Differential Expression of Candidate Genes Involved in Root-Knot Nematode Resistance in Cowpea [Vigna unguiculata (L.) Walp]

Cowpea is an important food legume and essential component of cropping systems in drier regions and marginal areas of the tropics and subtropics. Root-knot nematodes (Meloidogyne spp., RKN) are one of most important nematode pests of crop plants with a diverse host range, including cowpea. Previous studies demonstrated that RKN resistance in cowpea is controlled by different genes with major effects. At least two dominant genes Rk and Rk2 control nematode resistance in cowpea and they are localized in two major QTLs, Rkn-1 and Rkn-2. The aim of the present work was to select candidate genes for RKN resistance identified in the Rkn-2 QTL interval and analyze their differential transcription levels. Candidate gene expression profiles were determined using qPCR in two near-isogenic lines, CB46 NULL (susceptible) and CB46+Rk2 (resistant). Based on BAC physical contigs, four genes underlying QTL Rkn-2 were selected for expression analysis. A TIR-NBS-LRR (RGC1) was induced 3 days after inoculation with M. incognita infective juveniles in the resistant genotype. This gene was expressed constitutively in resistant and susceptible plants, although the basal level of expression was significantly higher in resistant plants. No significant changes were observed for the other three genes tested. Our results suggest a role for RGC1 in the defense response against M. incognita, mainly as part of the inducible defense system. Thus, this gene is a good candidate for a resistance protein active against RKN in cowpea.