Overexpression of a Xylem-Dominant Expressing BTB Gene, PtrBTB82, Influences Cambial Activity and SCW Synthesis in Populus trichocarpa.

The BTB/POZ protein family is widely distributed across the biological kingdom, and its various subfamilies perform diverse physiological functions, including regulating plant growth and development, defending against pathogen invasion, participating in metabolic regulation, and responding to abiotic stresses. However, the functional roles of BTB genes in wood formation remain largely unknown. In this study, a total of 103 BTB genes were identified in Populus trichocarpa. Expression pattern analysis and β-glucuronidase (GUS) staining revealed that PtrBTB82 was predominantly expressed in the xylem. Overexpression of PtrBTB82 in P. trichocarpa significantly reduced cambial activity, resulted in a narrower xylem, and altered the chemical composition of the secondary cell wall, suggesting that PtrBTB82 plays the roles in wood formation. Quantitative real-time PCR (RT-qPCR) analysis showed that overexpression of PtrBTB82 suppressed the expression of genes related to the WUSCHEL-related pathway and plant hormone signaling, which may underlie the reduced cambial activity and inhibited xylem development. Moreover, genes associated with lignin biosynthesis (PtrPALs, PtrC4H1, Ptr4CL and PtrCAD1) were upregulated, while secondary wall cellulose synthase genes (PtrCESA7A/B and PtrCESA8A) were markedly downregulated in the overexpression lines, likely contributing to the altered chemical composition of the wood. Collectively, this study provides new insights into the role of PtrBTBs in wood formation, thereby revealing the functional diversity of the BTB family in plants.