Core Insights - Melatonin in plants plays a dual role as both a growth promoter and a stress inducer, enhancing crop yield under optimal conditions while providing resistance against environmental stressors [2][4] - The discovery of the melatonin receptor PMTR1 has opened new avenues for understanding plant defense signaling and its rapid response mechanisms [4] Group 1: Melatonin's Role in Plants - Melatonin regulates plant growth by promoting root development and leaf expansion through the cytokinin signaling pathway, maximizing yield in suitable environments [2] - Under stress conditions such as drought or salinity, melatonin levels increase, activating heat shock proteins and antioxidant enzyme systems, thereby enhancing plant resilience [2] - For instance, in rice, exogenous application of melatonin can increase root length by 40% and improve photosynthetic efficiency by 35% under saline conditions, challenging the traditional notion that high yield and stress resistance are mutually exclusive [2] Group 2: Melatonin Synthesis Pathway - The synthesis pathway of plant melatonin is complex, involving multiple cellular compartments such as the endoplasmic reticulum, chloroplasts, mitochondria, and cytoplasm, allowing precise regulation of melatonin levels under varying growth conditions [3] - During drought stress, the expression of melatonin synthesis genes in chloroplasts is significantly upregulated, enabling plants to initiate local stress response programs [3] Group 3: PMTR1 Receptor and Defense Mechanisms - The PMTR1 receptor activates intracellular signaling pathways, including reactive oxygen species and calcium ion signaling, triggering a rapid defense response within five minutes of pathogen invasion or extreme temperature exposure [4] - PMTR1 exhibits a dose-dependent regulatory feature, promoting stomatal opening at low melatonin concentrations for optimal photosynthesis, while closing stomata at higher concentrations to mitigate drought stress [4] - The potential application of melatonin in organic agriculture is significant, as it can be precisely regulated through gene editing, leading to the development of "smart crops" and reducing chemical pesticide usage by over 70% [4]