Expression analysis of MAP K 4 and MAP K 6 during pathogenesis of Alternaria blight in susceptible and tolerant genotypes of Brassica juncea

Transcript profiling and immunodetection of MAPK4 and MAPK6 proteins were carried out at different stages of Alternaria blight disease in Varuna (susceptible) and PAB 9511 (tolerant) genotypes of Brassica juncea to probe the role of these kinases during pathogenesis. The transcripts of both MAPK4 and MAPK6 correlated with their protein products at different stages (viz. initial, middle and late) of infection, however, with few exceptions. It was observed that the expression of MAPK4 is downregulated whereas that of MAPK6 is upregulated as disease progresses through different stages of infection in both genotypes. After correlating the accumulation of transcript or protein product with disease severity, it may be inferred that downregulation of MAPK4 weakens MAPK4 dependent plant defense so as to facilitate the pathogen’s colonization on the Brassica plant. Further, upregulation of MAPK6 suggests strengthening of MAPK6 dependent plant defense which, however, may be insufficient to curtail the pathogen’s colonization as the disease progresses. The increased expression of both kinases in the tolerant genotype of Brassica juncea suggests that MAPK4 or MAPK6 dependent defense is triggered to high magnitude as compared to the susceptible genotype of Brassica juncea. During progression through different stages of infection, the expression of MAPK4 and MAPK6 has shown negative correlations with each other in both genotypes of Brassica.