Candidate gene mapping reveals VrMLO12 (MLO Clade II) is associated with powdery mildew resistance in mungbean (Vigna radiata [L.] Wilczek).
Loss/reduction of function of Mildew Locus O (MLO) genes clade V and MLO clade IV has been shown to be responsible for powdery mildew (PM) resistance in several plant species. Mungbean (Vigna radiata) genome possesses 18 MLO genes, VrMLO1 - VrMLO18. A previous study using mungbean F2 and BC1F1 populations derived from a cross between "CN60″ (susceptible) and "RUM5″ (resistance) demonstrated that QTL qPMRUM5-3 is a major QTL for PM resistance caused by Erysiphe polygoni and is the same with major QTL qPMV4718-3 that confers PM resistance in "V4718″ (resistance). In this study, bioinformatics analysis revealed VrMLO12 locates in the qPMRUM5-3 region. Fine mapping in the F2 and BC1F1 populations using newly developed DNA markers including gene-specific markers demonstrated association between VrMLO12 and the PM resistance. Sequence analyses of VrMLO12 revealed that compared to susceptible mungbeans, RUM5 and V4718 possess SNPs in exon 10 and exon 13. The SNPs caused amino acid changes of VrMLO12, A387S and A476 G, respectively. The change occurred in transmembrane 6 domain and calmodulin binding domain (CaMBD) of the VrMLO12 protein, respectively. qRT-PCR showed that transcript expression level of VrMLO12 in RUM5 challenged with and without by E. polygoni was significantly higher than that in CN60. Phylogenetic analysis revealed that in contrast to previous findings that MLO proteins associated with PM resistance belong to MLO clade V and MLO clade IV, VrMLO12 belongs to MLO clade II. The result suggested that VrMLO12 may function differently from the other MLOs that associated with PM susceptibility. Our findings provide insight into the PM resistance in mungbean and tools for mungbean breeding.
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