Gene Is Conserved across spp. Able to Nodulate the Same Host Plant and Expressed in Response to Root Exudates.

Evidences for an involvement of the bacterial type IV secretion system (T4SS) in the symbiotic relationship between rhizobia and legumes have been pointed out by several recent studies. However, information regarding this secretion system in is still very scarce. The aim of the present study was to investigate the phylogeny and expression of the gene, which encodes a substrate receptor of the T4SS. In addition, the occurrence and genomic context of this and other T4SS genes, namely, genes from and complexes, were also analyzed in order to unveil the structural and functional organization of T4SS in mesorhizobia. The location of the T4SS genes in the symbiotic region of the analyzed rhizobial genomes, along with the phylogeny, suggests that T4SS genes could be horizontally transferred together with the symbiosis genes. Regarding the T4SS structural organization in , the genes were absent in all chickpea ( L.) microsymbionts and in the symbiont MAFF303099. Interestingly, the presence of genes belonging to another secretion system (T3SS) was restricted to these strains lacking the genes. The gene expression was detected in Ca36 and LMS-1 strains when exposed to chickpea root exudates and also in the early nodules formed by Ca36, but not in older nodules. This study contributes to a better understanding of the importance of T4SS in mutualistic symbiotic bacteria.