Phytomelatonin as a central molecule in plant disease resistance.

Melatonin is an essential phytohormone in the regulation of many plant processes, including both during plant development and in response to stress. Pathogen infections cause serious damage to plants and reduce agricultural production. Recent studies indicate that melatonin plays important roles in alleviating bacterial, fungal and viral diseases in plants and post-harvest fruits. Herein, we summarize information related to the effects of melatonin on plant disease resistance. Melatonin, reactive oxygen species (ROS) and reactive nitrogen species (RNS) form a complex loop during plant-pathogen interaction to regulate plant disease resistance. Moreover, melatonin also has crosstalk with other phytohormones including salicylic acid (SA), jasmonic acid (JA), auxin, abscisic acid (ABA) which further activates plant defense genes. Melatonin not only plays an important role in plant immunity, but also in alleviating pathogen pathogenicity. We also summarize the known processes by which melatonin mediates pathogen pathogenicity via negatively regulating the expression levels of genes related to cell viability as well as virulence-related genes. The multiple mechanisms underlying melatonin influences on both plant immunity and pathogen pathogenicity support the recognition of the essential nature of melatonin in plant-pathogen interactions, highlighting phytomelatonin as a critical molecule in plant immune responses.