Hydrogen Sulfide modulates Flagellin-Induced Stomatal Immunity

Stomata are natural pores through which plants exchange gases with the environment, mainly carbon dioxide and oxygen required for photosynthesis and respiration, as well as water vapor through evapotranspiration. However, they also serve as entry points for microbial pathogens such asPseudomonas syringaepv. tomato(Pst) bacteria. To prevent microbe invasion, guard cells detect pathogens-associated molecular patterns (PAMPs), including the bacterial peptide flagellin (flg22), triggering stomatal closure. This study identifies hydrogen sulfide (H₂S) and its cytosolic source L-CYSTEINE DESULFHIDRASE 1 (DES1), as key players in stomatal immunity. We demonstrate that H₂S and DES1 are involved in flg22- and bacterial-induced responses, including stomatal closure and modulation of reactive oxygen species (ROS) production. We have found that knock out mutants inDES1gene exhibits reduced susceptibility toPstspray-inoculation and lower apoplastic and cytosolic H₂O₂levels in response to flg22. Additionally, H₂S independently induces cytosolic H₂O₂levels in guard cells without requiring RBOHD activity. All together, these findings establish H₂S and its source, DES1, as critical components of the stomatal immune response.