042BM noeA was obtained by PCR. It is identical to that of S. meliloti 1021 at 99% level, and similarity of their NoeA is 97%. In addition, it was found that this protein shares significant homology with the SAM-dependent methyltransferase of Mesorhizobium sp. BNC1 (32% similarity), and the similarity of its 303-362 region to the 160- 220 region of Ll11 methyltransferases of E. coli (PrmA) is 41%. Compared to 042BM, the noeA deletion mutant 042BMA-Km showed different degrees of increase in number of nodule, fresh weight of nodule and plant top dry weight on alfalfa cultivars of Putong Zihua, Baoding, Ningxia, Baifa and Aohan, but decrease on Milu. However, this mutant has no significant change in ability to nodulate cultivars of Huanghou and Zahua. Hence, noeA is involved in alfalfa cultivar-specific nodulation.