Dual Regulation of Cuticle and Cell Wall Biosynthesis by <scp>BnaC9</scp> . <scp>MYB46</scp> Confers Drought Tolerance in <scp> <i>Brassica napus</i> </scp>

The plant cuticle and cell wall are pivotal extracellular barriers safeguarding crops against drought, yet their coordinated regulation remains poorly understood. Here, we identify BnaC9.MYB46, an R2R3-MYB transcription factor in the polyploid oilseed Brassica napus, as a dual-function regulatory hub that synchronises cuticle reinforcement and secondary cell wall remodelling to enhance drought resilience. Functional analyses reveal that BnaC9.MYB46 directly activates key genes involved in wax and cutin biosynthesis-including BnaA1.MYB106, BnaLACS3/4/9, BnaKCR1/KCR2, BnaC2.KCS19 and BnaA9.CER1-2-while simultaneously repressing the wax inhibitor BnaC9.DEWAX1. These actions lead to thicker cuticles, enhanced deposition of alkane-rich waxes, modest alterations in cutin-like fatty acids, reduced cuticular permeability and improved water retention. Notably, BnaC2.KCS19 and the BnaC9.DEWAX1-BnaA9.CER1-2 module are validated as critical mediators underpinning wax phenotype and drought tolerance. In parallel, BnaC9.MYB46 promotes the expression of secondary cell wall biosynthesis genes (BnaC9.KOR1, BnaC2.IRX8, BnaC1.F5H), enhancing cellulose, hemicellulose and lignin deposition to stabilise vascular integrity under water deficit. By orchestrating both cuticle fortification and cell wall remodelling, BnaC9.MYB46 establishes dual protective barriers that limit water loss and preserve physiological function. This study redefines MYB46 as a central integrator of extracellular barrier formation and highlights BnaC9.MYB46 as a promising molecular target for breeding drought-resilient rapeseed cultivars through coordinated enhancement of cuticle and cell wall properties.