IBN-9630189 de Bruin and Szczyglowski The formation of nitrogen fixing nodules on legume plants represents an unusual example of externally induced organogenesis under the influence of two different organisms, namely the plant host and symbiotic bacteria. This symbiotic process results in the creation of the appropriate microenvironment necessary to support the fixation of nitrogen by the prokaryotic symbiont and the assimilation of nitrogen by the plant host. Although the genetic components involved in nodule induction have been relatively well studies in the bacterial symbiont, a lot remains to be learned about the plant's contribution to the process. Preliminary genetic data have suggested a distinct connection between nodule morphogenesis and other plant developmental processes. The specific aim of this proposal is to test the hypothesis that common regulatory elements are involved in both lateral root formation and nodule organogenesis in the model legume Lotus japonicus, which is particularly amenable to combined genetic, physiological and molecular analyses. The L. japonicus har-1 mutant we have isolated, displays a drastically altered root morphology, as well as aberrant nodulation properties, and serves as the experimental basis of this proposal. By characterizing this mutant and the corresponding gene(s), we hope to learn more about the genetic determinants responsible for nodulation. In the very long run, this information may contribute towards the knowledge base required to extend the nodulation process to presently non-nodulated crop plants, such as the cereals.
