Mitochondrial alternative oxidase enhanced ABA-mediated drought tolerance in Solanum lycopersicum

The phytohormone abscisic acid (ABA) plays essential roles in modulating drought stress responses. Mitochon-drial alternative oxidase (AOX) is critical for reactive oxygen species (ROS) scavenging in drought stress re-sponses. However, whether ABA signal in concert with AOX to moderate drought stress response remains largely unclear. In our study, we uncover the positive role of AOX in ABA-mediated drought tolerance in tomato (So-lanum lycopersicum). Here, we report that ABA participates in the regulation of alternative respiration, and the increased AOX was found to improve drought tolerance by reducing total ROS accumulation. We also found that transcription factor ABA response element-binding factor 1 (SlAREB1) can directly bind to the promoter of AOX1a to activate its transcription. Virus-induced gene silencing (VIGS) of SlAREB1 compromised the ABA-induced alternative respiratory pathway, disrupted redox homeostasis and decreased plant resistance to drought stress, while overexpression of AOX1a in TRV2-SlAREB1 plants partially rescued the severe drought phenotype. Taken together, our results indicated that AOX1a plays an essential role in ABA-mediated drought tolerance partially in a SlAREB1-dependent manner, providing new insights into how ABA modulates ROS levels to cope with drought stress by AOX.

Automated summary

The phytohormone abscisic acid (ABA) and mitochondrial alternative oxidase (AOX) both contribute to drought stress responses in tomato. ABA regulates alternative respiration and increasing AOX enhances drought tolerance by reducing reactive oxygen species (ROS) accumulation. The transcription factor SlAREB1 directly activates the transcription of AOX1a and its silencing compromises ABA-induced alternative respiration, leading to decreased resistance to drought stress. These findings provide new insights into the role of AOX in ABA-mediated drought tolerance.