Phytomelatonin and secondary metabolites: Operative strategies to induce plant abiotic stress tolerance

Abiotic stresses, such as salt, drought, heavy metals and extreme temperatures, severely affect plant growth and metabolism, leading to reduced crop productivity. In response to these challenges, plants accelerate the biosynthesis of secondary metabolites (SMs), including polyphenols, flavonoids, terpenoids and glucosinolates, which act as defense molecules to mitigate abiotic stress. Additionally, SMs not only contribute to stress tolerance but also have significant applications in pharmaceuticals, food industries and agriculture. Phytomelatonin (MT), a ubiquitously present indoleamine, has emerged as a key regulator of SMs production to stimulate defense mechanisms. For instance, MT could facilitate polyamines (PAs) accumulation, including putrescine (Put), spermidine (Spd) and spermine (Spm) by 3.1, 3.5, and 2.1 folds, respectively, under waterlogging stress in alfalfa ( Medicago sativa ), suggesting the potential of MT to modulate SMs for improving stress tolerance. However, there is lack of a comprehensive review highlighting the significance of how MT could modulate SMs under abiotic stress. Thus, in the present review, we aimed to discuss the potential of MT to activate SMs production and promote abiotic stress tolerance, along with shedding significance on the future implications of omic(s)-integrated gene editing strategies to generate tolerant crop lines.