Overexpression of PagMYB206 enhances secondary cell wall biosynthesis under low nitrogen availability in poplar.

Nitrogen (N) deficiency is a major limiting factor for the growth and productivity of perennial trees. In woody plants, secondary xylem formation is influenced by N availability, yet the molecular mechanisms underlying the wood property changes under low nitrogen (LN) conditions remain unclear. This study aimed to investigate the role of PagMYB206 in regulating secondary xylem development and acclimation to LN stress in Populus alba × Populus glandulosa. PagMYB206 was predominantly expressed in the secondary xylem and was upregulated in the stems under LN treatment. Overexpression of PagMYB206 improved growth performance, with higher levels of amino acids and total N content compared with WT poplars under LN conditions. Furthermore, PagMYB206-OE poplars exhibited enhanced xylem development under nitrogen deficiency, including wider xylem, thicker double fiber walls, and larger diameters of fiber and vessel lumens, accompanied by increased biosynthesis of lignin, cellulose, and hemicellulose. RT-qPCR analysis revealed that PagMYB206 upregulated genes involved in secondary cell wall biosynthetic and N metabolism pathways in LN-treated wood. Importantly, PagMYB206 directly binds to the promoter region of PagGT43B, a key xylan biosynthesis gene, to activate its expression. Our findings suggest that PagMYB206 coordinates secondary xylem formation and N metabolism, providing new insights into its role in enhancing poplar adaptation to low nitrogen availability.