Role of melatonin in UV-B signaling pathway and UV-B stress resistance in Arabidopsis thaliana

Melatonin (N-acetyl-5-methoxytryptamine) plays important roles in plant defenses 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 signaling pathways, physiological changes, and UV-B stress resistance in Arabidopsis. Both exogenous and endogenous melatonin affected expression of UV-B signal transduction pathway genes. Experiments using UV-B signaling component mutants cop1-4 and hy5-215 revealed 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 signaling pathway, including ubiquitin-degrading enzyme (COP1), transcription factors (HY5, HYH), and RUP1/2. Our findings indicate that melatonin delays and subsequently enhances expression of COP1, HY5, HYH, and RUP1/2, which act as central effectors in UV-B signaling pathway, thus regulating their effects on antioxidant systems to protect the plant from UV-B stress. This article is protected by copyright. All rights reserved.

Keywords: Arabidopsis thaliana; UV radiation; UV-B signaling pathway; abiotic stress; hormones; melatonin.