Characterization of the Nodulation Functions in Bradyrhizobium sp. WM9 (Lupinus)

Abstract

Bradyrhizobium sp. WM9 nodulates lupines (Lupinus), broom (Sarothamnus), laburnum (Cytisus), seradella (Ornithopus), and bird’s foot trefoil (Lotus). Host range is determined by the lipochitooligosaccharides (LCOs), whose structures depend upon the nod genes present in rhizobium genome. The sequencing data revealed similarity of the nod cluster in WM9 to the nod regions in other bradyrhizobia. The most conserved part comprises regulatory, common nod and nodSUIJ genes. The only difference is related with the ORF1 sequence located upstream nodA which codes for a product similar to „hypothetical 126 protein“ from B. japonicum. More differences were found close to nodZ gene: the first concerns a nolL homologue present downstream this gene. nolL which has been identified in other Rhizobium species being involved in acetylation of fucose, a modification which in this case may be crucial in determination of the host range. Other difference relates to the genes located immediately upstream nodZ. In B. japonicum USDA110 this region carries four ORFs known as nolM, nolN, nolO and ORPA. WM9 lacks homology to nolM and ORFA, while nolN and nolO form a single gene. nolO in WM9 codes for a protein of 682 amino acids versus 338 in USDA110. The length of nolO in WM9 resembles nolO from R. sp. NGR234, which also contains nolN homologue in its N-terminal end. Moreover, C-terminal ends of nolO in WM9 and NGR234 are similar in this part which in USDA110 corresponds to ORFA.