Mitochondrial alternative oxidase‐dependent autophagy involved in ethylene‐mediated drought tolerance in Solanum lycopersicum

Summary Mitochondrial alternative oxidase ( AOX ) is involved in a large number of plant physiological processes, such as growth, development and stress responses; however, the exact role of AOX in response to drought remains unclear. In our study, we provide solid evidences that the activated AOX capacity positively involved in ethylene‐induced drought tolerance, in tomato ( Solanum lycopersicum ), accompanied by the changing level of hydrogen peroxide (H 2 O 2 ) and autophagy. In AOX 1a ‐ RNA i plants, the ethylene‐induced drought tolerance was aggravated and associated with decreasing level of autophagy. The H 2 O 2 level was relatively higher in AOX 1a ‐ RNA i plants, whereas it was lower in AOX 1a ‐overexpressing (35S‐ AOX 1a‐ OE ) plants after 1‐(aminocarbonyl)‐1‐cyclopropanecarboxylic acid ( ACC ) pretreatment in the 14th day under drought stress. Interestingly, the accumulation of autophagosome was accompanied by the changing level of reactive oxygen species ( ROS ) in AOX transgenic tomato under drought stress whether or not pretreated with ACC . Pharmacological scavenging of H 2 O 2 accumulation in AOX 1a ‐ RNA i ( aox19 ) stimulated autophagy acceleration under drought stress, and it seems that AOX ‐dependent ROS signalling is critical in triggering autophagy. Lower levels of ROS signalling positively induce autophagy activity, whereas higher ROS level would lead to rapid programmed cell death ( PCD ), especially in ethylene‐mediated drought tolerance. Moreover, ethylene‐induced autophagy during drought stress also can be through ERF 5 binding to the promoters of ATG 8d and ATG 18h . These results demonstrated that AOX plays an essential role in ethylene‐induced drought tolerance and also played important roles in mediating autophagy generation via balancing ROS level.