Role of melatonin inUV-Bsignalling pathway and-Bstress resistance inArabidopsis thaliana

Melatonin (N-acetyl-5-methoxytryptamine) plays important roles in plant defences against a variety of biotic and abiotic stresses, including UV-B stress. Molecular mechanisms underlying functions of melatonin in plant UV-B responses are poorly understood. Here, we show that melatonin effect on molecular signalling pathways, physiological changes and UV-B stress resistance inArabidopsis. Both exogenous and endogenous melatonin affected expression of UV-B signal transduction pathway genes. Experiments using UV-B signalling component mutantscop1-4andhy5-215revealed that melatonin not only acts as an antioxidant to promote UV-B stress resistance, but also regulates expression of several key components of UV-B signalling pathway, including ubiquitin-degrading enzyme (COP1), transcription factors (HY5, HYH) and RUP1/2. Our findings indicate that melatonin delays and subsequently enhances expression ofCOP1,HY5,HYHandRUP1/2, which act as central effectors in UV-B signalling pathway, thus regulating their effects on antioxidant systems to protect the plant from UV-B stress.