-Nodulating Rhizobia Lacking Nod Factor Synthesis Genes: Diversity and Evolution in Shandong Peninsula, China.

is a semiaquatic legume that forms both stem and root nodules with rhizobia. Some rhizobia (AIRs) have been reported to nodulate the host using a Nod factor-independent pathway and possess photosynthetic abilities. To investigate the diversity and community structure of AIRs in China, a total of 300 rhizobial isolates were acquired from the root and stem nodules of grown at 4 sites in Shandong Peninsula, China. Nineteen representative strains were selected according to their phylogeny. With further classification in comparison with reference strains, 10 genospecies were defined based on the 16S rRNA gene phylogeny and multilocus sequence analysis (MLSA) of housekeeping genes (HKGs) , , , , , and In addition, 6 genospecies were found only in China. No nodulation gene (, , , or ) was detected in the AIRs isolates by PCR amplification and Southern blotting. Phylogenetic analysis of and the photosynthesis-related gene revealed their common origins. All representative strains formed root nodules, but only 9 representative strains for 4 genospecies formed stem nodules on , indicating that the stem nodulation process of is limited to some strains. The nucleotide diversity and recombination events of the HKGs, as well as and genes, showed that mutation contributes more than recombination in evolution. The distribution of dominant AIR genospecies was mainly affected by available nitrogen, organic carbon, total nitrogen, and pH. Our study helps to characterize the diversity and evolution of AIRs. rhizobia (AIRs) can form both root and stem nodules via Nod factor-independent processes, which distinguishes them from other rhizobia. This study systematically uncovered the diversity and community composition of rhizobia distributed in eastern China. Our results reclassified all the rhizobia across the world and represent a useful contribution to evaluating the diversity and distribution of the symbiont. The presence of novel genospecies specifically distributed in China enriched the rhizobia resources and provided insight into the geographic distribution of rhizobia. The phylogenetic relationship between and of rhizobia across the world provides insight into the evolution of their nitrogen fixation and photosynthetic abilities.