Reciprocal relationship between expression of MAP Kinase 4 and MAP Kinase 6 during pathogenesis of Alternaria Blight in Arabidopsis thaliana

Arabidopsis thaliana was shown to be an alternate host plant for the disease, Alternaria blight of Brassica and used as a model plant to delineate the relationship between MAP Kinase 4 (MAPK4) and MAP Kinase 6 (MAPK6) during pathogenesis of Alternaria blight. Reverse Transcriptase Polymerase Chain Reaction (RT-PCR) based approach was used to determine the change in transcript profiling of MAPK4 and MAPK6 in leaves of Arabidopsis thaliana ecotype Columbia during different stages of disease progression of Alternaria blight. It was observed that the expression of MAP kinase 4 decreases whereas that of MAP kinase 6 increases as disease progresses through different stages of infection. Thus an inverse relationship between expression of MAPK4 and MAPK6 was observed during pathogenesis of Alternaria blight in Arabidopsis. Since MAPK4 positively regulates Jasmonic acid (JA) dependent defense, against the necrotrophic pathogens, down regulation of MAPK4 suggests that Alternaria brassicae pathogen perhaps overcomes JA mediated defense to favour it's necrotrophic colonization. Upregulation of MAPK6 which is regulator of basic plant defense indicates host plant responds to pathogen attack by strengthening of basal plant defense which is, however, insufficient to curtail necrotrophic colonization of pathogen.

• Arabidopsis thaliana ecotype Columbia acts as host plant for the disease, Alternaria blight of Brassica crops.

• MAP Kinase 4 is downregulated whereas MAP Kinase 6 is upregulated as disease progresses in Arabidopsis thaliana, representing reciprocal relationship between them.