Haroon Rasheed

Secondary growth is a key process in the growth and development of woody plants, influencing biomass accumulation and structural integrity. The WUSCHEL- related homeobox 4 ( BpWOX4 ) gene regulates vascular cambium activity in trees; however, its precise role in secondary growth in Betula platyphylla remains poorly understood. In this study, we functionally characterized BpWOX4 and its role in secondary growth through a combination of transcriptomic, physiological, and histological analyses. Transcriptome analysis among wild-type (WT), overexpression (O), and suppression (SE) lines revealed upregulation of lignin biosynthesis genes, such as PAL , 4CL , CCR , and CAD . Gene Ontology (GO) and KEGG enrichment analyses indicated activation of the phenylpropanoid and lignin biosynthesis pathways. Additionally, key transcription factors involved in secondary growth, including members of the MYB and NAC families, were significantly upregulated in overexpression lines. Furthermore, overexpression of BpWOX4 in B. platyphylla resulted in increased stem diameter and xylem thickness, as well as significantly higher lignin content. Together, these results provide new insights into the molecular mechanisms underlying secondary growth and identify BpWOX4 as a promising genetic target for enhancing biomass production and wood quality in forest trees.

The adaptation of plants to land requires sophisticated biological processes and signaling. Transcription factors (TFs) regulate several cellular and metabolic activities, as well as signaling pathways in plants during stress and growth and development. The WUSCHEL-RELATED HOMEOBOX (WOX) genes are TFs that are part of the homeodomain (HD) family, which is important for the maintenance of apical meristem, stem cell niche, and other cellular processes. The WOX gene family is divided into three clades: ancient, intermediate, and modern (WUS) based on historical evolution linkage. The number of WOX genes in the plant body increases as plants grow more complex and varies in different species. Numerous research studies have discovered that the WOX gene family play a role in the whole plant’s growth and development, such as in the stem, embryo, root, flower, and leaf. This review comprehensively analyzes roles of the WOX gene family across various plant species, highlighting the evolutionary significance and potential biotechnological applications in stress resistance and crop improvement.