The Roles Of S-Nitrosoglutathione Reductase In Regulating Cell Death In N. Tabacum

GSNOR1 (S-nitrosoglutathione reductase) is the key enzyme that regulates cellular levels of S-nitrosylation across kingdoms. However, the role of GSNOR1 in Nicotiana species has not been investigated previously. To study the role of GSNOR1 in cell death and disease resistance in Nicotiana species, transgenic RNAi lines were generated in N. tabacum cv Samsun either carrying or not carrying a TMV resistant gene, N. To our surprise, we found that spontaneous cell death occurred on the leaves of N. tabacum regardless of N gene presence, suggesting that GSNOR1 negatively regulates cell death in Nicotiana species. Unlike strictly restricted to the infiltrated area of wild type leaves, hypersensitive response (HR) triggered by incompatible interactions artificially created by agro-infiltration of p50, an elicitor of TMV N gene product, and active Pto, can be spread to un-infiltrated area in the leaves of N. tabacum RNAi plants, suggesting that biotic stress can accelerate the spread of cell death on GSNOR1-silenced plants. Both nitric oxide (NO) and H2O2 were over-accumulated in the NtGSNOR1-silenced leaves, implying that the cell death on the NbGSNOR1 RNAi lines could be a results of interactions between over-accumulated NO and H2O2. Moreover, MAP kinases, including MPK6, MPK3 and MPK4, and Pathogenesis-related genes (PR genes) are activated and induced, respectively, in the local leaves with ongoing cell death but not in the upper systemic leaves without cell death of these RNAi lines. Consistent with the constitutively activated defense response, the basal and N gene-mediated resistance to Tobacco mosaic virus (TMV)was significantly enhanced in the NtGSNOR1-silenced plants. In sharp contrast to naturally occurred cell death under normal growth conditions, the NtGSNOR1 RNAi lines were more resistant to paraquat-induced cell death compared to WT. Together, our results indicate that GSNORl in Nicotiana species functions as both positive and negative regulator of cell death under different cellular conditions.