VuNIP1 (NOD26-like) and VuHSP17.7 gene expression are regulated in response to heat stress in cowpea nodule

In tropical areas, high soil temperatures frequently limit biological nitrogen fixation (BNF) activity in a number of legumes species. In contrast with other legumes growing under BNF, cowpea (Vigna unguiculata) nodules are very resistant to high-temperature stress. However, the molecular basis of nodule heat tolerance remains unclear. In order to identify genes involved in the heat stress response in cowpea nodules a cDNA library was screened with cDNA-AFLP derived probes. Two full-length cDNAs corresponding to a small heat shock protein (VuHSP17.7) and to a Nodulin 26 (VuNIP1) were isolated and characterized. VuHSP17.7 encodes a sHSP family class I protein, and VuNIP1 corresponds to a NOD26-like protein, member of NIP subfamily of plant membrane intrinsic protein (MIP). VuHSP17.7 was highly induced by high-temperature stress in nodule, leaves, flower, and bud flower, and VuNIP1 was repressed in nodule after heat stress. Moreover, the spatial expression pattern of VuNIP1 and VuHSP17.7 differs significantly indicating that distinct signaling pathways under heat stress may regulate the expression of these genes.