Author(s): Monika Bisht, Shivanshu Garg, Pooja Nain, Himanshu Punetha and Dinesh Pandey

Abstract: In order to explore the role of salicylic acid mediated defense at different stages of Alternaria blight, the relative transcript expression analysis of MAPK3 and NPR1 was performed on the plants of two ecotypes (WS and Columbia) of Arabidopsis thaliana inoculated distinctly with pathogen, salicylic acid (SA) and salicylic acid pre-conditioning followed by pathogen inoculation. Upon application of SA, the disease index significantly reduced in both ecotypes in response to pathogen challenge. Higher expression of MAPK3 and NPR1 was observed at critical stages of disease progression in plants–preconditioned with SA before pathogen inoculation as compared to only pathogen challenged plants of both the ecotypes. This reflects triggering of SA mediated expression of MAPK3, NPR1 dependent defense response against the pathogen. High and rapid induction of this defense pathway in Columbia ecotype contributes to its tolerance to Alternaria blight as compared to WS. Salicylic acid triggered lower expression of MAPK3 and NPR1 in response to pathogen encounter at later stages seems to increase disease severity while compared to early and middle stages. The role of SA in defense through modulation of MAPK3 and NPR1 is visualized as soon as 4 hours after pathogen inoculation. MAPK3 and NPR1 expression levels were upregulated and downregulated in a cyclic fashion in both ecotypes in all treatments. SA thus acts by cyclically upregulating MAP Kinase3 and NPR1 at critical initial and late stages of disease progression. The analysis of real time expression of MAPK3 & NPR 1 gene helps in gaining insights for Alternaria blight pathogenesis in model plant Arabidopsis thaliana.

DOI: 10.33545/26174693.2024.v8.i5a.1055