Hydrogen sulfide alleviates osmotic stress‐induced root growth inhibition by promoting auxin homeostasis

SUMMARY Hydrogen sulfide (H 2 S) promotes plant tolerance against various environmental cues, and d ‐cysteine desulfhydrase (DCD) is an enzymatic source of H 2 S to enhance abiotic stress resistance. However, the role of DCD‐mediated H 2 S production in root growth under abiotic stress remains to be further elucidated. Here, we report that DCD‐mediated H 2 S production alleviates osmotic stress‐mediated root growth inhibition by promoting auxin homeostasis. Osmotic stress up‐regulated DCD gene transcript and DCD protein levels and thus H 2 S production in roots. When subjected to osmotic stress, a dcd mutant showed more severe root growth inhibition, whereas the transgenic lines DCDox overexpressing DCD exhibited less sensitivity to osmotic stress in terms of longer root compared to the wild‐type. Moreover, osmotic stress inhibited root growth through repressing auxin signaling, whereas H 2 S treatment significantly alleviated osmotic stress‐mediated inhibition of auxin. Under osmotic stress, auxin accumulation was increased in DCDox but decreased in dcd mutant. H 2 S promoted auxin biosynthesis gene expression and auxin efflux carrier PIN‐FORMED 1 (PIN1) protein level under osmotic stress. Taken together, our results reveal that mannitol‐induced DCD and H 2 S in roots promote auxin homeostasis, contributing to alleviating the inhibition of root growth under osmotic stress.