Analysis of genes encoding modular nodulins from Vicia hirsuta and Vicia faba

Abstract

The expression of genes encoding modular nodulins was analysed in the Vicia hirsuta and the Vicia faba system. From V. hirsuta root nodules, we isolated two families of transcript sequences designated VhNOD28/32-A and VhNOD28/32-B encoding nodulins homologous to the V. faba nodulins Nvf-28/32 and the Medicago sativa nodulin-25. The modular proteins encoded by the V. hirsuta transcript sequences consisted of N- and C-terminal unique modules flanking two types of repetitive modules. Specific repetitive modules were deleted from individual VhNOD28/32 transcripts. Southern hybridizations indicated the presence of either a small VhNOD28/32 gene family or a single copy gene comprising at least two alleles. VhNOD28/32 transcripts were expressed specifically in root nodules, where they were localized in the nitrogen-fixing zone III. In the Vicia faba system, we isolated the promoter of two alleles of the VfNOD28/32 gene by PCR-based DNA walking. The promoter sequences were similar to the promoter of the M. sativa nodulin-25 gene and contained an organ-specific element at position −68/−55 from the transcriptional start. An analysis of transgenic V. hirsuta root nodules expressing the gusAint reporter gene under the control of the two VfNOD28/32 promoters demonstrated that both promoters were active in the central region of transgenic V. hirsuta nodules.