Differential expression of defense-related genes in chilli pepper infected with anthracnose pathogen Colletotrichum truncatum

Anthracnose disease caused by Colletotrichum truncatum is a major economic constraint to chilli production in the tropical and subtropical regions of the world including India. To understand the molecular mechanisms of defense against anthracnose, we used a differential chilli-C. truncatum system consisting of two cultivars of chilli (Susceptible; Teja Jhal, TJ and resistant; Bhut Jolokia, BJ) and a highly virulent C. truncatum isolate to evaluate the temporal expression of seventeen defense-related genes associated with multiple defense signaling pathways. Quantitative real time PCR demonstrated rapid induction and significant accumulation of jasmonic acid (JA) and ethylene (ET) responsive genes such as plant defensin 1.2, Lypoxygenase 3, Allene oxide synthase and ACC synthase 2 in the resistant cultivar post treatment with C. truncatum. Significant induction of these genes was also realized upon exogenous treatment with JA and ET. The salicylic acid (SA) responsive phenylalanine ammonia-lyase 2 gene was upregulated only under incompatible interaction. Further, the transcript levels of pathogenesis related proteins PR2 and PR5 was significantly higher in the resistant genotype whereas PR1 and PR3 were moderately responsive. In addition, the expression of defense responsive transcription factors increased gradually in the resistant cultivar and remained significantly higher at 9 dpi as opposed to the susceptible one. Combined result analyses revealed that chilli adopts multiple defense strategies in mediating defence responses against the C. truncatum infection. Overall, this work represents a valuable resource for future functional genomics experiments to unravel the molecular mechanisms of host resistance and pathogen virulence in the agriculturally important chilli-C. truncatum pathosystem.