Melatonin as a regulatory hub of plant hormone levels and action in stress situations

Abstract

Melatonin, a molecule first discovered in animal tissues, plays an important role in multiple physiological responses as a possible plant master regulator. It mediates responses to different types of stress, both biotic and abiotic. Melatonin reduces the negative effects associated with stressors, improving the plant response by increasing plant stress tolerance. When plants respond to stress situations, they use up a large amount of plant resources through a set of perfectly synchronized actions. Responses mediated by melatonin use the plant's hormones to, after adequate modulation, counteract and overcome the negative action of the stressor. In this paper, we review melatonin-plant hormone relationships. Factors that trigger the stress response and the central role of melatonin are analysed. An extensive analysis of current studies shows that melatonin modulates the metabolism of plant hormones (biosynthesis and catabolism), the rise or fall in their endogenous levels, the regulation of signalling elements and how melatonin affects the final response of auxin, gibberellins, cytokinins, abscisic acid, ethylene, salicylic acid, jasmonates, brassinosteroids, polyamines and strigolactones. Lastly, a general overview of melatonin's actions and its regulatory role at a global level is provided and proposals for future research are made.

The Crosstalk of Melatonin and Hydrogen Sulfide Determines Photosynthetic Performance by Regulation of Carbohydrate Metabolism in Wheat under Heat Stress

“…Reports suggest that melatonin mediates several enzymes expression that detoxify excess H2O2 such as, CAT, glutathione/ascorbate reductases, peroxidases in addition to peroxiredoxins [17,79] and balances the ROS/RNS level through antioxidant action. Either endogenous or exogenous supplied melatonin induces its own synthesis presenting melatonin as specific regulator, an anti-stress manager and a plant master regulator [80,81]. Siddiqui et al [82] reported that melatonin induces photosynthetic enzymes, antioxidative system, proline metabolism and carbohydrate level under salt stress.…”

Melatonin as a plant biostimulant in crops and during post‐harvest: a new approach is needed

“…It also plays a role in tissue growth and root generation, amongst others. 7,9,10,23,24 However, melatonin mainly induces the expression of RbOHs (respiratory burst oxidase homolog: plant NADPH-dependent oxidases), which generate superoxide anion, as well as the expression of superoxide dismutases (SOD), which leads to an increase in H 2 O 2 levels. 25 Melatonin induces the expression of several antioxidative enzymes such as catalases, peroxidases and peroxiredoxins, and also many elements of the ascorbate/glutathione cycle, with all them being involved in the control of excess ROS/RNS.…”

“…28 Generally, stressors induce an increase in endogenous melatonin levels in plants through the up-regulation of melatonin biosynthesis enzymes. 24 Lastly, the expression of a large number of enzymes related to plant hormone homeostasis is regulated by melatonin. The expression of genes that encode enzymes of the biosynthetic/catabolic pathways of plant hormones, such as indole-3-acetic acid (auxin), gibberellins, cytokinins, abscisic acid (ABA), ethylene, polyamines, salicylic acid, jasmonic acid (JA) and brassinosteroids, can be up-or down-regulated by melatonin in different situations.…”

“…In many cases, melatonin regulates the expression of several plant hormone receptors and signaling elements. 8,23,24 Figure 1 shows a diagram of the studied beneficial effects of melatonin in plants at different levels.…”

Regulatory hubs in plant stress adaptation

“…Melatonin serves as a master regulator in plants due to its diversity of actions as a mediator between environmental factors, plant hormones and physiological responses. In this Special Issue, Arnao & Hern andez-Ruiz (2021) propose that melatonin acts as a regulatory hub of plant hormone levels and has an important role in stress situations. They outlined melatonin-mediated actions on phytohormones (auxins, GAs, CKs, ABA, ET, SA, JA, BR, PAs and strigolactones) in relation to its biosynthesis, catabolism, signalling elements and final responses.…”