Hydrogen sulfide persulfidates OAS-A1 to balance cysteine levels in regulating Arabidopsis stomatal development.

Plants regulate photosynthesis and transpiration primarily by adjusting the stomatal aperture and density to adapt to environmental changes. O-acetylserine(thiol)lyase (OAS-TL) maintains a balance between cysteine (Cys) and sulfide metabolism. Here, we report that OAS-TL plays a critical role in stomatal development in Arabidopsis thaliana. Mutations in the OAS-TL family member gene OAS-A1 reduce Cys synthesis, leading to increased stomatal density and reduced plant drought tolerance. Moreover, hydrogen sulfide (H2S) enhances the enzymatic activity of OAS-A1 by persulfidating the Cys28 and Cys42 residues in vitro and in vivo, thereby promoting the catalytic synthesis of Cys directly and glutathione (GSH) indirectly. Deletion of Cys28 and Cys42 in OAS-A1 leads to reduced GSH levels and elevates hydrogen peroxide (H2O2) accumulation, consequently increasing stomatal density. Together, our data demonstrate that OAS-A1 affects H2O2 and GSH levels by catalyzing Cys synthesis to regulate stomatal development, highlighting the role of H2S-triggered persulfidation on OAS-A1 activity during this process.