BR and H2O2 involve in melatonin-induced tolerance

The interplay between melatonin and brassinosteroids in enhancing tolerance to cold and drought tolerance and underlying molecular mechanisms of this relationship still remains unknown. Here, we demonstrate that melatonin enhanced cold and drought tolerance of perennial ryegrass depends on the dose-and-stress duration applied. The combined physiological and transcriptomic analyses revealed that melatonin pretreatment up-regulated PSII aseembly and light-harvesting complex-related genes expression, resultin in a higher photosynthetic capacity. Melatonin activates the expression of NADPH oxidase-related genes to promote H2O2 producing exposed to the short-term of cold/drought stresses, but reduced their expression levels and H2O2 accumulation under the long-term of stresses. This was associated with increased the enzymatic and non-enzymatic antioxidants activities by regulating their related gene expression and modulating the ascorbate-glutathione cycle and proline and polyamine accumulation under long-term of stresses. Moreover, brassinosteroids participated in melatonin-induced stress tolerance. Further experiments indicated that exogenous melatonin increased melatonin and brassinosteroids biosynthesis or signalling-related genes expression and their levels. Melatonin alleviate the stresses-caused growth inhibition in Arabidopsis WT and bak1 plants but exhibited no obvious improvement in bri1.9 mutants. Melatonin-treated bak1 mutants had increased DAB staining than WT. Inhibition of H2O2 production attenuated melatonin-mediated growth in WT, but bak1 and bri1.9 mutants showed a little sensitivity. Consistently, pretreatment with H2O2 scavenger inhibited the effect of melatonin on seed germination and root growth of perennial ryegrass under cold and drought stresses. This research reveals a novel regulatory mechanism of crosstalk of H2O2 and brassinosteroids signallings in melatonin-induced cold/drought tolerance in perennial ryegrass.