Wide distribution range of rhizobial symbionts associated with pantropical sea-dispersed legumes
To understand the geographic distributions of rhizobia that associated with widely distributed wild legumes, 66 nodules obtained from 41 individuals including three sea-dispersed legumes (Vigna marina, Vigna luteola, and Canavalia rosea) distributed across the tropical and subtropical coastal regions of the world were studied. Partial sequences of 16S rRNA and nodC genes extracted from the nodules showed that only Bradyrhizobium and Sinorhizobium were associated with the pantropical legumes, and some of the symbiont strains were widely distributed over the Pacific. Horizontal gene transfer of nodulation genes were observed within the Bradyrhizobium and Sinorhizobium lineages. BLAST searches in GenBank also identified records of these strains from various legumes across the world, including crop species. However, one of the rhizobial strains was not found in GenBank, which implies the strain may have adapted to the littoral environment. Our results suggested that some rhizobia, which associate with the widespread sea-dispersed legume, distribute across a broad geographic range. By establishing symbiotic relationships with widely distributed rhizobia, the pantropical legumes may also be able to extend their range much further than other legume species.
KeywordsPantropical plants with sea-drifted seeds Rhizobia biogeography Sea dispersal
We thank Drs. Tetsuya Sado and R. Tapia-López for experiments Drs. Hidetoshi Kato, J. Torres García, D López, L. Martínez-García, Laura Giraldo, Ms. Adriana and Mr. Takashi Yamamoto for field sampling and Drs. Takeshi Asakawa and Yasuyuki Watano for their valuable comments. This work was supported by JSPS KAKENHI 15H05232 and 19370032 to TK, 26660057 to SA, and MEXT TOBITATE! Young Ambassador Program 2014 to MB. Sample collection was supported by KAKENHI 18370038 to Hidetoshi Kato (Tokyo Metropolitan University) and Fujiwara Natural History Foundation to KT.
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