Characterization of harpinXoo induced hypersensitive responses in non host plant, tobacco

Abstract

Harpin proteins encoded by hrp genes are bacterial protein elicitors that can stimulate hypersensitive response (HR) in non-host plants. HR-related pathogen resistance involves a complex form of programmed cell death (PCD). It is increasingly viewed as a key component of the hypersensitive disease response of plants. Currently, the evidence of harpin proteins-induced PCD is deficient though it exhibits phenotypic parallels with HR, and the mechanism of harpin proteins-induced PCD is not well understood. In this study, we demonstrate that harpinXoo protein from Xanthomonas oryzae pv. oryzae of rice bacterial blight expressed and isolated from bacterial cells acted as an agent to induce PCD in infiltrated tobacco plants. Treatment of tobacco leaves with harpinXoo induced typical PCD-related morphological and biochemical changes including cell shrinkage and nuclear DNA degradation. We further analyzed the expression of several genes in signal transduction pathway of PCD in tobacco plants by real-time qRT-PCR analysis using EF-1α as an endogenous control. Our results showed that the expression of NtDAD1 was down-regulated and the expression of BI-1, tpa1 and aox1 was up-regulated following the infiltration of harpinXoo into tobacco leaves. Our data suggest that harpinXoo can induce PCD with the coordination of PCD-related genes in infiltrated tobacco leaves, providing evidence to further investigate the signal transduction pathways of HR and PCD.