Integrative multi-scale analysis reveals a candidate melatonin receptor associated with early salinity response...

Melatonin serves as a crucial signaling regulator in plants, playing a vital role in their growth, development, and stress responses. Although receptor-mediated signaling has been well characterized for several plant hormones, the integration of melatonin perception into early stress response networks in temperate cereals remains unclear. Here, we employed an integrative, multi-scale approach combining computational modeling with molecular, physiological, and biochemical analyses to investigate the involvement of a candidate melatonin receptor, HvPMTR1, and its associated heterotrimeric G-protein α-subunit, HvGα1, in barley (Hordeum vulgare L.) during early salinity responses. Structural modeling using molecular docking and ligand-tunneling simulations, and membrane topology predictions, supported HvPMTR1 as a seven-transmembrane protein with features compatible with melatonin interaction. Exogenous melatonin application triggered coordinated upregulation of HvPMTR1 and HvGα1, accompanied by controlled reactive oxygen species (ROS) dynamics, enhanced antioxidant capacity, and modulation of stomatal behavior. Under early salinity stress, this signaling axis was more strongly activated in a salinity-tolerant genotype compared with a sensitive genotype and was associated with improved water status and sustained photosynthetic performance. Multivariate analyses further positioned HvPMTR1 and HvGα1 expression dynamics, alongside endogenous melatonin levels, within a signaling framework associated with stress resilience. Collectively, these findings suggest that putative melatonin perception is integrated into early salinity-responsive signaling networks in barley, highlighting a potential regulatory module coordinating molecular signaling with physiological adaptation in a temperate cereal crop.