Unique Regulatory Mechanism of Melatonin-Mediated Defense Against Vanadium Toxicity in Brassica napus L.

Brassica napus L. (B. napus) is a well-known edible oil crop globally. Its production has been severely damaged by abiotic stresses, including heavy metals. Vanadium (V) is a heavy metal that can cause a reduction in plant biomass, photosynthetic pigments, and alleviate ROS production. Melatonin (MT) is a newly emerged nontoxic, regulatory bio-molecule that regulates plant growth against abiotic stresses, but there is limited knowledge about MT's mitigative role against V-induced phytotoxicity in B. napus. The present study investigates the MT based tolerance in B. napus against V toxicity by contructioing gene regulatory network by Weighted gene co-expression network analysis (WGCNA). Transcriptome profiling identified 1767 differentially expressed genes (DEGs) uniquely or commonly regulated in CK, MT, V, and MTV groups. Transcriptome-wide reprogramming at the molecular level showed that MT reduced excessive DEG fluctuations brought on by V stress, bringing expression patterns closer to the control. Cluster analyses (C2, C6) show MT-specific activation of genes involved in phenylpropanoid biosynthesis, jasmonic acid metabolism, and protein folding. WGCNA identified the black and tan modules as strongly correlated with photosynthesis, biomass, and stress traits, pinpointing hub genes NAC072, MYB122, WRKY33, PER72, GSTU19, CYP82G1, ELF5A-2, Cox19-like, RCI2A, GRXC2, MKP1, PNSL2, CYP73A5, thioredoxin H-type, FKBP65, APR3, VHA-c5, and PIG-F as central regulators of stress tolerance. These hub genes converge on redox regulation, secondary metabolism, detoxification, and hormone signaling emerging as an essential pathway. These findings advance our understanding of the mechanisms by which melatonin (MT) alleviates vanadium (V)-induced toxicity and highlight its potential as a promising approach for enhancing heavy metal stress tolerance in B. napus.