Opa22 is an outer membrane protein identified in Mesorhizobium huakuii 7653R in our previous work.To investigate its functions during symbiotic nitrogen fixation,a random genomic DNA library of M.huakuii 7653R based on the bacterial two-hybrid system was constructed.The candidate proteins interacting with Opa22 were screened from the library and twelve positive clones were obtained and analyzed.This study will provide both new insights on understanding Opa22 functions during symbiosis and technique platforms for the further researches on the protein-protein interaction network as well.