The cysteine2/histidine2-type transcription factor ZINC FINGER OF ARABIDOPSIS THALIANA 6-activated C-REPEAT-BINDING FACTOR pathway is essential for melatonin-mediated freezing stress resistance in Arabidopsis

Melatonin (N-acetyl-5-methoxytryptamine) is not only a widely known animal hormone, but also an important regulator in plant development and multiple abiotic stress responses. Recently, it has been revealed that melatonin alleviated cold stress through mediating several cold-related genes, including C-REPEAT-BINDING FACTORs (CBFs)/Drought Response Element Binding factors (DREBs), COR15a, and three transcription factors (CAMTA1, ZINC FINGER OF ARABIDOPSIS THALIANA 10 (ZAT10), and ZAT12). In this study, we quantified the endogenous melatonin level in Arabidopsis plant leaves and found the endogenous melatonin levels were significantly induced by cold stress (4 degrees C) treatment. In addition, we found one cysteine2/histidine2-type zinc finger transcription factor, ZAT6, was involved in melatonin-mediated freezing stress response in Arabidopsis. Interestingly, exogenous melatonin enhanced freezing stress resistance was largely alleviated in AtZAT6 knockdown plants, but was enhanced in AtZAT6 overexpressing plants. Moreover, the expression levels of AtZAT6 and AtCBFs were commonly upregulated by cold stress (4 degrees C) and exogenous melatonin treatments, and modulation of AtZAT6 expression significantly affected the induction AtCBFs transcripts by cold stress (4 degrees C) and exogenous melatonin treatments. Taken together, AtZAT6-activated CBF pathway might be essential for melatonin-mediated freezing stress response in Arabidopsis.