项目组前期研究发现田菁根瘤菌共生岛基因能跨属向其它根瘤菌发生水平转移，并使后者获得在田菁上结茎瘤的能力，生物信息学分析发现该共生岛仅具有结瘤相关基因（nod），这在根瘤菌共生固氮基因组成上是非常独特的。本项目在前期工作基础上结合目前根瘤菌分子进化的新进展，从两方面开展研究，首先通过聚类分析等手段确定该共生岛不同功能基因的来源；其次将基因水平转移和实验室分子进化的方法相结合，对该共生岛基因向自生固氮菌水平转移进行研究，以获得新的具有结瘤、固氮能力的根瘤菌，筛选影响受体细菌接受共生岛水平转移的关键基因，研究这些基因在共生岛水平转移中的生理生化功能，探索宿主在根瘤菌分子进化过程中的作用，阐明根瘤菌进化的潜在分子机制，为扩大根瘤菌的种质资源，实现生物固氮在农业生产中更广泛地应用提供理论基础。

Horizontal gene transfer (HGT) of genomic islands is a driving force of bacterial evolution.we investigated the HGT of a symbiosis island in Azorhizobium caulinodans (ICEAc), harboring gene clusters involved in forming nitrogen-fixing nodules on Sesbania rostrata.We found that the ICEAc could conjugally transfer into some other rhizobia, allowing these strains to expand their host-range specificity. There are only nod genes in ICEAc that is different with its normal location in other rhizobia. In this study, we will study where did the ICEAc come from by analyse differnet fuctional genes in the island. Then we will cuse HGT couple with experimental evolution in order to introduce ICEAc into non-rhizobium strains. After selected by host, we want to get the new conjugants which may form nodlue on Sesbania rostrata. This work may demonstrate the key genes in non-rhizobium cells which affect gene transfer and the function of host in rhizobium evolution. It also may broaden the resources and the application of rhizobia in agriculture.