BR抑制SUBRI1小肽信号途径促进植物生长发育的机制

Brassinosteroids (BR) are a class of unique plant hydroxysteroids that play important roles in a wide range of plant physiological and developmental processes. At the cellular level, BR can regulate cell elongation, cell division and cell differentiation. Using a severely-dwarfed Arabidopsis BR receptor mutant, bri1-101, we performed a large-scale suppressor screen and identified a semi-dominant extragenic suppressor subri1-1 bir1-101. Genetic mapping coupled with whole genome sequencing revealed that SUBRI1 encode a putative peptide. Genetics and transcriptomics analysis imply that SUBRI1 signaling might inhibit cell elongation to repress plant growth. Interestingly, subri1 mutation cannot affect BR signaling, however, BRs negatively regulates the SUBRI1 transcript abundance in a BRI1-dependent manner. Taken together, our results suggest that BRs suppress the SUBRI1-mediated signaling pathway to promote plant growth. In this research, we will apply genetics, molecular biology and biochemical methods to reveal the function of SUBRI1 signaling pathway in cell elongation, and the mechanism of BR inhibition SUBRI1 signaling pathway. Moreover, our study will also provide significant insight into the mechanisms of BR signaling in promoting cell elongation to mediate plant growth and development.

油菜素内酯(BR)在植物生长发育诸多阶段发挥重要的作用。在细胞水平上，BR能够调控细胞伸长、细胞分裂以及细胞分化等过程。在本项目中，我们前期通过遗传筛选得到BR受体(BRI1)强表型突变体bri1-101的抑制子subri1-1 bri1-101，该抑制子中编码小肽SUBRI1的基因发生突变。遗传学、转录组学分析表明，SUBRI1可能通过抑制细胞伸长对植物生长发育产生抑制作用。进一步的实验发现，小肽SUBRI1并不参与BR信号的传导，但BR能够抑制SUBRI1表达而促进植物生长发育。因此，我们将采用遗传学、分子生物学和生物化学的方法，研究SUBRI1信号通路对细胞伸长的调节以及BR抑制SUBRI1表达的分子机制，为深入研究BR在促进植物生长发育中的作用提供参考。

油菜素甾醇 (BR) 在植物生长发育以及逆境适应等诸多阶段发挥重要作用。在细胞水平上，BR能够调控细胞伸长、细胞分裂以及细胞分化等过程。在本项目中，我们前期通过遗传筛选得到BR受体 (BRI1) 强表型突变体bri1-101的抑制子subri1-1 bri1-101，该抑制子中编码小肽SUBRI1的基因发生突变。对SUBRI1的生物学功能以及调控植物生长发育的机制进行研究，得到如下结果：(1) SUBRI1突变并不能改变bri1-101突变体对BR的响应，小肽SUBRI1不参与调控BR信号传导；(2) SUBRI1突变导致bri1-101细胞变大；SUBRI1过表达植株呈现植株矮小的表型；与SUBRI1缺失突变体相比较，SUBRI1过表达株系中许多参与细胞壁合成、修饰和重组等基因具有差异性表达。这些结果表明，SUBRI1通过抑制细胞伸长对植物生长发育产生抑制作用；(3) 未羟基化修饰脯氨酸和C端天冬酰胺缺失的SUBRI1小肽不能抑制下胚轴的伸长，表明，SUBRI1小肽的羟基化修饰以及天冬酰胺残基对SUBRI1功能发挥具有重要作用；(4) BL处理野生型植株明显抑制SUBRI1基因的表达，而BL处理BR不敏感突变体bri1-9等不能影响SUBRI1基因的表达，并且bri1-9突变体中SUBRI1的表达量明显增加，说明，SUBRI1的转录受BR信号调控。生物化学和分子生物学等研究结果显示，BR信号通路下游核心转录因子BZR1，通过直接与SUBRI1基因启动子区域的结合而抑制SUBRI1基因的转录；(5) SUBRI1能够激活下游MAPK级联途径；(6) SUBRI1的受体可能是SUBRI1R。以上结果揭示了小肽SUBRI1通过抑制植物细胞伸长调控植物生长发育的机制，同时阐述了BR信号通过调节抑制子SUBRI1的表达而促进植物生长发育的作用方式。进一步研究将深入挖掘SUBRI1小肽下游信号传导过程，以揭示植物细胞生长发育的调控机制以及BR调控植物生长发育的新机制。