MOLECULAR-GENETIC ANALYSIS OF SUBTERRANEAN CLOVER-MICROBE INTERACTIONS

Trifolium subterraneum (subterranean clover) is of considerable econom ic importance to the Australian rural industries as a pasture legume. In addition to its commercial value, it has a number of specific attri butes-such as small seed size, diploidy, self-fertilization, the abili ty to be transformed and small genome-which make it a prime target for the modern techniques of molecular genetics. We report genetic and ph ysiological factors that control the production and excretion of the l ipooligosaccharide molecules formed by Rhizobium leguminosarum by. tri folii in the formation of the symbiosis with subterranean clover. Thes e molecules, synthesized by the products of the nodulation (nod) genes , are a major determinant of nodule occupancy and the strain selection imposed by the host plant. In addition, we have investigated which pl ant genes and proteins are activated in subterranean clover when they are either physically wounded, infected with Rhizobium, or attacked by red-legged earth mites. To analyse these interactions more precisely, we have cloned plant genes involved in the phenylpropanoid pathway an d used their promoters to construct transgenic subterranean clover pla nts. Our studies provide an insight into the nature and consequences o f the chemical exchange between plants and invading microbes.