Photobiology and Photosynthesis Research Unit, National Institute of Agrobiological Sciences, Tsukuba, Ibaraki, 305-8602 Japan.
Plant Cell Physiol. 2012 Sep;53(9):1570-82. doi: 10.1093/pcp/pcs097. Epub 2012 Jul 3.
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.
与双子叶植物中赤霉素代谢的光调控有大量知识相比，单子叶植物中的这方面知识还很不清楚。在这项研究中，我们发现蓝光信号触发水稻幼苗中活性赤霉素含量的降低，同时抑制两个赤霉素 20-氧化酶基因（OsGA20ox2 和 OsGA20ox4）和四个赤霉素 2-氧化酶基因（OsGA2ox4-OsGA2ox7）的表达。为了进一步研究这些基因的调控，我们通过从 Tos17 突变体群体中进行反向遗传学筛选和基于 RNA 干扰技术构建敲低系，建立了一系列隐花色素缺陷系。通过使用这些系和光敏色素突变体，我们阐明了隐花色素 1（cry1），由水稻植物中的两个种组成（cry1a 和 cry1b），对于 GA2ox 基因的强烈诱导是必不可少的。另一方面，GA20ox 基因的抑制是由光敏色素介导的。此外，我们发现光敏色素也介导了光下 GA3ox2 基因的抑制。这些结果表明，在水稻幼苗中，光敏色素介导赤霉素生物合成能力的抑制，而 cry1 介导赤霉素失活能力的诱导。cry1 的作用在活性赤霉素含量的降低中表现为优势，但在水稻幼苗中，这些独立作用的累积效应降低了光下活性赤霉素的含量。这种不同类型的光受体独立但协同调节活性赤霉素含量的途径设计在双子叶植物研究中是独特的。这种冗余性应该为水稻植物的响应提供鲁棒性。
