AAKANX PANCHAL - MSc Candidate Tackling the rhizobium competition problem by engineering exclusive compatibility between legumes and inoculant rhizobia Legume plants can benefit tremendously from their relationship with nitrogen-fixing soil bacteria called rhizobia. Within structures rhizobia induce along legume roots called nodules, rhizobia fix atmospheric dinitrogen into ammonia. High nitrogen-fixing rhizobium inoculants can provide legume crops with enough bioavailable nitrogen under ideal conditions to limit nitrogen fertilizer use and its negative environmental impacts. However, low nitrogen-fixing rhizobia native to the soil can outcompete high nitrogen-fixing rhizobia for nodule occupancy, reducing the benefit to the legumes and ultimately perpetuating dependence on nitrogen fertilizer. A potential solution to this "rhizobium competition problem" is engineering exclusive compatibility at the level of nodule occupancy between high nitrogen-fixing rhizobium inoculants and their associated legume crops. Nodule occupancy begins with rhizobia producing Nod factors specific to legume Nod factor receptors, where Nod factors and Nod factor receptors are like keys and locks. It is the ability of low nitrogen-fixing rhizobia native to the soil to produce the same Nod factors as high nitrogen-fixing rhizobium inoculants that allows low nitrogen-fixing rhizobia to nodulate the legume. Exclusive compatibility between the rhizobium inoculant and legume crop would involve inoculant rhizobia producing Nod factors that are unique in the target environment and legumes producing matching Nod factor receptors, such that low nitrogen-fixing rhizobia producing the original Nod factors should no longer be able to nodulate the legume. To test the feasibility of using this strategy, we have been working towards genetically engineering a model rhizobium-legume pair, Sinorhizobium meliloti and Medicago truncatula, to use Nod factors and Nod factor receptors from a different rhizobium-legume pair, Mesorhizobium japonicum and Lotus japonicus. In my seminar, I will present our progress in bringing the Lotus japonicus Nod factor receptor genes together into a single construct for their eventual expression in Medicago truncatula.
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