Molecular and biochemical characterization of a Vigna mungo MAP kinase associated with Mungbean Yellow Mosaic India Virus infection and deciphering its role in restricting the virus multiplication.

Yellow Mosaic Disease caused by the begomovirus Mungbean Yellow Mosaic India Virus (MYMIV) severely affects many economically important legumes. Recent investigations in Vigna mungo - MYMIV incompatible interaction identified a MAPK homolog in the defense signaling pathway. An important branch of immunity involves phosphorylation by evolutionary conserved Mitogen-activated protein kinases (MAPK) that transduce signals of pathogen invasion to downstream molecules leading to diverse immune responses. However, most of the knowledge of MAPKs is derived from model crops, and functions of these versatile kinases are little explored in legumes. Here we report characterization of a MAP kinase (VmMAPK1), which was induced upon MYMIV-inoculation in resistant V. mungo. Phylogenetic analysis revealed that VmMAPK1 is closely related to other plant-stress-responsive MAPKs. Both mRNA and protein of VmMAPK1 were accumulated upon MYMIV infection. The VmMAPK1 protein localized in the nucleus as well as cytoplasm and possessed phosphorylation activity in vitro. A detailed biochemical characterization of purified recombinant VmMAPK1 demonstrated an intramolecular mechanism of autophosphorylation and self-catalyzed phosphate incorporation on both threonine and tyrosine residues. The Vmax and Km values of recombinant VmMAPK1 for ATP were 6.292nmol/mg/min and 0.7978μM, respectively. Furthermore, the ability of VmMAPK1 to restrict MYMIV multiplication was validated by its ectopic expression in transgenic tobacco. Importantly, overexpression of VmMAPK1 resulted in the considerable upregulation of defense-responsive marker PR genes. Thus, the present data suggests the critical role of VmMAPK1 in suppressing MYMIV multiplication presumably through SA-mediated signaling pathway and inducing PR genes establishing the significant implications in understanding MAP kinase gene function during Vigna-MYMIV interaction; and hence paves the way for introgression of resistance in leguminous crops susceptible to MYMIV.