Rhizobia Genome: Diversity, Comparation, Evolution and Function

The rhizobium–plant symbiosis is a primary source of fixed nitrogen (ammonia) in the biosphere. Based on the genomic findings, several potential genes involved in symbiotic characteristics, such as nod, noe, and nol genes, play a role in nodulation, and nif and fix genes are responsible for nitrogen fixation in plant hosts. Legume plants are uniquely able to establish symbiosis with nitrogen-fixing bacteria. Rhizobia are alpha-proteobacteria commonly found in soil and the root nodules of legumes. The bacteria belonging to the genera Rhizobium, Bradyrhizobium, Allorhizobium, Sinorhizobium, and Mesorhizobium are referred to as rhizobia. For decades, research on rhizobia has benefited from using leading techniques from a comprehensive set of fields, including population genetics, molecular genetics, genomics, and systems biology. Numerous research strategies have been employed in studying rhizobia and the unique knowledge gained from these various tools, focusing on genome- and systemic-level approaches. This chapter describes the basic properties of rhizobia genomes, including their structure and the symbiotic genes that support nodulation and nitrogen fixation. Furthermore, this chapter reviews some genomic tools for the investigation of predictively molecular mechanisms involved in bacteriahost interaction (symbiotic and other interactions) and some findings about their comparative genome sequences and gene functions.