Symbiosis with Chickpea
As a typical species nodulating the chickpea root, ''M. mediterraneum'' forms a mutualistic symbiosis with the legume crop. The associations between ''M. mediterraneum'' and its legume hosts have been reported to be mediated by type IV secretion system (T4SS) genes such as ''traG'' and improved by the addition of the ''clpB'' chaperone gene. The invasion of legume by ''Mesorhizobium mediterraneum'' was also documented to involve production of hydrolytic enzymes such as xyloglucanase. Several isolates of ''M. mediterraneum'' enhanced the growth of chickpea by efficiently mobilizing phosphorus from insoluble phosphates. The species could help chickpea increase production and protein content even under a moderate water deficit. However, it has also been reported that nodulation by the species on chickpea was reduced by water deficiency. Dual-inoculation of ''Glomus mosseae'' and ''M. mediterraneum'' helped ''Lathyrus sativus'' resist sulfate salinity stress, while the growth of ''M.mediterraneum'' was also found to be intolerant of salt stress of 200 mM NaCl. ''M. mediterraneum'' helped chickpea resist osmotic stress by enhancing nodular peroxidase and ascorbate peroxidase activities. Besides chickpea, ''Mesorhizobium mediterraneum'' and/or closely related taxa have also been found to form symbiotic relationships with many other crops and plants, including wild liquorice (''Astragalus glycyphyllos''), lentil (''Lens culinaris'' Medik), the South African legume species of the genus ''Lessertia'', black locust (''Robinia pseudoacacia''), ''Lotus tenuis'', ''Caragana'', and ''Astragalus cicer.'' ''Mesorhizobium mediterraneum'', along with many other species, contributed to diverse rhizobia nodulating chickpea worldwide, such as Northeast China, India, the North-West Indo Gangetic Plains, Ethiopia, Iran, and Portugal. These findings contribute to valuable pools of isolates that hold promises for increasing chickpea production in these soil types.References
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