Plasmids impact on rhizobia-legumes symbiosis in diverse environments

摘要: Rhizobia are a well-known group of soil bacteria that establish symbiotic relationship with leguminous plants, fix atmospheric nitrogen, and improve fertility. To fulfill multiple duties in soil, rhizobia elaborated large complex multipartite genome composed several replicons. The genetic material is divided among various replicons, way to cope with, satisfy the diverse functions rhizobia. In addition main chromosome, which carrying essential (core) genes required for sustaining cell life, genomes contain extra-chromosomal plasmids, nonessential (accessory) genes. Occasionally, some mega-plasmids, denoted as secondary chromosomes or chromids, carry Furthermore, specific accessory gene sequences (the chromosomal islands) incorporated chromosome species Bradyrhizobium Mesorhizobium genera. Plasmids variable sizes. All plasmids Rhizobium constitute about 30–50% genome. have characters such miscellaneous genes, independent replication system, self-transmissibility, instability. regulate cellular metabolic enable host survive habitats even under stress conditions. Symbiotic receiving increased attention because their significance nitrogen fixation process. They (nod, nif fix) non-symbiotic conjugally-transferred by aid non-symbiotic, self-transmissible hence, brings major changes interactions specificity Besides, cells harbor one more accessory, regulating functions, rhizosphere colonization, nodulation competitiveness. entire rhizobia-plasmid pool interacting harmony provides substantial abilities environments. above concepts extensively reviewed fairly discussed.