BAK1和RGIS1参与RGFs-RGIs-PLTs信号通路调控根发育的分子机理

Root is an important vegetative organ， possessing multiple physiological functions including mechanical fixation, absorption of water and nutrients, and storage of various compounds. Root initiates from a group of specific cells named as stem cell niche in root tip. Previous studies indicated that multiple regulatory pathways are involved in the maintenance of stem cell niche. RGF1, a peptide hormone, plays a key role in the maintenance of stem cell niche. The receptors of RGF1, RGIs/RGFRs, were recently identified by three independent research groups including ourselves. RGIs belong to the single-pass transmembrane protein kinases named as receptor-like protein kinases (RLKs). Additional regulatory components are yet to be identified. BAK1 plays as a co-receptor in multiple RLK-mediated signaling pathways regulating plant growth and development. Our preliminary results indicated that BAK1 is also involved in the signal transduction of RGF1 in regulating root development. Using a forward genetic approach, we recently isolated two genetic suppressors of the quintuple mutant of RGIs, rgis1-1D and rgis2-1D. The encoding gene for rgis-1D, RGIS1, has been preliminarily determined. This proposal aims to further study the detailed molecular mechanisms of BAK1 and RGIS1 in regulating root development. We also propose to map the mutant gene of rgis2-1D and screen for other regulatory components in this signaling pathway. These studies will contribute to our better understanding the RGF1 mediated signal transduction pathway. The knowledge can also be used for future crop improvement via genetic engineering.

根是植物的重要营养器官，具有固着、吸收和储存等生理功能。根的生长源于根尖的干细胞微环境，干细胞微环境的维持涉及复杂的调控网络。多肽激素RGF1在干细胞微环境的维持过程中发挥重要功能，RGF1的受体RGIs/RGFRs已由本课题组等三家研究团队独立鉴定到，调控RGF1信号途径的其他元件亟待阐明。BAK1作为共受体参与多条信号途径，调控植物的生长发育。我们的初步结果表明BAK1参与RGF1的信号转导进而调控根发育；利用正向遗传学手段，我们还筛选到rgi1 rgi2 rgi3 rgi4 rgi5的两个遗传抑制子rgis1-1D和rgis2-1D，基本确定了rgis1-1D的突变基因。本项目旨在深入开展BAK1和RGIS1参与RGF1信号转导的分子机理研究，同时鉴定rgis2-1D的突变基因，筛选其它调控元件。深入解析RGF1的信号转导途径具有重要的理论意义，对今后的分子育种也具有重要的指导意义。

作为植物的重要营养器官，根承担着固着、吸收、疏导、合成以及贮藏等重要的生理功能。根的生长发育离不开根尖干细胞微环境的维持。RGFs是一类磺酸化的多肽，在根尖分生组织的发育中起着关键性的作用。拟南芥基因组编码11个RGFs成员。其中，RGF1、RGF2、RGF3在根尖表达并参与干细胞微环境的维持。RGFs被受体RGIs/RGFRs感知以后，能够维持下游的两个AP2类转录因子PLT1和PLT2的表达以及稳定PLT2的蛋白。尽管先前的研究表明，BAK1及其同源蛋白SERKs可能作为RGIs的共受体，详尽的遗传和生化等证据仍然缺失。这里，我们报道了SERKs的缺失突变体表现出根短以及对RGF1不敏感的表型。RGF1能够诱导RGIs与SERKs二聚化以及相互磷酸化。并且RGF1诱导下游的MAPK级联过程也是依赖RGIs和SERKs的。我们还分析了不同RGIs成员在根尖分生组织发育过程起着不同的作用。因此，我们通过完善的遗传和生化证据证明了SERKs作为RGIs的共受体，在RGF1介导的信号转导过程起着关键性的作用。. 我们发现MAPK级联过程能够介导RGF1的胞质信号传递。在RGF1的诱导下两个丝裂原活化蛋白激酶成员MKK4和MPK3能够与RGI1免疫共沉淀。遗传学和生物化学分析表明MKK4/MKK5以及MPK3/MPK6处于RGIs的下游进而调控根分生组织的发育。YDA作为MKK4/MKK5上游的MAPKKK在RGF1-RGIs信号通路中发挥功能。这些结果表明，YDA-MKK4/5-MPK3/6作为RGF1-RGIs的下游信号传导组分参与RGF1的信号转导。. 我们还分析了RGFs家族多肽在陆生植物中的起源。在24个陆上植物代表种中鉴定到203个RGFs编码基因。RGFs家族基因通过多次复制事件而扩增。不同物种中的RGFs-RGIs具有功能上的保守性。