Exogenous Melatonin Regulates Hormone Signalling and Photosynthesis‐Related Genes to Enhance <i>Brassica napus.</i> Yield: A Transcriptomic Perspective

Melatonin, a multifunctional signalling molecule in plants, has been increasingly recognized for its role in improving stress tolerance, regulating hormone signalling, and enhancing crop productivity. Exogenous melatonin application represents a promising strategy to enhance crop productivity under global agricultural challenges. This study aimed to investigate the physiological and molecular mechanisms by which melatonin improves yield in Brassica napus. under optimal conditions. Two-week old plants were treated with 10 μM melatonin for 7 days and phenotype was observed. The plants exhibited significant increases in plant height, leaf number, pods per plant, seeds per pod, and 100-seed weight compared to controls. Transcriptomic analysis revealed 2924 differentially expressed genes (DEGs; 1655 upregulated, 1269 downregulated) from 66 258 genes in response to exogenously applied melatonin. Functional enrichment highlighted profound upregulation of photosynthesis-related pathways, including photosystem I/II components (PsbO, PsaH), electron transport genes (PetE, PetH), and F-type ATPase subunits. Melatonin also reconfigured phytohormone signaling, upregulating auxin (AUX1; BnaA10g27610D), ABA (ABF; BnaA06g04750D), cytokinin (CRF1; BnaA06g34500D, A-ARR; BnaC03g48210D, Bna08g14280D, Bna09g36380D, BnaCnng49490D, BnaA06g16900D, and BnaA06g06240D), and gibberellin-associated genes while downregulating ABA repressors (PYR/PYL; BnaA06g40360D, BnaC07g19450, PP2C; BnaA06g23040D, and BnaA01g37370D). Transcription factor profiling showed activation of growth-promoting families (NAC, TCP, bHLH) and suppression of stress-responsive TFs (MYB, AP2/ERF, WRKY). Validation via RT-qPCR confirmed RNA-seq reliability (R² = 0.96). Our study demonstrated that low-dose melatonin enhances B. napus yield by coordinately boost photosynthetic efficiency, optimizing hormone signaling, and activating growth-promoting transcription factors to prioritize reproductive development.