The PagWUS-PagCLV3 module regulates shoot meristem maintenance and activity in poplar

The shoot apical meristem of vascular plants generates all the aboveground organs. During this process, the structure and function of the meristem are maintained by a group of regulatory genes, among which the WUSCHEL (WUS)-CLAVATA3 (CLV3) module plays the core role. To date, all of the insights into shoot meristem homeostasis have been derived from studies on herbaceous plants. The mechanism by which the shoot meristem is maintained in trees remains unknown. In this study, we analyzed the functions of the poplar genes PagWUS and PagCLV3, homologs of Arabidopsis WUS and CLV3, respectively, in the maintenance and regeneration of the shoot meristem. Our results reveal both conserved and divergent functions compared to those of their orthologs in herbaceous species. Similar to their herbaceous counterparts, PagWUS and PagCLV3 are specifically expressed in the organizing center and stem cells, respectively, and form a feedback loop that regulates shoot meristem maintenance. Overexpression of PagWUS promoted shoot regeneration. Compared with herbaceous species, poplar possesses a much larger stem cell niche. The function of the PagWUS-PagCLV3 module is consistent with the developmental characteristics of perennial trees in that it regulates the cessation of the shoot meristem and mediates the proper pattern of secondary growth. Disruption of PagCLV3 enhanced shoot regeneration capacity. Our results shed light on shoot meristem regulation in trees and pave the way for understanding the mechanisms of meristem activity and plant development.