H2S generated by L-cysteine desulfhydrase (SlLCD1) enhances heat tolerance in tomato via antioxidant capacity and stomatal modulation.

Global warming is increasing the frequency of heat stress, a major abiotic constraint on crop growth and productivity. Hydrogen sulfide (H2S), a novel gasotransmitter, has been reported to enhance crops' heat tolerance, yet its underlying mechanism remains poorly understood. Here, we provide genetic evidence confirming that L-cysteine desulfhydrase (SlLCD1, Solyc01g068160) was the enzymatic source of endogenous H2S in tomato heat adaptation. Dual activation of H2S signaling through both SlLCD1 overexpression and exogenous application enhanced tomato heat tolerance. Conversely, CRISPR/Cas9-generated SlLCD1 mutants (cr-sllcd1), deficient in heat-induced H2S production, displayed heightened heat sensitivity with accelerated wilting and increased oxidative damage, which was rescued by exogenous H2S application. Compared to wild-type plants, the mutants showed a compromised heat-induced increase in antioxidant enzyme activities and levels. This defect, along with the concomitant ROS accumulation and oxidative damage, was reversed by H2S pretreatment, underscoring the critical role of the SlLCD1-H2S module in maintaining ROS homeostasis during heat adaptation. Additionally, cr-sllcd1 mutants exhibited attenuated heat-induced stomatal closure and increased stomatal density. H2S pretreatment rescued both of these defects, thereby optimizing the trade-off among transpirational cooling, water conservation, and photosynthetic efficiency. Overall, the SlLCD1-H2S module confers heat tolerance by a dual mechanism, coordinately enhancing antioxidant capacity and fine-tuning stomatal dynamics. Our study elucidates an important component of the H2S signaling pathway in plant heat tolerance and offers a promising tractable target for developing heat-tolerant tomato cultivars.