Systemic induction and role of mitochondrial alternative oxidase and nitric oxide in a compatible tomato-tobacco mosaic virus interaction

Abstract

The role of mitochondrial alternative oxidase (AOX) and the relationship between AOX and nitric oxide (NO) in virusinduced systemic defense to Tobacco mosaic virus (TMV) were investigated in susceptible tomato (Solanum lycopersi- cum) plants. TMV inoculation to the lower leaves induced a rapid NO synthesis and AOX activation in upper uninocu- lated leaves as early as 0.5 day postinoculation. Application of exogenous potassium cyanide (KCN, a cytochrome path- way inhibitor) at nonlethal concentrations and NO donor diethylamine NONOate (DEA/NO) to the upper uninocu- lated leaves greatly induced accumulation of AOX transcript, reduced TMV viral RNA accumulation, and increased the leaf photochemical quantum yield at photosystem II. Pretreatment with NO scavenger almost completely blocked TMV-induced AOX induction and substantially increased TMV susceptibility. Salicylhydroxamic acid (SHAM, an AOX inhibitor) pretreatment reduced the DEA/NO-induced cyanide-resistant respiration and par- tially compromised induced resistance to TMV. Conversely, KCN and SHAM pretreatment had very little effect on gen- eration of NO, and pretreatment with NO scavenger did not affect KCN-induced AOX induction and TMV resistance. These results suggest that TMV-induced NO generation acts upstream and mediates AOX induction which, in turn, in- duces mitochondrial alternative electron transport and triggers systemic basal defense against the viral pathogen. © 2010 The American Phytopathological Society.