Meta-analysis of the effect of melatonin application on abiotic stress tolerance in plants

Melatonin is a hormone-like substance that promotes plant growth and development and alleviates stress levels. Although the physiological roles of melatonin and the underlying mechanisms have been qualitatively reviewed in plants, we do not fully understand when and how to apply melatonin to maximize its benefits. Here, we performed a meta-analysis to quantitatively evaluate the effect of melatonin on abiotic stress tolerance in plants and to determine the number of parameters modulated by melatonin. Melatonin significantly alleviated the growth inhibition induced by drought stress compared with other abiotic stresses, including salt, cold, heat, nitrogen deficit, and heavy metal toxicity, mainly owing to higher photosynthesis efficiency and antioxidant enzyme activity. Furthermore, melatonin modulated plant growth in a concentration-dependent manner and was more effective when applied to plants under moderate drought stress at an early stage via root irrigation. In addition, the impact of melatonin was greater in monocots than in dicots. Moreover, endogenous melatonin levels could be significantly increased via transgenic strategies. Among melatonin biosynthesis-related gene members, ASMT has tended to have the most influence on melatonin content in plants. In light of the rapidly developing genome editing technology, quantitatively increasing endogenous melatonin level in plant would be quite useful for moderating climatic conditions and combating desertification. Taken together, our results provide guidelines for melatonin application in crops plants for improving productivity under ongoing climate change.