背景回顾：Activity of the vascular cambium gives rise to secondary xylem for wood formation in trees. The transcription factor WUSCHEL-related HOMEOBOX4 (WOX4) is a central regulator downstream of the hormone and peptide signaling pathways that maintain cambial activity. 

提出问题：However, the genetic regulatory network underlying WOX4-mediated wood formation at the post-transcriptional level remains to be elucidated. 

主要发现：In this study, we identified the ubiquitin receptor PagDA1 in hybrid poplar (Populus alba × P. glandulosa clone 84K) as a negative regulator of wood formation, which restricts cambial activity during secondary growth. 

结果1-DA1过表达和敲除表型：Overexpression of PagDA1 in poplar resulted in a relatively reduced xylem due to decreased cambial cell division. By contrast, mutation of PagDA1 by CRISPR/Cas9 resulted in an increased cambial cell activity and promoted xylem formation. 

结果2-DA1与WOX4：Genetic analysis demonstrated that PagDA1 functions antagonistically in a common pathway as PagWOX4 to regulate cambial activity. We propose that PagDA1 physically associates with PagWOX4 and modulates the degradation of PagWOX4 by the 26S proteasome. Moreover, genetic analysis revealed that PagDA1 exerts its negative effect on cambial development by modulating the stability of PagWOX4 in a ubiquitin-dependent manner mediated by the E3 ubiquitin ligase PagDA2.

结论：In sum, we have identified a cambial regulatory protein complex, PagDA1-PagWOX4, as a potential target for wood biomass improvement.

 摘 要 

林木木材形成过程中的次生木质部主要决定于维管形成层的活性。WOX4是激素和多肽信号转导下游的主要调控子，作用于形成层活性的维持。但是，WOX4介导的木材形成在翻译后水平的遗传调控机制仍不清楚。本文中，作者在84K杨中鉴定到了一个泛素受体PagDA1，该蛋白作为木材形成的负调控子发挥功能，能够在次生生长过程中限制形成层的活性。PagDA1基因在杨树中过表达会导致形成层细胞分裂减少，从而导致木质部减少。相反，通过CRISPR/Cas9敲除PagDA1基因则会导致形成层活性的增强，促进木质部的形成。遗传分析显示，PagDA1与PagWOX4拮抗作用于同一途径，调控形成层活性。作者认为PagDA1能够与PagWOX4发生物理互作，通过26S蛋白酶体促进PagWOX4的降解。此外，遗传分析显示PagDA1还会通过一个由E3泛素连接酶介导的泛素化途径依赖方式，调控PagWOX4蛋白的稳定性。综上，本文的研究揭示了一个作用于形成层活性调控的PagDA1-PagWOX4蛋白复合体，可用于杨树木材生物量的改良。

 周功克