RLA1及其互作蛋白参与油菜素甾醇信号转导并调控水稻株型的细胞、遗传和分子机制研究

Leaf erectness is an important trait to determine rice plant architecture and grain yield, but the underlying cellular and molecular mechanisms that regulate leaf erectness development remain big mysteries. Through genetic screening for brassinosteroid-insensitive rice mutants in lanima inclination and map-based cloning, we identified RLA1 as a novel gene involved in the BR signaling pathway, and it can physically interact with the BR signaling components OsGSK2 and OsBZR1. In addition, by analysing the genes specifically expressed in the lamina joints, we found a X gene can be used as a tissue-specific molecualr marker of the lamina joint development. In this proposed study, we plan to investigate the cytological structure and gene regulatory networks in the leaf joint at different developmental stages. Using various modern biology approaches, we will investigate how RLA1 participates the BR signaling and what are the genetic, cellular and biochemical mechanisms of leaf joint development. This study will greatly enhance our understanding on the specific BR signaling pathway in rice and disclosure the cellular mechanism and genetic and biochemical network that RLA1 and it’s interactors regulate leaf joint development, which can provide the theoretical basis to create ideal plant architecture and increase grain yield in rice and other cereal crops.

叶直立性是与水稻产量密切相关的重要株型性状，但是调控叶直立性的细胞学机制及其遗传调控网络还很不清楚。我们通过筛选叶倾角对油菜素甾醇不敏感的突变体和图位克隆，发现RLA1是一个调控叶片直立性并参与油菜素甾醇信号转导的新基因，并且RLA1与水稻中的BR信号转导组分OsGSK2和OsBZR1互作。此外，通过分析叶枕特异的转录组，我们发现一个基因X可以作为叶枕发育的分子标记。本项目将在前期研究基础上，利用组织切片和叶不同发育时期的叶枕特异转录组，阐明叶枕发育的细胞学过程和基因表达调控网络；采用多种现代生物学的方法，研究RLA1及其互作基因参与BR信号转导并调控叶枕发育的遗传、细胞和生化机制。该研究将完善水稻中独特的BR信号转导通路；阐明RLA1及其互作基因控制水稻叶枕发育的细胞学机制及其遗传和生化网络；为塑造水稻的理想株型并提高产量提供理论依据。

本研究揭示了水稻叶枕从起始到发育成熟连续的细胞学结构动态变化和调控这一过程的基因表达调控网络；阐明了RLA1及其互作基因参与BR信号转导并调控叶枕发育的遗传、细胞和生化机制。我们通过正向遗传学的方法，以水稻的叶片直立性为性状，从水稻突变体库中筛选到表型为叶片直立，并且对外源BR不敏感的隐性突变体rla1。通过图位克隆和转基因互补验证，确定了RLA1就是引起突变体rla1表型的基因。遗传分析证明RLA1位于GSK2的下游，被OsBZR1功能依赖。序列分析表明RLA1是一个新转录因子，与已知的BR信号通路元件OsGSK2和OsBZR1在体外、体内都互作。通过遗传学、分子生物学和生物化学等方法，证明BR信号通过GSK2磷酸化RLA1来调控RLA1的蛋白稳定性，从而传递BR信号；而RLA1能够与OsBZR1互作，形成转录复合体，从而启动BR响应基因的转录；同时，也证明了RLA1能和水稻中另外一个已报道的GSK2的靶基因DLT互作，形成BZR1-RLA1-DLT的转录复合体。另一方面，我们以水稻日本晴第一完全叶为固定叶位，根据叶片的发育时期，将叶枕的发育分为5个时期，通过石蜡切片发现了叶枕发育的细胞学结构的动态变化，通过比较5个时期叶片和叶枕的转录组建立了调控叶枕动态发育的基因表达网络。因此，本研究不仅完善水稻中独特的BR信号转导通路，阐明RLA1及其互作基因控制水稻叶枕发育的细胞学机制及其遗传和生化网络，还为塑造水稻的理想株型并提高产量提供高通量的理论依据。