Melatonin-induced cold and drought tolerance is regulated by brassinosteroids and hydrogen peroxide signaling in perennial ryegrass

Abstract

Perennial ryegrass (Lolium perenne L.) is widely used as cool-season turfgrass; however, its growth is mainly limited by cold and drought stress. The interplay between melatonin and brassinosteroids in enhancing tolerance to cold and drought stress and their underlying molecular mechanisms is poorly understood so far. In this study, melatonin enhanced cold and drought tolerance in perennial ryegrass depended on the duration of dose and the level of stress. Although melatonin activates the expression of NADPH oxidase-related genes post-exposure to short-term cold/drought stresses, the accumulation of H2O2 was reduced under long-term stress. This increase in antioxidant activity was correlated with an increase of genes expressed in their antioxidant system and ascorbate-glutathione cycle. Moreover, the exogenous melatonin induced the biosynthesis of melatonin and brassinosteroids or the expression of signaling-related genes. However, the expression of brassinosteroids biosynthesis and signaling-related genes were inhibited in the rbohC and rbohF mutants in the presence of melatonin. The inhibition of H2O2 production attenuated melatonin-mediated growth in the Arabidopsis wild-type as well as bak1 and bri1.9 mutants. DMTU inhibited the mitigation effect of melatonin on the H2O2 accumulation in WT and LpBAK1 transgenic plants, while a lighter DAB staining was observed in the LpBAK1 transgenic seedlings. Consistently, the chemical scavenging of H2O2 impaired the effect of melatonin as well as brassinosteroids on seed germination and the root growth of perennial ryegrass. The current study reveals a novel regulatory mechanism of the crosstalk between H2O2 and brassinosteroid signaling in melatonin-induced cold/drought tolerance in perennial ryegrass.