MAPK级联信号在植物生长发育过程中对生长素合成的调节

Auxin plays critical roles in plant growth and development. Recent studies revealed that, in additional to auxin polar transport, localized auxin biosynthesis is also important to auxin-regulated processes in plants. There are several possible auxin biosynthetic pathways, including the recently confirmed TAA-YUC pathway. However, we know very little about the signaling pathway(s) that regulate auxin biosynthesis. ..Plant receptor-like protein kinases (RLKs) and their peptide ligands play key roles in coordinating the cell proliferation and differentiation in plant morphogenesis. Mitogen-activated protein kinase (MAPK) cascades are key signaling modules downstream of receptors/sensors in transducing the extracellular stimuli to cellular responses. Our recent studies revealed that MPK3 and MPK6, two Arabidopsis MAPKs, are critical to a variety of plant growth and developmental processes including the first asymmetric cell division of zygotes, embryogenesis, stomatal differentiation, abscission, and localized cell division downstream of RLKs. Loss-of-function (LOF) of MPK3 and MPK6 also leads to several auxin related phenotypes. Together with the increase in auxin levels and DR5 reporter activity in the gain-of-function (GOF) MPK3/MPK6 transgenic plants, we speculate that MPK3/MPK6 cascade is involved in regulating auxin biosynthesis...In this project, we are going to study the mechanism underlying the function of MPK3/MPK6 cascade in signaling the localized auxin biosynthesis, which might play a key role in regulating localized cell division and morphogenesis downstream of ERECTA and its ligand EPFL4/EPFL6. Auxin levels and activities will be monitored using DR5 reporters and direct auxin quantification. In combination with genetic analyses using mutants of auxin biosynthetic genes, we are going to determine whether one or both potential auxin biosynthetic pathways (TAA-YUC and CYP79B2/B3) are regulated by MPK3/MPK6 cascade. These analyses will be linked to phenotypic alterations in GOF and LOF mutants/transgenics of MPK3/MPK6 cascade, its upstream ERECTA receptor and EPFL4/EPFL6 ligands. Furthermore, we are going to identify the substrate(s) of MPK3/MPK6 in this pathway using a combination of genetic and phosphoproteomic approaches. ..Auxin is a major growth-promoting hormone and plays important roles in almost all aspects of plant life cycle. The identification of novel signaling pathway that regulates auxin biosynthesis and understanding their function in localized cell division will provide us new venues to engineer crops with improved morphology/architecture and enhanced yield.

生长素在植物的生长发育中起着重要作用。近年来对生长素的合成途径研究取得了重要进展，生长素的区域性合成在调控植物生长发育中的关键作用逐步被认识，但关于生长素合成的调控信号通路知之甚少。MAPK级联信号是植物类受体蛋白激酶下游信号传导的核心组成部分。我们前期研究发现拟南芥MPK3/MPK6在调控区域性细胞分裂中起关键作用，并参与调控多个植物生长发育过程，MPK3和MPK6功能缺失能导致一系列与生长素相关的生长发育缺陷表型。本项目拟对MPK3/MPK6级联信号途径调控生长素的合成进行系统研究，同时鉴定其下游调控生长素合成基因的转录因子，旨在阐明MAPK调控的生长素合成途径及分子机制，揭示一条从类受体蛋白激酶与其多肽配体互作，激活MAPK级联信号，调控生长素合成基因表达，改变局部生长素浓度，最终影响植物细胞分裂及形态建成的完整通路及分子机制，为农作物生长发育、株型改造及分子育种提供重大理论依据。

本项目围绕MPK3/MPK6级联信号、区域性细胞分裂与分化、生长素的分布和活性三个关键点研究植物区域性细胞分裂及形态建成的信号通路及分子机制。之前我们发现MPK3/MPK6级联信号调控多个与生长素密切相关的发育过程，在此基础上，我们发现MKK4/MKK5-MPK3/MPK6级联信号在调控植物侧根原基的发生和侧根的形成方面也起着十分重要的作用。该信号通路的缺失使植物侧根数目明显减少，并伴随生长素在侧根原基中的分布及其下游响应发生紊乱。进一步研究发现MKK4/MKK5-MPK3/MPK6级联可能在IDA (配体)-HAE/HSL2 (激酶受体)下游通过调控生长素响应以及细胞壁重建从而调控了侧根的发生及形成。该研究结果将对深入理解植物侧根的发生及形成机制有重要意义。此外我们还通过总结自己课题组及其他课题组多年的工作，在Trends in Plant Science杂志阐述了MPK3/MPK6调控植物生长发育的分子机制，深入探讨了同一MAPK级联信号控制多个生长发育过程的信号特异性机制，对国内外植物生长发育研究领域的科研人员具有重要的参考价值。在该项目支持下，共发表SCI论文4篇，专著章节1篇。