油菜素甾醇和细胞分裂素互作调控拟南芥胚珠原基发生的机制研究

In Arabidopsis，ovule is the precursor of seed. Ovule development and ovule number influence seed quantity and quality directly. Ovule primordia initiation is the basis of ovule development and ovule number. Investigating the mechanism of ovule primordia (protrusion) initiation has both scientific significance and potential application. It was reported that phytohormones, such as auxin, cytokinin (CK), and ethylene, function in ovule development and ovule number regulation. Our previous results showed that brassinosteroids (BR) also influenced ovule development and quantity regulation. BR affected ovule early development, ovule number, and seed set through regulating ovule early development related genes expression by BZR1. Also BR played key roles before ovule development; and during the processes of placenta formation, ovule identity, and ovule primordia initiation. In these process, the components of CK metabolism and signal transduction pathway were regulated by BR signaling. Base on previous research, this project will investigate the crosstalk of BR and CK functions in Arabidopsis ovule primordia initiation; identify joint-point genes; and analysis regulatory mechanism by using strategies of genetics and molecular biology, and so on. This work would be much helpful to illustrate the mechanism that how BR and CK crosstalk to regulate ovule primordia initiation, and give clues to enhance seed quantity and yield of similar crops.

拟南芥胚珠是种子的前身，胚珠发育和数量直接影响种子质量和数量。胚珠原基发生是胚珠发育和数量决定的基础，研究胚珠原基发生的调控机制具有重要科学意义和潜在应用价值。文献已报道植物激素生长素、细胞分裂素（CK）、乙烯等调控胚珠发育和数量。申请人前期研究成果表明植物激素油菜素甾醇（BR）也调控胚珠发育和数量，BR通过BZR1转录因子调控胚珠发育早期相关基因表达从而正调控胚珠发育和数量以及单果实的种子数，进一步研究发现BR在胚珠发育前、即胎座形成、胚珠原基特征决定和胚珠原基发生过程中已发挥作用，CK代谢和信号通路相关组分在胚珠原基发生过程中受到BR信号调控。本项目基于前期研究基础，通过遗传学和分子生物学等策略，系统研究BR和CK互作调控胚珠原基发生的信号网络，鉴定关键调控因子，解析相关调控机制，既有助于阐明BR和CK互作调控胚珠原基发生的机制，又为与拟南芥相近的农作物种子数量和产量提高提供新线索。

胚珠是种子的前体，胚珠原基发生决定了胚珠数量的最大可能性，并很大程度上影响了单果实种子数量，研究胚珠原基发生过程及其调控机制具有重要的科学意义和潜在的应用价值。出于材料有限和技术困难等原因，目前对胚珠原基发生的调控机制研究极少，申请人前期研究成果表明植物激素油菜素甾醇（BR）参与胚珠早期发育和数量调控并影响单果实种子数。本项目中申请人研究了胚珠原基起始的详细过程及其调控机制，发现同一胎座上的胚珠原基不同时起始，第一批胚珠在胎座中先凸起，随后胎座伸长，胚珠原基间距离增大，之后在第一批胚珠间的边界中再起始第二批胚珠。待两次起始过程完成后、两批胚珠的大小和形状接近一致时，两批胚珠几乎同时开始大孢子母细胞决定以及珠被分化等发育过程，但胚珠原基发生的异步性造成的胚珠发育时期的差异会保持到胚珠（及内含的雌配子体）发育成熟。该成果解释了多年前发现的同一雌蕊中存在两个相邻发育时期雌配子体的原因，暗示胚珠发生不同步而生长发育速度相似。生长素输出载体PIN1极性定位和生长素信号响应高峰的动态变化决定了胚珠原基的异步起始，我们构建了计算机模型来模拟这一过程。BR通过提高生长素信号促进胚珠起始，还可与细胞分裂素（CK）通过各自信号通路中的重要转录因子直接互作、更有效的提高CK信号下游胚珠原基发生促进因子STK等的转录水平，进而更有效的促进胚珠原基发生。BR和CK互相激活对方的信号，同时提高BR和CK信号可更有效提高胚珠数；但BR信号高可回复CK信号低的表型，而CK信号高则不能回复BR信号低的表型，说明BR促进胚珠原基发生部分经由CK信号、BR还可经由其他途径促进胚珠原基发生。本项目还建立了研究激素调控胚珠发生和发育的体外处理系统，并通过详细的转录组分析筛选出一批调控胚珠发生和发育的新基因，为进一步研究胚珠原基发生的调控机制奠定了基础，也为提高与拟南芥相近的十字花科和豆科农作物的种子数量提供了新线索。