eukaryotic algae became thus obvious (Rockwell and Lagarias, 2017) as well as the widespread, but multitasking cryptochrome/photolyase family (Fortunato et al., 2015). For a detailed understanding of sensory photoreceptors, it is important to study not only their biophysical properties based on heterologously expressed proteins, but also to combine these studies with in-vivo investigations on their biological function. For this purpose, algal model systems became attractive which can be transformed and for which necessary molecular tools are available. Thereby, new technologies for knock-down or knock-out of the genes of interest are also needed. For these reasons, biological functions of algal photoreceptors have been mainly investigated in the green 1
biflagellate alga Chlamydomonas reinhardtii and in the pennate diatom Phaeodactylum tricornutum where many molecular tools exist and genome sequences are available (Merchant et al., 2007; Bowler et al., 2008). Interestingly, both algae bear a large (> 20) and diverse repertoire as well as new types of photoreceptors going far beyond those found in higher plants. This may reflect the different habitats of algae (freshwater and moist soil in case of C. reinhardtii and marine environment for P. tricornutum), including frequent changes in light conditions, but may also point to phylogenetic selection processes. Both algae are being exposed to different light qualities and intensities throughout the water column as well as throughout the day-night cycles of the different seasons. The motile biflagellate C. reinhardtii bears multiple types of photoreceptors, including several cryptochromes. Its genome encodes not only a classical plant cryptochrome (pCRY, formerly CPH1), but also an animal-like CRY (CraCRY) beside two so-called CRY-DASH proteins (Beel et al., 2012). Variances in the presence or absence of the different types of CRYs (plant, plant-like, animal-like and CRY-DASH) depend indeed on the species, as for example in the green algae (Fortunato et al., 2015; Kottke et al., this issue). In C. reinhardtii, a phototropin is also present, as well as a UV-receptor and several channelrhodopsins, some of which belong to the mostly unexplored group of Histidin-kinase rhodopsins (HKRs), where the light sensing domain is covalently linked to signal-transduction modules and sometimes to a Cterminal guanylyl-cyclase effector (Kateriya et al., 2004; Hegemann, 2008; Tilbrook et al., 2016). However, the typical red light receptor phytochrome is not encoded by C. reinhardtii (Merchant et al., 2007). In P. tricornutum, phytochrome is present (Fortunato et al., 2016) as well as novel-type LOV-domain bearing receptors that also contain a transcription factor bZip domain, the Aureochromes (AUREO1-4) (Schellenberger et al., 2013b). Interestingly, P. tricornutum lacks a typical plant CRY, but the alga has a plant-like CRY (CryP; Juhas et al., 2014) beside other CRYs including a member close to CraCRY, the so called CPF1 (Coesel et al., 2009). In the recent years, major achievements towards the properties of several of the above-mentioned photoreceptors have been made and the new findings have been used for establishing optogenetic tools as with microbial rhodopsins (Hegemann and Nagel, 2013; Govorunova et al., 2017). In this Special issue of Journal of Plant Physiology, we do not concentrate on optogenetic applications. Instead, we focus on the diversity, biophysical properties and biological functions of exemplary algal 2
photoreceptors and highlight novel findings that emerged in the recent years in these fields. Thus, an allosteric regulation of AUREOs was observed (Banjeree et al., 2016) and red light sensitivity of CraCRY in addition to blue-light as well as the underlying amino acid(s) relevant for this spectral response (Beel et al., 2012; Oldemeyer et al., 2016). The broad spectral response has been also found for CryP, based in both cases on the neutral radical form of flavin (Juhas et al., 2014). Moreover, the novel HKR1 covalently linked to a C-terminal guanyl- cyclase effector was shown to exhibit a UVAblue light switch (Luck et al., 2012). In addition to the biophysical properties, functional analyses of several of these photoreceptors were performed based on knock-down or knock-out mutants generated by specialized methods such as broad scale insertional mutagenesis followed by selective PCR, TALEN or Zinc Finger Nuclease approaches. They revealed central roles of specific AUREOs in the cell cycle and high light acclimation in the diatom (Huysman et al., 2013; Schellenberger et al.., 2013b), key roles of aCRY and pCRY in the sexual cycle of C. reinhardtii as positive regulators of germination in addition to phototropin and as negative regulators in contrast to phototropin, for gametogenesis (Müller et al., 2017; Zou et al., 2017). Moreover, pCRY was shown to be linked not only to circadian input but it seems also connected to the oscillatory system (Müller et al., 2017). Intriguingly, it was found with a Chlamydomonas phototropin knock-out mutant that this photoreceptor is directly linked to photosynthesis and photoprotection via a specific member of the light harvesting complex proteins (LHCSR3) (Petroutsos et al., 2016). An influence of some photoreceptors such as CraCRYor CryP on the expression of certain LHCs was also found (Beel et al., 2012; Juhas et al., 2014). LHC proteins and their pigmentation in algae are complex. LHC expression varies under different light intensities and qualities. The application of RNA-Seq (Weber, 2015) and proteome approaches have paved a way to study broad scale changes in the RNA and protein levels of LHCs (e.g.; Neilson et al., this issue). Especially at the protein level, new insights into complex formation and stoichiometry of members of these complexes can be achieved by applying functional proteomics (Joshi-Deo et al., 2010; Schellenberger et al., 2013a). In this issue, the results of a research network (FOR1261) funded by the German Research Foundation are presented in the light of international progress in the field. Several of the underlying topics of FOR1261 have been done in collaboration 3
with international researchers (for example, Beel et al., 2012; Luck et al., 2012; Huysman et al., 2013; Petroutsos et al., 2016; Müller et al., 2017). Moreover, this issue does not only present review papers but also includes original contributions from authors outside the German research network (see the paper by Neilson et al. and by Rockwell and Lagarias, this issue), documenting that the field of light driven reactions in algae is a worldwide emerging area of scientific activity. Three different types of papers are collected: (1) Review papers, (2) methodological papers and (3) original research contributions. The reader will find a review on the cryptochrome family in diatoms (König et al. this issue), on the diversity of cryptochromes in green algae (Kottke et al. this issue) and on aureochromes only found in chromalveolates (Kroth et al. this issue). A forth survey concentrates on the structural and mechanistic similarities and differences of blue light receptors exemplified for the cryptochromes and auroechromes (Essen et al. this issue). Another review paper by Rockwell and Lagarias (this issue) including also original work, concentrates on Ferredoxindependent bilin reductases playing a crucial role in the biosynthesis of phytochrome photoreceptors. Moreover, Luck et al. (this issue) present the state of the art of Histidine kinase rhodopsin1, how it works and how it is regulated. The methodological orientated papers refer to the recent progress in “omics” approaches in algal sensory systems. Büchel et al. (this issue) report the present knowledge on the application of functional proteomics to investigate light harvesting proteins in diatoms, which possess an unusual richness in this gene family, at different light intensities and light qualities. Rademacher et al. (this issue) show how RNA-seq can help to understand the transcriptomic response of extremophilic cells in the case of the red alga Cyanidioschyzon merolae to changing CO2 conditions. A similar methodological approach is presented for the chlorarachniophyte algae Bigelowiella natans (Neilson et al., this issue), and studies its light harvesting antenna system under different light intensities. Finally, the issue includes original work by Mann et al. (this issue) showing that two of the four different
aureochromes are functionally not redundant,
emphasizing that the large families of photoreceptors still wait to be further explored in the next future. References Banerjee, A., Herman, E., Serif, M., Maestre-Reyna, M., Hepp, S., Pokorny, R., Kroth, P.G., Essen, L.O., Kottke, T., 2016. Allosteric communication between 4
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