Melatonin (N-acetyl-5-methoxytryptamine), produced in the pineal gland which is outside of the blood–brain barrier, acts as an endocrine hormone since it is released into the blood. Melatonin has been studied as a potential treatment of gastroesophageal reflux disease, cancer, immune disorders, cardiovascular diseases, depression, seasonal affective disorder (SAD), circadian rhythm sleep disorders, sexual dysfunction and insomnia in the elderly. Prolonged release melatonin has shown good results in treating insomnia in older adults. It may improve circadian misalignment and SAD. Basic research indicates that melatonin may play a role in modulating the effects of drugs of abuse such as cocaine. Melatonin is also a geroprotector.  

Melatonin 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 and three transcription factors. However, the endogenous melatonin concentration in response to cold stress in was largely unknown, and molecular mechanism of melatonin-mediated plant cold stress responses remains unclear. 

Dr. SHI Haitao, led by Prof. CHAN Zhulong from Wuhan Botanical Garden, quantified the endogenous melatonin level in Arabidopsis plant leaves, and found the endogenous melatonin levels were significantly induced by cold stress (4°C) treatment. In addition, they 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 up-regulated by cold stress (4°C) and exogenous melatonin treatments, and modulation of AtZAT6 expression significantly affected the induction AtCBFs transcripts by cold stress (4°C) and exogenous melatonin treatments.  

Taken together, the results indicated that AtZAT6-activated CBF pathway was essential for melatonin-mediated freezing stress response in Arabidopsis.    

Relevant results were published in Journal of Pineal Research (doi: 10.1111/jpi.12155, IF=7.304) entitled “The Cysteine2/Histidine2-type transcription factorZINC FINGER OF ARABIDOPSIS THALIANA6-activated C-REPEAT-BINDING FACTORpathway is essential for melatonin-mediated freezing stress resistance inArabidopsis”.