Secondary cell wall (SCW) formation and lignin biosynthesis are critical biological processes that determine wood properties. Masson pine (Pinus massoniana Lamb) 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 that PmMYB289, a member of the P20 subgroup, is highly homologous to the Arabidopsis SCW regulators AtMYB52 and AtMYB54. Expression profiling demonstrated that PmMYB289 is predominantly expressed in highly lignified old stems. Transcriptional activation assays confirmed that PmMYB289 lacks autoactivation activity. Subcellular localization analysis revealed that PmMYB289 was localized to the nucleus. Ectopic overexpression of PmMYB289 in 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 of NbPAL1. 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.
Li et al. (Thu,) studied this question.