MsPG3 polygalacturonase promoter elements necessary for expression during Sinorhizobium meliloti–Medicago truncatula interaction

MsPG3 is a Medicago sativa polygalacturonase gene isolated in our laboratory, its expression during nodule development is associated with the presence of Sinorhizobium meliloti. By RT-PCR and in situhybridization studies we showed the early induction of MsPG3 expression after inoculation of M. sativaplants with the microsymbiont, suggesting a role for MsPG3 product in the early stages of the interaction. To localize its expression in nodule as well as to characterize the transcriptional regulation of MsPG3, Medicago truncatula transgenic plants containing a 2.7 kb MsPG3 promoter-(beta)-glucuronidase (gus)gene fusion have been obtained. These transgenic plants showed nodule-specific gusexpression pattern. Five MsPG3 promoter fragments of different length (from 600 to 92 bp) fused to gusgene have been used to transform M. truncatula in order to determine the promoter regions responsible of this nodule specificity. The region between 600 and 413 bp of MsPG3 promoter was found necessary for transgenic gusexpression in nodules. This result was also confirmed in V. hirsuta transgenic `hairy rootsʹ. At position –474/–492 bp upstream of the start codon a sequence was identified that is homologous to the binding site of the transcription factor ENBP1. Our results suggest that MsPG3 expression in nodules could be regulated through this element.