Promoters of the soybean seed lectin homologues Le2 and Le3 regulate gene expression in vegetative tissues in Arabidopsis

Soybean seed lectin, Le1, is specifically expressed in seeds of soybean, Glycine max (L.) Merr., due to its promoter. Two genes, Le2 and Le3, homologues of Le1, were previously identified by computational analysis as possibly expressed in other parts of soybean. We cloned the promoters from these novel genes, and show that they drive differential reporter gene expression in transgenic Arabidopsis thaliana. A total of 1.3 kb was isolated from each of the Le2 and Le3 5′ promoter regions and fused with the gusA (GUS) reporter gene. A previously cloned Le1 5′ promoter was used as a seed-specific control and the constructs were introduced into Arabidopsis. A series of developing transgenic Arabidopsis seedlings were assayed for GUS over 15 days. GUS expression in transformed Arabidopsis plants reveals that GUS driven by the Le3 promoter is found predominantly in vegetative tissues including root, whereas GUS driven by the Le2 promoter shows low expression in all tissues examined, excluding roots. The Le1 and Le3 promoters lead to complementary expression profiles: as the effect of the Le1 promoter decreases, the effect of the Le3 promoter increases. Similar constructs were also made with all three promoters and including the signal peptides from the three respective genes, fused to gusA, and introduced into Arabidopsis. Reporter gene expression in Arabidopsis transformed with the constructs containing the signal peptides showed the same patterns as those that resulted from the corresponding constructs without signal peptides. The expression patterns resulting from the three different lectin promoters are distinct and consistent with computational predictions.