Ethylene-Induced Hydrogen Sulfide Negatively Regulates Ethylene Biosynthesis by Persulfidation of ACO in Tomato Under Osmotic Stress

A number of recent studies identified hydrogen sulfide (H ₂S) as an important signal in plant development and adaptation to environmental stress. H ₂S has been proven to participate in ethylene-induced stomatal closure, but how the signaling pathways of H ₂S and ethylene interact is still unclear. Here, we reveal how H ₂S controls the feedback-regulation of ethylene biosynthesis in tomato ( Solanum lycopersicum) under osmotic stress. We found that ethylene induced the production of H ₂S in guard cells. The supply of hypotaurine (HT; a H ₂S scavenger) or DL-pro-pargylglycine (PAG; a synthetic inhibitor of H ₂S) removed the effect of ethylene or osmotic stress on stomatal closure. This suggests that ethylene-induced H ₂S is a downstream component of osmotic stress signaling, which is required for ethylene-induced stomatal closure under osmotic stress. We further found that H ₂S inhibited ethylene synthesis through inhibiting the activity of 1-aminocyclopropane-1-carboxylic acid (ACC) oxidases (ACOs) by persulfidation. A modified biotin-switch method (MBST) showed that H ₂S can induce persulfidation of LeACO1 and LeACO2 in a dose-dependent manner, and that persulfidation inhibits the activity of LeACO1 and LeACO2. We also found that LeACO1 is persulfidated at cysteine 60. These data suggested that ethylene-induced H ₂S negatively regulates ethylene biosynthesis by persulfidation of LeACOs. In addition, H ₂S was also found to inhibit the expression of LeACO genes. The results provide insight on the general mode of action of H ₂S and contribute to a better understanding of a plant’s response to osmotic stress.