A single gene boosts tree growth by strengthening wood from the inside out
image: Schematic model of PagKNAT5a-mediated xylem cell elongation and secondary cell wall formation. PagKNAT5a enhances longitudinal cell elongation in vascular tissues by modulating auxin accumulation. Furthermore, its physical interaction with MYB46 synergistically upregulates key genes involved in the lignin biosynthesis pathway.
Credit: Horticulture Research
Understanding how plants coordinate vertical growth with wood formation is essential for improving biomass production. A recent study identifies a regulatory mechanism that links vascular cell elongation with secondary cell wall strengthening during stem development. By activating both hormone-related pathways and lignin biosynthesis, the mechanism promotes taller plants with thicker, mechanically reinforced stems. The research shows that enhanced elongation of xylem vessels and fibers occurs alongside increased deposition of lignin-rich secondary walls, allowing longitudinal and radial growth to proceed in a coordinated manner. These findings reveal how growth rate and structural reinforcement can be genetically synchronized, offering new insight into how woody plants optimize both height and strength during development.
Wood formation underpins plant mechanical support, water transport, and biomass accumulation, making it a central target for forestry improvement. Xylem development involves two tightly linked processes: elongation of vascular cells and deposition of thick secondary cell walls rich in lignin. While many transcription factors regulating these processes have been identified, how plants coordinate cell elongation with secondary wall formation remains poorly understood. In particular, the regulatory roles of class II KNOX transcription factors in woody species are still unclear and sometimes contradictory across plant systems. Based on these challenges, there is a need to investigate how specific regulators integrate hormonal signaling with cell wall biosynthesis to control efficient wood development.
Researchers from Zhejiang A&F University report new insights into wood formation in poplar in a study published (DOI: 10.1093/hr/uhaf125) on 7 May 2025 in Horticulture Research. The team investigated the function of a class II KNOX transcription factor, PagKNAT5a, and demonstrated its role in promoting both stem elongation and secondary xylem thickening. Using transgenic poplar plants, the researchers showed that PagKNAT5a enhances vascular growth by modulating auxin accumulation and activating lignin biosynthesis pathways, revealing a coordinated genetic mechanism underlying plant height increase and wood strengthening.
The study combined anatomical, molecular, and physiological analyses to uncover how PagKNAT5a regulates xylem development. Poplar plants overexpressing PagKNAT5a exhibited significantly increased height and stem diameter without changes in internode number, indicating that growth enhancement resulted from internode elongation rather than altered organ patterning. Microscopic observations showed elongated xylem vessels and fiber cells, confirming enhanced longitudinal growth within vascular tissues.
At the molecular level, PagKNAT5a overexpression elevated auxin levels in xylem-associated tissues by upregulating auxin transport genes while suppressing auxin-conjugating enzymes. This hormonal shift activated downstream cell elongation factors, directly linking transcriptional regulation to vascular cell expansion.
In parallel, the study revealed that PagKNAT5a physically interacts with MYB46, a master regulator of secondary cell wall biosynthesis. This interaction strengthened MYB46 binding to secondary wall MYB-responsive elements, leading to increased expression of lignin biosynthetic genes. As a result, fiber cells developed thicker secondary walls with substantially higher lignin content, while cellulose levels remained unchanged. Together, these findings demonstrate that PagKNAT5a synchronizes vertical growth and radial reinforcement by integrating hormone signaling with secondary wall regulation.
“Our findings reveal how a single transcription factor can coordinate two fundamental aspects of wood development—cell elongation and wall thickening,” said the study’s corresponding authors. “By linking auxin-mediated growth with MYB46-driven lignin biosynthesis, PagKNAT5a enables trees to grow taller while maintaining mechanical strength. This coordination is crucial for woody plants, which must balance rapid growth with structural stability. The work provides a clearer framework for understanding how complex transcriptional networks optimize biomass formation.”
The discovery of PagKNAT5a’s dual regulatory role has important implications for forestry and bioenergy crop improvement. By simultaneously enhancing stem elongation and lignin deposition, this regulatory pathway offers a strategy to increase wood yield without compromising structural integrity. Targeting such integrative regulators could enable the development of fast-growing tree varieties suited for timber, carbon sequestration, and renewable biomass production. More broadly, the study highlights how coordinated genetic control of growth and cell wall formation can improve plant performance, providing a foundation for future efforts to optimize woody biomass under changing environmental and industrial demands.
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References
DOI
Original Source URL
https://doi.org/10.1093/hr/uhaf125
Funding information
This work was supported by the National Natural Science Foundation of China (32201582), the Zhejiang Provincial Natural Science Foundation of China (LQ22C160008), the National Key Research and Development Program of China (2021YFD2200205), the Key Scientific and Technological Grant of Zhejiang for Breeding New Agricultural Varieties (2021C02070-1), and the Research Foundation of Zhejiang A&F University (2018FR013).
About Horticulture Research
Horticulture Research is an open access journal of Nanjing Agricultural University and ranked number one in the Horticulture category of the Journal Citation Reports ™ from Clarivate, 2023. The journal is committed to publishing original research articles, reviews, perspectives, comments, correspondence articles and letters to the editor related to all major horticultural plants and disciplines, including biotechnology, breeding, cellular and molecular biology, evolution, genetics, inter-species interactions, physiology, and the origination and domestication of crops.