THE PROMOTER OF THE VICIA-FABA L VFENOD-GRP3 GENE ENCODING A GLYCINE-RICH EARLY NODULIN MEDIATES A PREDOMINANT GENE-EXPRESSION IN THE INTERZONE II-III REGION OF TRANSGENIC VICIA-HIRSUTA ROOT-NODULES

We recently reported on the broad bean gene VfENOD-GRP3 encoding a gly cine-rich early nodulin. This gene was predominantly expressed in the interzone II-III region of Vicia faba root nodules. The VfENOD-GRP3 pr omoter contained several sequence motifs potentially involved in the r egulation of gene expression. To investigate the molecular basis for t he specific VfENOD-GRP3 expression, defined VfENOD-GRP3 promoter fragm ents were fused to an intron-containing gusAint gene. Agrobacterium rh izogenes ARqual strains carrying these fusions integrated into the TL DNA were used to generate hairy roots on Vicia hirsuta, which subseque ntly were nodulated. Histochemical analysis of transgenic nodules indi cated that a strong gusAint expression in the interzone II-III region was mediated by the -1252/+10 VfENOD-GRP3 promoter region. This report er gene expression in V. hirsuta was comparable to the location of VfE NOD-GRP3 transcripts in V. faba nodules. An analysis of defined promot er fragments revealed that a strong gusAint expression in the interzon e II-III region was also mediated by the -737/+10 promoter, whereas th e -239/+10 promoter only mediated a weak gusAint expression in the int erzone II-III region. Since the -239/+10 promoter fragment did not res emble published nodulin gene promoters, we propose that it contains ne w sequence motifs involved in mediating gene expression in the interzo ne II-III region of Vicia nodules.