Cloning the Genes That Allow a Rhizobium Leguminosarum Strain to Nodulate Afghan Peas

Unlike most strains of R. leguminosarum, the Turkish strain TOM is able to nodulate pea cv Afghanistan, in addition to commercial varieties of peas(Winamo, Lie, 1979). The extended host range of TOM is a property of its symbiotic plasmid, pRL5JI (Brewin et al. 1980). A gene bank was constructed in the cosmid vector pLAFR1. Following transfer to a strain of R. leguminosarum that had been cured of its symbiotic plasmid, several clones were isolated that were each able to nodulate both cv. Afghanistan and commercial pea varieties. One of these clones, pIJ1095, was subjected to mutagenesis with transposon Tn5. From one hundred Tn5 insertions screened, 11 affected the nodulation ability and all these were mapped to a region of only 6kb. The mutants fell into three classes on the basis of their map positions and phenotypes (table 1).