Regulation of Nodule Specific Genes

One of the unique developmental processes studied in plants is the induction and formation of nitrogen fixing root nodules on leguminous plants. Several plant genes encoding “nodulins” specifically involved in different stages of nodulation has been characterised (Listed in Delauney and Verma 1988). Early nodulin genes induced shortly after infection with the rhizobial microsymbiont respond to signal molecules excreted by the bacteria, while later nodulin genes like leghemoglobin responsible for oxygen transport in the mature nodule seem to require additional factors for induction (Govers et al. 1986/ Scheres et al. 1990). In an approach to study the regulatory circuits directing expression of nodulin genes we have used a Lotus corniculatus transformation regeneration system (Petit et al. 1987; Stougaard et al. 1987; Hansen et al. 1989) to define cis-acting regulatory DNA elements on both early and late nodulin promoters. In this communication results from analysis of the soybean leghemoglobin 1bc 3 gene promoter will be presented, together with attempts to characterise trans-acting protein factors linking the developmental status of the cell to regulatory events at the promoter.