GMN56, A NOVEL NODULE-SPECIFIC CDNA FROM SOYBEAN ROOT-NODULES ENCODES A PROTEIN HOMOLOGOUS TO ISOPROPYLMALATE SYNTHASE AND HOMOCITRATE SYNTHASE

We have isolated a novel nodule-specific cDNA clone, GmN56, from soybean root nodules, The expression of GmN56 was induced almost concomitantly with the onset of nitrogen fixation, together with leghemoglobin and other late nodulin genes, In situ hybridization studies demonstrated the localization of GmN56 mRNA in the bacterial infected cells of mature nodules, The predicted amino acid sequence of the GmN56 protein exhibits significant homology to those of LeuA (isopropylmalate synthase) of several microorganisms and NifV (putative homocitrate synthase) of nitrogen-fixing bacteria, suggesting that GmN56 encodes an enzyme catalyzing a reaction involving acetyl-CoA and alpha-keto acid as substrates.