Enhancement technology of bacterial infection by rhizobitoxine

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We have investigated rhizobitoxine biosynthetic pathway and the function in Bradyrhizobium elkanii. In addition, we examined whether the ability to produce rhizobitoxine may improve rhizobial symbiosis and Agrobacterium-mediated transformation. DNA sequence and mutational analysis of rhizobitoxine biosynthetic genes revealed that at least rtxA and rtxC are requiered for rhizobitoxine biosynthesis in Bradyrhizobium elkanii. Application of ethylene precursor and inhibitors for ethylene biosynthesis and perception suggested that an ethylene-mediated signaling pathway is involved in the nodulation process even in the determinate nodulators including Lotus japonicus and Macroptilium atropurpureum. Rhizobitoxine competitively inhibited 1-aminocyclopropane-1-carboxylate synthase in ethylene biosynthetic pathway of host plants, and enhanced nodulation and competitiveness of B. elkanii on M. atropurpureum. Interestingly, Rhizobitoxine enhancement of competitive nodulation occurred at a late stage in the time-course of nodulation. We have been trying to confer the ability to produce rhizobitoxine of B. elkanii into other gram-negative bacteria by plasmids carrying rtxAC.