Involvement of Rhizobium Bacteria in Regulation of the Plant L-Asparaginase Gene during Legume Nodule Development

Concomitant with the decrease in L-asparaginase activity and transcript levels seen in nitrogen-fixing leguminous nodules, the appearance of a trans-acting protein interacting with a specific sequence of the L-asparaginase promoter has been observed (Vincze et al. 1994). The functioning of this repressor binding site sequence in vivo was demonstrated in transgenic Lotus corniculatus plants. Gel retardation experiments and DNAsel footprint using bacterial protein extracts and protein extracts from developing nodules suggested a bacterial origin for the repressor binding protein. Our efforts to clone the repressor coding gene in E. coli background have been unsuccessful. This could be explained by (a) the clone not being present in the library; or (b) its promoter not being functional in E. coli; or (c) a requirement for the protein to be specifically phosphorylated, and this capacity not being present in the E. coli background used for this experiment.