MAPK信号通路介导微生物多糖威兰胶调控本生烟草根系生长发育的分子机制

植物根际微生物作为根际生态系统的组成部分，对于植物的生长发育、抗病抗逆、提质增产发挥重要作用。课题组在根际土壤的探索中获得一株鞘氨醇单胞菌Y501，分离纯化其发酵液组分探索发现，主要次级代谢产物多糖—威兰胶，能够诱导本生烟草根系内源生长素水平升高，促进根系生长发育。进一步研究发现，经威兰胶处理的本生烟草根系中生长素合成途径关进酶基因NbTAA1和NbYUC1的表达水平受到MAPK信号通路成员NbMEK1和NbMEK2的调控，然而二者间的交互关系不甚清晰。为阐明MAPK信号转导通路对本生烟草根系局部生长素合成途径的调控，揭示威兰胶的促生作用机制，本项目将筛选并鉴定MAPK通路下游参与生长素合成途径关键酶基因调控的转录因子，理清其间上下游关系，从而构建威兰胶促生作用信号转导网络。本项目的实施不仅能够揭示以威兰胶为代表的微生物多糖促生作用模式，也对绿色农业和分子育种的发展具有重要理论和现实意义。

Rhizosphere microbiotas which are the interface between soil and plant roots play an important role in plant growth, grain production and tolerance to biotic and abiotic stress. In our previous study of soil microorganism, Sphingomonas sp. Y501 was isolated and identified, whose fermentation broth exhibited good plant growth- promoting properties. To investigate more information underlying the effect, the main components were extracted and purified. It showed that the extracellular polysaccharides (EPS) of Sphingomonas sp. Y501 - welan gum promoted the growth and development of Nicotiana benthamiana roots through improving the content of endogenous IAA. Further study showed that the expression of key molecules of auxin biosynthetic pathway, NbTAA1 and NbYUC1, were regulated by NbMEK1 and NbMEK2, the members of mitogen-activated protein kinase (MAPK) signaling pathway in welan-treated Nicotiana benthamiana roots. However, the regulatory mechanism remains unknown. In order to illustrate the mechanism of growth-promoting effect of welan gum on Nicotiana benthamiana roots, our study aims to identify the substrates of NbMEK1 and NbMEK2 which regulate the expression of NbTAA1 and NbYUC1 with a combination of molecular biological and genetic approaches, and then to construct the welan-mediated signaling transduction network. Our study will provide new insights into the mode of action of EPS-correlated growth-promoting effects as well as the theoretical and practical significance to the development of eco-agriculture and molecular breeding.