Nuclear factors interact with conserved A/T-rich elements upstream of a nodule-enhanced glutamine synthetase gene from french bean

Abstract

The gln-γ gene, encoding the γ subunit of glutamine synthetase in French bean (Phaseolus vulgaris) is strongly induced during nodule development. We have determined the nucleotide sequence of a 1.3-kilobase region at its 5′ end and have identified several sequences common to the promoter regions of late nodulin genes from other legume species. The 5′-flanking region was analyzed for sequence-specific interactions with nuclear factors from French bean. A factor from nodules (PNF-1) was identified that binds to multiple sites between -860 and -154 and a related but distinct factor (PRF-1) was detected in extracts from uninfected roots. PNF-1 and PRF-1 bound strongly to a synthetic oligonucleotide containing the sequence of an A/T-rich 21-base pair imperfect repeat found at positions -516 and -466. The same factors also had a high affinity for a protein binding site from a soybean leghemoglobin gene and appeared to be closely related to the soybean nodule factor NAT2, which binds to A/T-rich sequences in the lbc3 and nodulin 23 genes [Jacobsen et al. (1990). Plant Cell 2, 85-94]. Comparison of NAT2/ PNF-1 binding sites from a variety of nodulin genes revealed the conservation of the short consensus core motif TATTTWAT, and evidence was obtained that this sequence is important for protein recognition. Cross-recognition by PNF-1 of a protein binding site in a soybean seed protein gene points to the existence of a ubiquitous family of factors with related binding affinities. Our data suggest that PNF-1 and PRF-1 belong to an evolutionary conserved group of nuclear factors that interact with specific A/T-rich sequences in a diverse set of plant genes. We consider the possible role of these factors in coregulating the expression of gln-γ and other late nodulin genes.