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 (HS) as an important signal in plant development and adaptation to environmental stress. HS has been proven to participate in ethylene-induced stomatal closure, but how the signaling pathways of HS and ethylene interact is still unclear. Here, we reveal how HS controls the feedback-regulation of ethylene biosynthesis in tomato () under osmotic stress. We found that ethylene induced the production of HS in guard cells. The supply of hypotaurine (HT; a HS scavenger) or DL-pro-pargylglycine (PAG; a synthetic inhibitor of HS) removed the effect of ethylene or osmotic stress on stomatal closure. This suggests that ethylene-induced HS is a downstream component of osmotic stress signaling, which is required for ethylene-induced stomatal closure under osmotic stress. We further found that HS 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 HS 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 HS negatively regulates ethylene biosynthesis by persulfidation of LeACOs. In addition, HS was also found to inhibit the expression of genes. The results provide insight on the general mode of action of HS and contribute to a better understanding of a plant's response to osmotic stress.