TCP23-WRKY15 module negatively regulates lignin deposition and xylem development of wood formation in Populus

Secondary wall, a critical component of wood, is influenced by multiple factors during its formation. The TCP family encodes plant-specific transcription factors (TFs) that play key roles in multiple aspects of plant development. In this study, we identified all TCP TFs in five poplar species and analyzed their evolutionary relationships, gene structures, tissue-specific expression patterns, and potential interactions with microRNAs. Additionally, we screened for TCP proteins associated with secondary wall development that are independent of miRNA regulation. Three candidate TFs were identified, with TCP23 showing high conservation across poplar species and the highest expression levels in the xylem of Populus trichocarpa and Populus wilsonii. The overexpression of TCP23 in poplar inhibited the expression of MYB TFs and structural genes involved in xylem biosynthesis, thereby reducing the lignin content within the stems. By contrast, CRISPR/Cas9-mediated knockout of TCP23 resulted in the opposite effect. Furthermore, we successfully identified WRKY15 as an interaction partner of TCP23 via a yeast two-hybrid library and demonstrated that TCP23 negatively regulates lignin synthesis and xylem development by enhancing the inhibitory function of WRKY15. Our study provides new insights into the transcriptional regulatory mechanisms underlying secondary wall formation.