title: Cryptochrome and phytochrome cooperatively but independently reduce active gibberellin content in rice seedlings under light irradiation.
abstract: In contrast to a wealth of knowledge about the photoregulation of gibberellin metabolism in dicots, that in monocots remains largely unclear. In this study, we found that a blue light signal triggers reduction of active gibberellin content in rice seedlings with simultaneous repression of two gibberellin 20-oxidase genes (OsGA20ox2 and OsGA20ox4) and acute induction of four gibberellin 2-oxidase genes (OsGA2ox4-OsGA2ox7). For further examination of the regulation of these genes, we established a series of cryptochrome-deficient lines through reverse genetic screening from a Tos17 mutant population and construction of knockdown lines based on an RNA interference technique. By using these lines and phytochrome mutants, we elucidated that cryptochrome 1 (cry1), consisting of two species in rice plants (cry1a and cry1b), is indispensable for robust induction of the GA2ox genes. On the other hand, repression of the GA20ox genes is mediated by phytochromes. In addition, we found that the phytochromes also mediate the repression of a gibberellin 3-oxidase gene (OsGA3ox2) in the light. These results imply that, in rice seedlings, phytochromes mediate the repression of gibberellin biosynthesis capacity, while cry1 mediates the induction of gibberellin inactivation capacity. The cry1 action was demonstrated to be dominant in the reduction of active gibberellin content, but, in rice seedlings, the cumulative effects of these independent actions reduced active gibberellin content in the light. This pathway design in which different types of photoreceptors independently but cooperatively regulate active gibberellin content is unique from the viewpoint of dicot research. This redundancy should provide robustness to the response in rice plants.
authors: Photobiology and Photosynthesis Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602 Japan. fumih@affrc.go.jp
authors: Fumiaki
authors: F
authors: Hirose
authors: Noritoshi
authors: N
authors: Inagaki
authors: Atsushi
authors: A
authors: Hanada
authors: Shinjiro
authors: S
authors: Yamaguchi
authors: Yuji
authors: Y
authors: Kamiya
authors: Akio
authors: A
authors: Miyao
authors: Hirohiko
authors: H
authors: Hirochika
authors: Makoto
authors: M
authors: Takano
mesh_terms: D056931:Cryptochromes / Q000378:metabolism*; D003624:Darkness; D018506:Gene Expression Regulation, Plant / Q000528:radiation effects; D055785:Gene Knockdown Techniques; D017343:Genes, Plant / Q000235:genetics; D005875:Gibberellins / Q000096:biosynthesis / Q000378:metabolism* / Q000494:pharmacology; D008027:Light; D008954:Models, Biological; D009154:Mutation / Q000235:genetics; D012275:Oryza / Q000235:genetics / Q000378:metabolism* / Q000528:radiation effects*; D010834:Phytochrome / Q000378:metabolism*; D018515:Plant Leaves / Q000033:anatomy & histology / Q000528:radiation effects; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D036226:Seedlings / Q000378:metabolism* / Q000528:radiation effects; D015398:Signal Transduction / Q000235:genetics / Q000528:radiation effects; D014158:Transcription, Genetic / Q000528:radiation effects
chemical_list: D056931:Cryptochromes; D005875:Gibberellins; D010940:Plant Proteins; D010834:Phytochrome