Wild relatives

Wild relatives

research news Seeing red and going nuclear Sakamoto, K. and Nagatani, A. (1996) Nuclear localization activity of phytochrome B, Plant J. 10, 859-868...

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Seeing red and going nuclear Sakamoto, K. and Nagatani, A. (1996) Nuclear localization activity of phytochrome B, Plant J. 10, 859-868

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Antibodies raised to CRYlWere used ~; check thatthe sealby vari~ ous by4 mutant alleles were consistent with the sizes bysequence sis; This Confirmed that the antibodies were specific to CRY1, and also that CRY1 is ~ soluble protein that is uniformly expressed throughout the plant. Overexpression o f CRY1 using the cauliflowermosaicvi~s35S in traasgenic plants resuItedin an apparent over': to blue light (i.e.the amount Of -light to inhibit hypocotyl growth was much tess for the transgenic plants than the wild-type plants). The transgenic plants were-aIso much Smaller, With shorter , ir~orescences and roots, Suggesting that CRY1 acts to inhibit cell expansion in all tissues. Another of the transgenic

:of c y a n i n : ~ ~ r e s p o n s e to b l u e light+. Conversely. it has been shown that hy4 mutants accumulate, less: anthocyanin than:~d:type plshf~: ~ Of the expression o f chalcone ~(a~key enzyme in the synthesis pathway} revealed that levels of its mRNA were. higher: in :plants CRYt:. Thus, it appears that the enhances gene expr well as rego .expansiOn.-:: . .::v -'/ ::!~:~.~

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© 1997 Elsevier Science Ltd

Phytochrome~are photoreceptors involved in red-far-red light perception that enable plants to monitor their local light environment. This sensing capacity is determined by a small multigene family (PHYA-PHYE), and the different phytochromes direct distinct processes during the plant life cycle. Two key characteristics of the phytochrome family are unresolved: where the photoreceptors are localized in the cell; and whether different phytochromes transduce their signals through similar or distinct pathways. A clue to the possible location of phyB came from analysis of the C-terminal sequence - there was evidence of weak homology to nuclear localization signals. To test the efficiency of the nuclear localization signals in transgenic Arabidopsis, the authors prepared a construct encoding the Cterminal domain and ghicurenidase (GUS). Cellular staining for GUS activity revealed that the fusion protein localized to the nucleus. However, the C-terminal domain lacks the chromophore that is required for phyB to operate as a photoreceptor and, as expected, light quality had no effect on the nuclear localization of the protein.

A study into the influence of light treatments on phyB localization was therefore .conducted on endogenous phyB. Nuclei were isolated from light-grown leaf tissue, and their purity assessed using microscopy and enzyme markers. Whole-cell extracts and nuclear fractions were then subjected to SDS-polyacrylamide gel electrophoresis and immunoblotting, using a monoclonal antibody to assess the distribution of endogenous phyB. In light-grown plants, nuclear phyB accounted for a significant proportion of the total cellular phyB, and this was confirmed by immunocytochemistry. Dark-adapted plants contained less phyB in the nucleus, and this process was accelerated by treatment with far-red light. This suggests that the partitioning of phyB between the cytosol and the nucleus is light dependent. This contrasts with the situation for phyA, because heteretrimeric G proteins, cyclic AMP and calcinm/calmodulin have all been implicated in the phyA signal transduction pathway. Thus, at least two members of the phytochrome gene family appear to operate via independent signalling pathways in response to light.

Wild relatives Jinhua, X., Grandillo, S., Ahn, S.N., McCouch, S.R., Tanksiey, S.D., Li, J. and Yuan, L. (1996) Genes from wild rice improve yield, Nature 384, 223-224 The wild relatives of modern crop plants are unremarkable for their yield, because it is this trait above all others that has been the primary target of selection. Nevertheless, preservatio n of the germplasm of these relatives has long been recognized as important - it is vital, for example, to maintain genes that could provide disease resistance or improved stress tolerance. However, recent correspondence in Nature suggests that a wild relative of rice, Oryza rufipogon - which has a typical yield ofjust 3.0 tonnes ha -1- can actually be used in crossing experiments with an elite modern cultivar to produce progeny that outstrip the yield of their top-performing parent. Jinhua et al. used a high-yielding first generation hybrid rice, V/64, for their experiments (typical yield 7.0 tonnes ha-l). After a series of crosses to allow the introgression of genes from O. rufipogon, a new rice variety

was created containing approximately 5% O. rufipogon genetic material. As expected, the vast majority of the lines created had a lower yield than V/64, but several lines did outperform it - by as much as 50% in some cases. Analysis using restriction-fragment length polymorphisms, microsatellite markers and quantitative trait locus mapping revealed that the increase in yield was associated with the insertion of O. rufipogon alleles into two regions, one on chromosome 1 and the other on chromosome 2. Both alleles exerted their effects by increasing the number of grains per plant, and the advantage over V/64 was estimated to exceed 1 tonne ha -1. Breeders are continually searching for new ways in which to increase yield, and so to feed the increasing world population. If the example presented by Jinhua et al. is typical, then wild relatives could soon become important new tools.

February 1997, Vol. 2, No, 2

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