Melatonin's Role in Enhancing Waterlogging Tolerance in Plants: Current Understanding and Future Directions

Waterlogging, increasingly intensified by climate change, limits oxygen availability in the root zone, disrupting carbon and sugar metabolism, leading to energy deficits and oxidative stress that ultimately impair plant growth and productivity. Melatonin, a versatile signaling molecule, mitigates waterlogging-induced stress by enhancing anaerobic respiration and fermentation under oxygen-deprived conditions, upregulating stress-responsive genes, and restoring energy balance through optimized sugar metabolism. It also reduces oxidative damage by strengthening the antioxidant defense system and further improves stress tolerance by modulating phytohormone signaling and influencing rhizosphere microbiome dynamics. However, while melatonin's role in other abiotic stresses is well documented, its molecular mechanisms in conferring waterlogging tolerance, particularly the regulation of transcriptional and epigenetic processes and plant-microbe interaction, remain underexplored. This review synthesizes current knowledge on melatonin's protective mechanisms against waterlogging stress, uniquely integrating insights across physiological, molecular, and ecological dimensions. It addresses a critical research gap by highlighting the underexplored interplay between melatonin and waterlogging-specific responses, offering a novel perspective on its multifaceted roles in plant adaptation. Future research should prioritize elucidating melatonin's influence on transcriptional regulation, epigenetic reprogramming, and plant-microbiome interactions under waterlogged conditions. Moreover, translating these insights into practical, melatonin-based agricultural strategies is essential for developing waterlogging-resilient crops and promoting sustainable farming systems in vulnerable regions.