XYLEM COLONIZATION OF THE LEGUME SESBANIA-ROSTRATA BY AZORHIZOBIUM-CAULINODANS

A novel pathway of invasion of the legume Sesbania rostrata by Azorhiz obium caulinodans is described that involves colonization of the root xylem, possibly following entry into the natural fissures created duri ng emergence of lateral roots. Azorhizobia were detected microscopical ly, and their presence confirmed by the expression of a lacZ reporter gene. We have shown that rhizobial Nod factors are not required for ei ther xylem colonization or for crack-entry of lateral roots. We discus s the extent to which this discovery of xylem colonization by azorhizo bia is likely to improve our understanding of both symbiosis and of pa thogenicity in plant-bacterial interactions.