Abstract
The root nodules of leguminous plants will be the most suitable model system to understand the mechanism of endosymbiosis. However, host plant molecules that induce bacteroid differentiation are still unknown. Morphology of bacteroids from Medicago truncatula and Lotus japonicus are quite different from each other. The differences may be attributed to the different strategy of the host plant to establish symbiosis. The NCR genes of M. truncatula, that encode several hundred of cysteine-rich and potential-antimicrobial peptide, are absolutely expressed in nodules and can be associated with bacteroid differentiation. We postulate that intracellular rhizobia in the nodules of M. truncatula are challenged with a battery of the NCR peptides that induce the terminal bacteroid differentiation. Testing this hypothesis relies on localizing the peptides in nodules and analyzing their in vitro activity on Sinorhizobium meliloti, the microsymbiont of M. truncatula, and their in planta activity in L. japonicus nodules.
