Melatonin and sugar signaling in relation to salt and drought stress tolerance in plants

Plants encounter various environmental challenges like drought and salinity, which disrupt their physiological and biochemical functions and adversely impact growth, development, and overall plant productivity. To counter these challenges, plants deploy various strategies, including modulation of plant growth regulators (PGR), which play a vital role in impacting plant performance under optimum and/or stress conditions. Melatonin (MT), a PGR is known to perform multifaceted functions in plants throughout their lifecycle, from seed germination to fruit development, and it has become recognized as a major factor in enhancing tolerance to abiotic stresses. Though various mechanisms have already been explored for MT action, in this review, we have focused on the role of MT in modulating sugar metabolism, sensing, and their transporters to improve stress adaptation. MT regulates sucrose mobilization via sucrose synthase and invertase activities, upregulates hexose transporters (STP, sugar transportor family), SWEET (sugars will eventually be exported transporters) and SUT (sucrose transporters) for efficient carbohydrate allocation and integration with SnRK1/ABA (sucrose non-frmenting 1-related kinase/Abscisic acid) pathways to sustain photosynthesis, and prime reactive oxyggen species (ROS) scavenging. Sugar signaling through sugar transporters enables efficient sugar allocation and accumulation, serving as osmoprotectants, enhancing antioxidant defenses, and modulating stress-responsive gene expression. Future omics-driven dissection of MT-sugar networks, coupled with CRISPR validation and field applications, promises resilient crop varieties for saline and arid environments.