Functional Evolutionary genomics: Inferring the origin and function of the genes involved in nodulation symbiosis with nitrogen fixation

这些具有重要固氮作用的共生基因可能经历了不同于其他管家基因的特殊进化过程。利用豆科植物共生的背景信息，比较了各种细菌的基因组信息，推测了新的共生基因和这种共生关系的进化。我们研究了大规模的系统发育分析，并揭示了基因的进化起源。与普遍接受的α-变形菌来源的根瘤菌的情况相反，我们详尽的分析表明，根瘤菌与豆科植物的共生可能起源于β-变形菌家族。此外，我们还发现，有几个基因的共生功能目前还不知道的可能性是根瘤细菌的特征。我们通过基因的破坏证实了这些基因的共生功能。

There is a possibility that the symbiosis genes with an important role for the nodulation and nitrogen fixation passed through the special evolution that may be different from the other housekeeping genes. We compared the genomic information of various bacteria using the background information of symbiosis with legumes and inferred the new symbiotic nodulation genes and the evolution of this symbiosis. We examined large scale phylogenetic profiling and revealed the evolutionary origin of nodulation genes. Contrary to the widely accepted scenario of the alpha-proteobacterial origin of rhizobia, our exhaustive analysis showed that the nodulation symbiosis of rhizobia with legumes may have originated from beta-proteobacterial family. Furthermore, we found that there was a possibility that several genes which symbiosis function was not known so far are characteristic of root nodule bacteria. We confirm the symbiosis function of these genes by the gene destruction.