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The PagGRF20–PagMYB4 regulatory module coordinates wood formation in poplar

Tong Wang1,2,3†, Haofei Wang1,2,3†, Jingna Si1,2,3†, Jiadong Wu1,2,3, Chen Zhang4,5, Sen Yang1,2,3, Xuefei Cao5, Xiang Zhang1,2,3, Yan Li6,7, Yousry A. El-Kassaby8, Lin Liu1,2,3, Deqiang Zhang1,2,3, Zhong Chen9* and Jianbo Xie1,2,3*   

  1. 1. State Key Laboratory of Tree Genetics and Breeding, College of Biological Sciences and Technology, Beijing Forestry University, Beijing 100083, China
    2. National Engineering Research Center of Tree Breeding and Ecological Restoration, Beijing Forestry University, Beijing 100083, China
    3. The Tree and Ornamental Plant Breeding and Biotechnology Laboratory of National Forestry and Grassland Administration, Beijing Forestry University, Beijing 100083, China
    4. College of Agricultural Engineering and Food Science, Shandong University of Technology, Zibo 255049, China
    5. Beijing Key Laboratory of Lignocellulosic Chemistry, Beijing Forestry University, Beijing 100083, China
    6. Research Institute of Forestry, Chinese Academy of Forestry, Beijing 100091, China
    7. Chinese Society of Forestry, Beijing 100091, China
    8. Department of Forest and Conservation Sciences, Faculty of Forestry, The University of British Columbia, Vancouver, BC V6T 1Z4, Canada
    9. State Key Laboratory for Efficient Production of Forest Resources, College of Forestry, Beijing Forestry University, Beijing 100083, China
    †These authors contributed equally to this work.
    *Correspondences: Jianbo Xie (jbxie@bjfu.edu.cn, Dr. Xie is fully responsible for the distribution of all materials associated with this article); Zhong Chen (zhongchen@bjfu.edu.cn)
  • Received:2025-03-18 Accepted:2026-01-14 Online:2026-02-09
  • Supported by:
    This work was supported by funding from the Fundamental Research Funds for the National Key R&D Program of China (nos. 2023YFD2200203), the Project of the National Natural Science Foundation of China (nos. 32371906 and 32022057), Forestry and Grassland Science and Technology Innovation Youth Top Talent Project of China (no. 2020132607), and The Fundamental Research Funds for the Central Universities [QNTD202305, BFUKF202413].

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Abstract: Despite decades of research on NAC–MYB master regulators, the transcription factor (TF)-mediated network governing wood development remains fragmented, hindering a systems-level understanding of secondary xylem formation. In this study, we identified GROWTH REGULATING FACTOR 20 (PagGRF20) as a key regulator within the poplar wood formation network. Compared to wild-type (WT) poplars, the PagGRF20-overexpressing lines showed a 22.1%–23.9% increase in secondary xylem thickness, a 37.7%–43.3% increase in cell wall thickness, and higher cellulose and xylan content. These phenotypic changes coincided with upregulation of genes involved in cellulose and xylan biosynthetic pathways. Conversely, PagGRF20-RNAi lines displayed opposite phenotypic traits. Molecular analyses revealed that PagGRF20 binds to the TGT[C/T]AGA cis-regulatory elements in the promoters of wood polymer biosynthesis genes, modulating polysaccharide production by activating the glycosyltransferase IRREGULAR XYLEM 14-LIKE (PagIRX14L). Crucially, overexpression of PagIRX14L in poplar increased the xylan content and decreased lignin levels, suggesting that PagGRF20-mediated transcriptional activation of PagIRX14L significantly contributes to the observed shifts in cell wall composition. Additionally, the R2R3–MYB repressor PagMYB4 physically interacts with PagGRF20, forming a transcriptional complex that suppresses lignin biosynthesis genes, including LACCASE 11 (PagLAC11), potentially altering the balance of cell wall components and affecting cellulose and xylan accumulation. Finally, we built a three-layer, PagGRF20-centered regulatory network to uncover the mechanisms and target genes underlying wood formation. Our results suggest that the PagGRF20–PagMYB4 module coordinates secondary cell wall (SCW) biosynthetic pathways, providing novel insights into engineering wood with enhanced polysaccharide deposition and low lignin content.

Key words: lignin, poplar, secondary xylem, transcription factors, wood formation, xylose

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