Abstract

Salt stress induces TaCOMT-associated melatonin production in wheat roots. • LCD-dependent H 2 S production participates in MT-alleviated salt stress. • MT regulates redox and Na + /K + homeostasis via H 2 S signal in salt-stressed roots. Soil salinization represents a significant environmental challenge that adversely affects the growth and productivity of wheat ( Triticum aestivum L.), primarily by impeding root development. Although melatonin (MT) is acknowledged as a crucial phytohormone involved in responses to abiotic stress, the precise mechanisms through which endogenous MT facilitates salt tolerance in wheat roots remain inadequately elucidated. In this study, we observed that salinity stress induces a rapid accumulation of endogenous MT in wheat roots, which is associated with a marked upregulation of the biosynthetic gene TaCOMT . Heterologous overexpression of TaCOMT in Arabidopsis resulted in significantly elevated MT levels and conferred enhanced salt resistance, as evidenced by increased root biomass and length. Mechanistic investigations indicated that MT functions upstream of hydrogen sulfide (H 2 S) signaling. MT treatment prompted a surge in endogenous H 2 S production by enhancing the activity of the biosynthetic enzyme L -cysteine desulfhydrase. Pharmacological interventions revealed that the protective effects of MT, particularly in restoring redox homeostasis and maintaining ion balance, were nullified by the removal of H 2 S. Collectively, these findings suggest a critical role for MT in modulating salt tolerance through H 2 S signaling pathways.