Contribution of Mobile Group II Introns to Sinorhizobium meliloti Genome Evolution

Mobile group II introns are ribozymes and retroelements that probably originate from bacteria. Sinorhizobium meliloti, the nitrogen-fixing endosymbiont of legumes of genus Medicago, harbors a large number of these retroelements. One of these elements, RmInt1, has been particularly successful at colonizing this multipartite genome. Many studies have improved our understanding of RmInt1 and phylogenetically related group II introns, their mobility mechanisms, spread and dynamics within S. meliloti and closely related species. Although RmInt1 conserves the ancient retroelement behavior, its evolutionary history suggests that this group II intron has played a role in the short- and long-term evolution of the S. meliloti genome. We will discuss its proposed role in genome evolution by controlling the spread and coexistence of potentially harmful mobile genetic elements, by ectopic transposition to different genetic loci as a source of early genomic variation and by generating sequence variation after a very slow degradation process, through intron remnants that may have continued to evolve, contributing to bacterial speciation.