Minimal enhancer elements of the leghemoglobin lba and lbc3 gene promoters from Glycine max L. have different properties

A novel type of DNA-binding protein interacts with a conserved sequence in an early nodulin ENOD12 promoter

The pea genes PsENOD12A and PsENOD12B are expressed in the root hairs shortly after infection with the nitrogen-fixing bacterium Rhizobium leguminosarum bv. viciae or after application of purified Nod factors. A 199 bp promoter fragment of the PsENOD12B gene contains sufficient information for Nod factor-induced tissue-specific expression. We have isolated a Vicia sativa cDNA encoding a 1641 amino acid protein, ENBP1, that interacts with the 199 bp ENOD12 promoter. Two different DNA-binding domains were identified in ENBP1. A domain containing six AT-hooks interacts specifically with an AT-rich sequence located between positions -95 and -77 in the PsENOD12B promoter. A second domain in ENBP1 is a cysteine-rich region that binds to the ENOD12 promoter in a sequence non-specific but metal-dependent way. ENBP1 is expressed in the same cell types as ENOD12. However, additional expression is observed in the nodule parenchyma and meristem. The presence of three small overlapping ORFs in the 5'-untranslated region of the ENBP1 cDNA indicates that ENBP1 expression might be regulated at the translational level. The interaction of ENBP1 with a conserved AT-rich element within the ENOD12 promoter and the presence of the ENBP1 transcript in cells expressing ENOD12 strongly suggest that ENBP1 is a transcription factor involved in the regulation of ENOD12. Finally, the C-terminal region of ENBP1 shows strong homology to a protein from rat that is specifically expressed in testis tissue.

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 glycine-rich early nodulin. This gene was predominantly expressed in the interzone II-III region of Vicia faba root nodules. The VfENOD-GRP3 promoter contained several sequence motifs potentially involved in the regulation of gene expression. To investigate the molecular basis for the specific VfENOD-GRP3 expression, defined VfENOD-GRP3 promoter fragments were fused to an intron-containing gusAint gene. Agrobacterium rhizogenes ARqual strains carrying these fusions integrated into the TL DNA were used to generate hairy roots on Vicia hirsuta, which subsequently were nodulated. Histochemical analysis of transgenic nodules indicated that a strong gusAint expression in the interzone II-III region was mediated by the -1252/+10 VfENOD-GRP3 promoter region. This reporter gene expression in V. hirsuta was comparable to the location of VfENOD-GRP3 transcripts in V. faba nodules. An analysis of defined promoter fragments revealed that a strong gusAint expression in the interzone II-III region was also mediated by the -737/+10 promoter, whereas the -239/+10 promoter only mediated a weak gusAint expression in the interzone II-III region. Since the -239/+10 promoter fragment did not resemble published nodulin gene promoters, we propose that it contains new sequence motifs involved in mediating gene expression in the interzone II-III region of Vicia nodules.

A 200 bp region of the pea ENOD12 promoter is sufficient for nodule-specific and nod factor induced expression

ENOD12 is one of the first nodulin genes expressed upon inoculation with Rhizobium and also purified Nod factors are able to induce ENOD12 expression. The ENOD12 gene family in pea (Pisum sativum) has two members. A cDNA clone representing PsENOD12A [26] and a PsENOD12B genomic clone [7] have been previously described. The isolation and characterization of a PsENOD12A genomic clone is presented in this paper. By using a Vicia hirsuta-Agrobacterium rhizogenes transformation system it is shown that both genes have a similar expression pattern in transgenic V. hirsuta root nodules. Promoter analyses of both PsENOD12 promoters showed that the 200 bp immediately upstream of the transcription start are sufficient to direct nodule-specific and Nod factor-induced gene expression.

Analysis of the lupin Nodulin-45 promoter: conserved regulatory sequences are important for promoter activity

The promoter from the Lupinus angustifolius late nodulin gene, Nodulin-45, has been analysed to identify cis-elements and trans-acting factors. Various regions of the Nodulin-45 promoter, fused to the luciferase reporter gene, were introduced into Lotus roots using an Agrobacterium rhizogenes, transformation procedure. The transgenic roots were then nodulated. The promoter region A (-172 to +13, relative to the transcription start site) was capable of directing low-level expression of the reporter gene and in a nodule-enhanced manner when compared to roots. The addition of region C (-676 to -345) resulted in a significant increase in the expression within the nodule, whilst a low level of root expression was maintained. The C region, which confers this high-level nodule expression, contains the nodule consensus motifs AAAGAT and CTCTT. When region C was ligated to a minimal promoter element from the unrelated asparaginase gene rather than the Nodulin-45 A region, nodule-enhanced expression was still apparent, but at a much lower level. Mutation of the AAAGAT element in this construct resulted in a further significant decrease of expression. Gel retardation assays revealed that a factor from lupin nodule nuclear extracts interacted with two sequences of the C region. The binding of the factor to both of these regions could be removed by the addition of an oligonucleotide containing the AT-rich binding site for the soybean factor NAT2. This suggests that the lupin factor identified here is a NAT2 homologue. No factor binding was observed to the AAAGAT or CTCTT elements present in the C region.

The expression of a chimeric Phaseolus vulgaris nodulin 30-GUS gene is restricted to the rhizobially infected cells in transgenic Lotus corniculatus nodules

In Phaseolus vulgaris there is a nodulin family, Npv30, of ca. 30 kDa, as detected in an in vitro translation assay [2]. We isolated a gene (npv30-1) for one of the members of this family. The nucleotide sequence of the promoter of npv30-1 contains nodule-specific motifs common to other late nodulin genes. The promoter was fused to the GUS reporter gene; this chimeric fusion was introduced into Lotus corniculatus via Agrobacterium rhizogenes transformation. GUS activity was only detected in the infected cells of the nodules of transgenic plants. By contrast, the expression of a 35S-GUS construct was restricted to the uninfected cells and the vascular tissue.