Genetic elucidation of hydrogen signaling in plant osmotic tolerance and stomatal closure via hydrogen sulfide.

Although ample evidence showed that exogenous hydrogen gas (H2) controls a diverse range of physiological functions in both animals and plants, the selective antioxidant mechanism, in some cases, is questioned. Importantly, most of the experiments on the function of H2 in plants were based on pharmacological approaches due to the synthesis pathway(s) in plants are still unclear. Here, we observed that the seedling growth inhibition of Arabidopsis caused by low doses of mannitol could progressively recover by recuperation, accompanied with the increased hydrogenase activity and H2 synthesis. To investigate the functions of endogenous H2, a hydrogenase gene (CrHYD1) for H2 biosynthesis from Chlamydomonas reinhardtii was expressed in Arabidopsis. Transgenic plants could intensify higher H2 synthesis compared with wild type and Arabidopsis transformed with the empty vector, and exhibited enhanced osmotic tolerance in both germination and post-germination stages. In response to mannitol, transgenic plants enhanced L-Cys desulfhydrase (DES)-dependent hydrogen sulfide (H2S) synthesis in guard cells and thereafter stomatal closure. The application of des mutant further highlights H2S acting as a downstream molecule of endogenous H2 control of stomatal closure. These results thus open a new window for increasing plant tolerance to osmotic stress.