Melatonin modulates antioxidant-hormonal pathways to improve drought tolerance in cotton

Abstract

Drought stress limits cotton growth and yield. Although exogenous melatonin (MT) can improve drought tolerance, the underlying mechanisms are still unclear. Optimal MT concentrations (100 µM for seed germination and 200 µM for seedlings) were identified in the cotton cultivar Zhong H177 under polyethylene glycol (PEG)-simulated drought. Physiologically, MT treatment was associated with reduced oxidative damage, alongside increased antioxidant enzyme activities and proline (PRO) accumulation, as well as decreased reactive oxygen species (ROS) and malondialdehyde (MDA) levels. Transcriptomic analysis revealed 2992 MT-associated genes involved in redox regulation, hormone signaling, and secondary metabolism. Among these, the gibberellin synthesis gene GHCYP88A1 (GH_A08G1842) showed marked upregulation under drought stress in response to MT treatment. Silencing this gene attenuated the protective effect of MT. Collectively, these findings indicate that MT may enhance drought tolerance, potentially through the coordination of antioxidant activation, hormone network modulation, and gibberellin promotion. This molecular framework provides candidate targets for breeding drought-resistant cotton and potentially other crops.