Two tightly linked genes coding for NAD-dependent malic enzyme and dynamin-related protein are associated with resistance to Cercospora leaf spot disease in cowpea (Vigna unguiculata (L.) Walp.).

Cercospora leaf spot (CLS) caused by Cercospora canescens is an important disease of cowpea (Vigna unguiculata). A previous study using an F2 population [CSR12906 (susceptible) × IT90K-59-120 (resistant)] identified a major QTL qCLS9.1 for resistance to CLS. In this study, we finely mapped and identified candidate genes of qCLS9.1 using an F3:4 population of 699 individuals derived from two F2:3 individuals segregating at qCLS9.1 from the original population. Fine mapping narrowed down the qCLS9.1 for the resistance to a 60.6-Kb region on cowpea chromosome 10. There were two annotated genes in the 60.6-Kb region; Vigun10g019300 coding for NAD-dependent malic enzyme 1 (NAD-ME1) and Vigun10g019400 coding for dynamin-related protein 1C (DRP1C). DNA sequence analysis revealed 12 and 2 single nucleotide polymorphisms (SNPs) in the coding sequence (CDS) and the 5' untranslated region and TATA boxes of Vigun10g019300 and Vigun10g019400, respectively. Three SNPs caused amino acid changes in NAD-ME1 in CSR12906, N299S, S488N and S544N. Protein prediction analysis suggested that S488N of CSR12906 may have a deleterious effect on the function of NAD-ME1. Gene expression analysis demonstrated that IT90K-59-120 and CSR12906 challenged with C. canescens showed different expression in both Vigun10g019300 and Vigun10g019400. Taken together, these results indicated that Vigun10g019300 and Vigun10g019400 are the candidate genes for CLS resistance in the cowpea IT90K-59-120. Two derived cleaved amplified polymorphic sequence markers were developed to detect the resistance alleles at Vigun10g019300 and Vigun10g019400 in IT90K-59-120.