Investigation of Plant Genes Expressed During Symbiotic Nitrogen Fixation

Abstract

The development of the legume root nodule results from a complex interaction between Rhizobium and its host, requiring the co-ordinated expression of both bacterial and plant genes. To understand the molecular processes involved, an analysis of the genes of both partners is necessary. A great deal of progress has been made in identifying numerous Rhizobium genes (nif, nod, fix, etc.) involved in the symbiosis; relatively less progress has been made in identifying plant genes. In recent years, nodule specific plant proteins, nodulins, have been detected in soybean (1), pea (2), and alfalfa (3); but except for a few nodulins, little is known about their roles. Isolation and analysis of the nodulin genes will lead to a better understanding of the role of the plant genes and how they are regulated. To this end we have isolated and characterized five nodule specific cDNA clones from a soybean nodule cDNA gene bank (A). The clones have also been used to probe mRNA from nodules derived from the Frankia-alder symbiosis with the hope that some homology may exist between soybean and alder nodulins (B).