Catalases may play different roles in influencing resistance to virus-induced hypersensitive necrosis

Abstract

High concentrations of the reactive oxygen species (ROS) superoxide (O2•−) and hydrogen peroxide (H2O2) contribute to the induction of plant cell and tissue death (necrosis). In an effort to create transgenic plants with high antioxidant capacity that could resist necrotic symptoms we produced two transgenic tobacco (Nicotiana tabacum cv. SR1) lines (S1 and S2) overexpressing a tomato chloroplast superoxide dismutase (SlChSOD). SOD genes encode for antioxidant enzymes that dismutate superoxide to hydrogen peroxide. Therefore, SOD-overproducing plants may contain high levels of hydrogen peroxide and are sensitive to stress-related necrosis unless sufficient degradation of hydrogen peroxide is conferred by elevated expression of antioxidants like e.g. catalases and peroxidases. Indeed, line S1 displayed elevated expression of a glutathione peroxidase (NtGPX) and a glutathione S-transferase (NtGSTU1b), as compared to wild type plants. Interestingly, however, expression of a catalase (NtCAT1) was repressed in both SOD-overexpressing lines. This predicts that such plants could be sensitive to localized necrosis (HR) caused by virus infection, since repression of NtCAT1 has been shown to occur during virus-induced HR (e.g. Dorey et al., 1998; Künstler et al., 2007). To elucidate whether other catalases might play a role in resistance to virus induced HR-type necrotic symptoms, a maize catalase (ZmCat2) was transiently overexpressed in Nicotiana edwardsonii and N. edwardsonii var. Columbia plants by agroinfiltration. Inoculation of agroinfiltrated plants with Tobacco mosaic virus (TMV) revealed that ZmCat2 confers enhanced resistance to HR-type necrosis during TMV infection. It seems that catalases may play different roles in influencing resistance to virus-induced hypersensitive necrosis.