Ethylene is involved in leafy mustard systemic resistance to Turnip mosaic virus infection through the mitochondrial alternative oxidase pathway

The role of the mitochondrial alternative oxidase (AOX) pathway and the relationship between AOX and ethylene in resistance to Turnip mosaic virus (TuMV) were investigated in systemic infected mustard leaves. Expressions of AOX1a and ethylene biosynthesis-related genes were enhanced in the upper uninoculated leaves at 6 days of postinoculation (dpi). Increased accumulation of AOX1a transcript and reduced levels of TuMV-CP were also observed after pretreatment with AA (a cytochrome pathway inhibitor) or ACC (an ethylene precursor) at non-lethal concentrations. Meanwhile, application of AVG (an ethylene biosynthesis inhibitor) mostly blocked TuMV-induced AOX activity and substantially increased TuMV susceptibility in the upper leaves. SHAM (AOX pathway inhibitor) pretreatment partially reduced the ACC-induced cyanide-resistant respiration and TuMV resistance. Conversely, AA and SHAM pretreatments had little effect on generation of ethylene. These results suggested that the TuMV-induced increase of AOX was partly involved in the ethylene pathway, and ethylene unregulated AOX in upper uninoculated mustard leaves.

► The AOX and ET were enhanced by TuMV infection in the systemic mustard leaves.
► ET accumulation could increase the activity of AOX pathway.
► Enhanced activity of AOX had no significantly influence to the ET biosynthesis.
► The systemic resistance induced by AOX may involve in the ET defense pathway.