Abstract
Systematic gene disruption experiments in Mesorhizobium loti MAFF303099 using ordered cosmid library were carried out to detect unidentified genes involved in symbiosis. One of the created mutants, DM002S, that lacked a 22-kbp chromosomal region showed non-nodulation phenotype on Lotus japonicus B-129. This mutant retained early symbiotic events such as root hair deformation, root hair curing and infection thread, suggesting that it has impairment in subsequent infection process. DM002S did not grow in minimal medium without supplementation of yeast extract or adenine. Among the deleted 22-kbp chromosomal region, only a 3-kbp fragment fully complemented both adenine auxotrophy and symbiotic defect. The 3-kbp region contains homologue of purB gene which encodes an adenylsuccinate lyase (EC 4.3.2.2) in the purine biosynthesis pathway. These results suggest that metabolic flow through purine biosynthesis or intermediate in the pathway is essential in early symbiotic interactions between M. loti and L. japonicus.
