• Secondary growth is a key characteristic of trees, which requires the coordination of multiple regulatory mechanisms including transcriptional regulators and microRNAs (miRNAs). However, the roles of microRNAs in the regulation of secondary growth need to be explored in depth.
• Here, the role of miR319a and its target, PtoTCP20, in the secondary growth of Populus tomentosa stem was investigated using genetic and molecular analyses.
• The expression level of miR319a gradually decreased from primary to secondary growth in P. tomentosa, while that of PtoTCP20 gradually increased. MiR319a overexpression in seedlings resulted in delayed secondary growth and decreased xylem production, while miR319a knockdown and PtoTCP20 overexpression promoted secondary growth and increased xylem production. Further analysis showed that PtoTCP20 interacted with PtoWOX4a and activated PtoWND6 transcription in vitro and in vivo.
• Our data show that PtoTCP20 controls vascular cambium proliferation by binding to PtoWOX4a, and promotes secondary xylem differentiation by activating PtoWND6 transcription, thereby regulating secondary growth in P. tomentosa. Our findings provide insight into the molecular mechanisms underlying secondary growth in trees.

中文翻译：

---

靶向MiR319a的PtoTCP20通过与毛白杨中的PtoWOX4和PtoWND6相互作用来调节次级生长。

• 次生生长是树木的关键特征，它需要协调多种调控机制，包括转录调控因子和microRNA（miRNA）。但是，microRNA在二级生长调控中的作用需要深入探讨。
• 在这里，使用遗传和分子分析研究了miR319a及其靶标PtoTCP20在毛白杨茎的次级生长中的作用。
• miR319a的表达水平从初级逐渐降低至在二次生长毛白杨，而的PtoTCP20逐渐增加。幼苗中的MiR319a过表达导致次级生长延迟和木质部生成减少，而miR319a的敲低和PtoTCP20过表达促进次级生长和木质部生成增加。进一步的分析表明，PtoTCP20相互作用与PtoWOX4a和活化PtoWND6转录体外和体内。
• 我们的数据表明，PtoTCP20通过与PtoWOX4a结合来控制血管形成层的增殖，并通过激活PtoWND6转录促进次生木质部分化，从而调节毛白杨的次生生长。我们的发现提供了对树木次生生长的分子机制的深入了解。