Nodulation of determinate and indeterminate legumes by Rhizobia expressing an auxin-synthesising chimeric operon

Leguminous plants can establish mutualistic symbiosis with soil bacteria called rhizobia; the interaction leads to the development of nitrogen-fixing root nodules. The formation of root nodules involves the activities of endogenous phytohormones, such as ethylene, cytokinin and auxin (IAA). It has been suggested that auxin play a different role in signaling for the initiation of determinate and indeterminate nodules. In order to study the effects of rhizobia-derived auxin on indeterminate and determinate nodule formation, we have engineered S. meliloti and R. leguminosarum by introducing an auxin-synthesising chimeric operon (rolAp-iaaMtms2) generating AUX strains, which allows to increase the amount of IAA produced by rhizobia within bacteroids in the nodules. Sinorhizobium meliloti induces indeterminate nodules in Medicago species, whilst Rhizobium leguminosarum is able to form determinate nodules in Phaseolus vulgaris.