The <scp>MYC2</scp> ‐ <scp>MYB113</scp> module governs <scp>JA</scp> signaling to regulate anthocyanin accumulation and secondary wall thickening under high light in <i>Populus</i>

Summary High‐light stress limits the productivity of perennial trees by inducing photo‐oxidative damage, physiological decline, and growth inhibition. To acclimate to persistent high light, trees accumulate anthocyanins and thicken secondary cell walls, yet the underlying regulatory mechanisms remain elusive. Here, we show that the R2R3‐Myeloblastosis (R2R3‐MYB) transcription factor PtoMYB113 mediates anthocyanin accumulation and secondary wall formation under high‐light stress in Populus tomentosa . PtoMYB113 is expressed at low levels under normal conditions but is strongly induced by high light in both leaves and stems. Overexpression of PtoMYB113 promotes anthocyanin production and secondary wall thickening but suppresses xylem fiber expansion. A yeast one‐hybrid screen identified PtoMYC2a, a core regulator of the jasmonate (JA) signaling pathway, as a direct activator of the PtoMYB113 promoter. Accordingly, loss of PtoMYC2a or PtoMYB113 reduces anthocyanin accumulation, impairs secondary wall thickening, and enhances xylem fiber elongation under high‐light stress. Exogenous JA phenocopies these high‐light responses in a PtoMYC2a ‐ and PtoMYB113 ‐dependent manner. Collectively, our results uncover a JA‐MYC2‐MYB113 module that coordinates anthocyanin production and secondary cell wall remodeling during long‐term high‐light adaptation, offering mechanistic insights into photoprotection in woody plants.