Plant Gene and Trait 2024, Vol.15, No.1, 44-51 http://genbreedpublisher.com/index.php/pgt 47 3.3.2 Impact on glycosyltransferase gene expression Epigenetic modifications can lead to stable and heritable changes in gene expression without altering the DNA sequence. These modifications can either activate or repress GT gene expression, thereby influencing the biosynthesis of cell wall components. For example, histone modifications such as acetylation and methylation can either promote or inhibit the transcription of genes involved in xylan biosynthesis, ultimately affecting wood quality and properties. In summary, the genetic regulation of glycosyltransferases in Populus involves a complex interplay of transcriptional, post-transcriptional, and epigenetic mechanisms. Key transcription factors, regulatory networks, RNA processing, miRNAs, and epigenetic modifications all contribute to the precise control of GT gene expression, which is essential for proper cell wall biosynthesis and wood formation. 4 Impact of Glycosyltransferases on Wood Mechanical Properties 4.1 Xylan's role in wood structure 4.1.1 Contribution to cell wall integrity and strength Xylan is a crucial hemicellulose component in the secondary cell walls of hardwood species, significantly contributing to the structural integrity and mechanical strength of wood. The xylan backbone, synthesized by glycosyltransferases (GTs) such as GT43, GT47, and GT8, plays a pivotal role in maintaining cell wall rigidity and resilience. Downregulation of GT43 genes in hybrid aspen has shown to reduce xylan content, leading to thinner cell walls and altered cellulose orientation, which impacts the overall mechanical properties of the wood (Figure 1) (Ratke et al., 2018). Additionally, the acetylation and glucuronidation of xylan, mediated by specific GTs, influence its interaction with cellulose and lignin, further affecting the wood's structural properties (Pawar et al., 2017; Lyczakowski et al., 2021). Figure 1 Transcript profiling in transgenic hybrid aspen developing wood with reduced GT43 clade B and C expression levels (Adopted from Ratke et al., 2018) Image caption: (a, b) Venn diagrams of up- and downregulated genes, respectively, and analysis of their expression profiles in wood developing tissues using the ASPWOOD database (Sundell et al., 2017). The heatmaps show that the upregulated genes are mostly expressed in the primary-walled developing wood tissues (cambium and radial expansion zone, CA-RE), and only three genes are expressed in maturation zone (M), whereas the downregulated genes are mostly expressed in the secondary wall formation zone (SW), with few genes expressed in the CA-RE or in the phloem and at the annual ring border (PH-AN). The clusters of genes with similar expression profiles are shown beside the heatmaps, and genes associated with these clusters that are discussed in the text are listed. PCD, programmed cell death; TW, tension wood (Adopted from Ratke et al., 2018)
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