不同根瘤菌与苦参的混杂性共生机制研究

豆科植物苦参可以与明显不同的根瘤菌建立起共生固氮关系，相对于专一性共生来说，可以称之为混杂性共生关系。在该共生关系中，系统发育地位不同、共生基因类型差异很大、原初的豆科宿主又不属于同一族群、不能在对方宿主上交叉结瘤的根瘤菌，为什么却都可与苦参共生？这些根瘤菌结瘤基因表达如何?所产生的结瘤因子结构有何特点？不能与苦参结瘤的根瘤菌，基因突变后却能结瘤了，为什么？针对这些问题，本项目在前期研究的基础上，拟开展以下工作：1)共同和专一性结瘤基因的删除、回补和互换，以检查苦参对不同根瘤菌结瘤基因的要求；2）受苦参分泌物——类黄酮和苦参碱诱导下的不同根瘤菌的结瘤基因表达情况，结瘤因子结构比较，以确定不同的根瘤菌所产生的结瘤因子结构上是否有共性；3）对被突变的基因进行功能鉴定，研究其改变结瘤范围，调控固氮作用和类菌体发育的机制。通过上述研究，系统阐明苦参与不同根瘤菌建立混杂性共生关系的分子机制。

Relative to the specific symbiosis, the legume Sophora flavescens could establish symbiosis with obviously different rhizobia, and this relationship could be called as promiscuous symbiosis. In this system, why these different rhizobia whose differences on phylogeny, symbiotic genes, original host plants and cross nodulation, could establish symbiosis with Sophora flavescens? How about the expression of the nodulation genes? How is the structure of the Nod factor? Why the gene mutation could lead to change rhizobial host range? Based on the previous results and to answer these questions raised above, the current project will focus on the following researches: 1) deletion, complementation and exchange of the common and specific symbiotic genes to check the requirement for these genes in the nodulation with Sophora flavescens; 2) detection on the expression of nodulation genes induced by root secreta of Sophora flavescens including flavonoid and matrine, comparison on the structure of Nod factor to determine whether there are some common structures of the Nod factor produced by different rhizobia; 3) identification of mutated genes and exploration on the mechanism these genes participating in changing rhizobial host range and regulating the nitrogen fixation and development of bacteroid. By doing these studies, the aim of the project is to explain systematically the molecular mechanism of establishing promiscuous symbiosis between Sophora flavescens and different rhizobia.