Abstract

Secondary cell wall (SCW) formation and lignin biosynthesis are critical biological processes that determine wood properties. Masson pine (Pinus massonianaLamb) is a fast-growing conifer species with significant economic value for the pulp and paper industry. While R2R3-MYB transcription factors are known as master regulators of SCW biosynthesis, the specific R2R3-MYB members regulating lignin formation in Masson pine remain largely uncharacterized. In this study, we identified 317 R2R3-MYB genes in the Masson pine genome. Phylogenetic analysis revealed thatPmMYB289, a member of the P20 subgroup, is highly homologous to theArabidopsisSCW regulatorsAtMYB52andAtMYB54. Expression profiling demonstrated thatPmMYB289is predominantly expressed in highly lignified old stems. Transcriptional activation assays confirmed thatPmMYB289lacks autoactivation activity. Subcellular localization analysis revealed thatPmMYB289was localized to the nucleus. Ectopic overexpression ofPmMYB289in tobacco (Nicotiana benthamiana) resulted in dwarfed plant growth, reduced stem diameter, and curled leaves. Molecular analysis of these transgenic lines showed a significant downregulation of most key SCW biosynthetic genes, with the exception ofNbPAL1. These findings indicate that PmMYB289 acts as a crucial transcriptional repressor in SCW biosynthesis, providing valuable genetic resources for the molecular breeding of superior Masson pine varieties.