Evolutionarily Conserved , T1SS, and Hydrogenase System in Rhizobia of and .

species are the main microsymbionts associated with the medicinal or sand-fixation plants and (AC) in temperate regions of China, while all the strains isolated from each of these plants could nodulate both of them. However, strain CCBAU01603 could nodulate AC plants and it's a high efficiency symbiotic and competitive strain with . Therefore, the common features shared by these symbiotic rhizobia in genera of and still remained undiscovered. In order to study the genomic background influencing the host preference of these AC symbiotic strains, the whole genomes of two ( CCBAU01550, CCBAU45272) and five representative strains ( CCBAU01583, CCBAU01570, CCBAU01502, CCBAU01399, and CCBAU01603) originally isolated from AC plants were sequenced, respectively. As results, type III secretion systems (T3SS) of AC rhizobia evolved in an irregular pattern, while an evolutionarily specific region including , T1SS, and a hydrogenase system was detected to be conserved in all these AC rhizobia. Moreover, was verified to be prevalently distributed in other AC rhizobia and was presumed as a factor affecting the nodule formation process. In conclusion, this research interpreted the multifactorial features of the AC rhizobia that may be associated with their host specificity at cross-nodulation group, including , T1SS as the possible main determinants; and , hydrogenase system, and T3SS as factors regulating the bacteroid formation or nitrogen fixation efficiency.