Introgression and Gene Expression Differences Responsible for MYMV Resistance in Mungbean (Vigna radiata L. Wilzek), Ricebean [Vigna umbellata (Thunb.) and its Interspecific Hybrids

Management of yellow mosaic disease in mugbean through introgression of resistant genes from ricebean is the best option for its improvement. Ricebean [Vigna umbellata (Thunb.) a wild relative of mungbean belonging to the subgenus Ceratotropis in the genus Vigna has been reported to possess resistance against MYMV (Monika et al., 2001). In the present work, a PCR strategy was used to amplify resistance gene analogues (RGAs) using degenerative primers designed at the conserved motif of cloned plant NBS–LRR R genes. Semi-quantitative RT-PCR analysis revealed the down-regulation of the N-gene homologue in mungbean and up-regulation in ricebean upon MYMV infection. The multiple sequence alignment of deduced amino acid sequences revealed the presence of kinase-2 (KVLLI/VLDDVD) and kinase-3 (WFGPGSRVIITTRD) conserved motifs of NBS region in five RGA sequences.The putative RGA sequences were characterized by the conservation of glycine (G) residue in between kinase-1 and kinase-2 domain and in addition, the aspartic acid (D) residue at the end of kinase-2 domain revealed that the isolated RGAs belongs to TIR-NBS-LRR family of R genes. Further Phylogenetic analysis of Vigna RGAs showed all RGAs belonged to TIR-NBS-LRR class of R genes. Through AFLP-RGA analysis it was found that about 18% of ricebean alleles were introgressed into resistant RILs. It is the first report of using AFLP-RGA in Vigna species. Efforts are underway to develop SNP markers using transcriptomics tools.