Plant Gene and Trait 2024, Vol.15, No.1, 44-51 http://genbreedpublisher.com/index.php/pgt 46 xylan biosynthesis with other aspects of plant development (Biswal et al., 2015). Additionally, the expression of GT8 genes is influenced by various environmental and developmental cues, ensuring that xylan modification is coordinated with the overall needs of the plant. 3 Genetic Regulation of Glycosyltransferases 3.1 Transcriptional control 3.1.1 Key transcription factors involved in glycosyltransferase gene expression Transcription factors (TFs) play a crucial role in regulating glycosyltransferase (GT) gene expression. In Populus, several TFs have been identified that influence the expression of genes involved in secondary cell wall biosynthesis, including those encoding GTs. For instance, the R2R3 MYB transcription factor MYB189 has been shown to negatively regulate the biosynthesis of lignin, cellulose, and hemicelluloses by directly binding to the promoters of secondary wall biosynthetic genes, thereby repressing their expression (Jiao et al., 2019). Similarly, PtoMYB156, another R2R3-MYB transcription factor, represses phenylpropanoid biosynthetic genes and secondary wall biosynthetic genes, leading to reduced secondary wall thickness and decreased cellulose, lignin, and xylose content (Yang et al., 2017). Additionally, PdMYB221, a poplar ortholog of the Arabidopsis R2R3-MYB transcription factor AtMYB4, directly regulates secondary wall biosynthesis by repressing the expression of key genes involved in the synthesis of cellulose, xylan, and lignin (Tang et al., 2015). 3.1.2 Regulatory networks influencing GTgene expression The regulatory networks influencing GT gene expression are complex and involve multiple layers of control. For example, the transcription factors PtNST1 and PtMYB21 have been shown to activate the expression of RWA-A and RWA-B genes, which are involved in xylan acetylation in developing wood (Pawar et al., 2017). These regulatory networks ensure the coordinated expression of genes necessary for proper cell wall formation and modification. Furthermore, systems genetics analysis in Eucalyptus has revealed that xylan modification genes are part of expression modules that are co-regulated with genes involved in nucleotide sugar interconversion and phenylalanine biosynthesis, highlighting the interconnected nature of these pathways (Wierzbicki et al., 2019). 3.2 Post-transcriptional regulation 3.2.1 RNA processing and stability Post-transcriptional regulation, including RNA processing and stability, plays a significant role in the regulation of GT genes. RNA interference (RNAi) has been used to downregulate specific GT genes in Populus, leading to changes in xylan biosynthesis and wood properties. For instance, downregulation of GAUT12.1 in Populus deltoides resulted in reduced xylan and pectin content, increased sugar release, and enhanced growth (Biswal et al., 2015). This indicates that RNA processing mechanisms can be targeted to modulate GT gene expression and influence wood quality. 3.2.2 Role of microRNAs in regulating glycosyltransferase genes MicroRNAs (miRNAs) are small non-coding RNAs that regulate gene expression post-transcriptionally by targeting mRNAs for degradation or translational repression. In Populus, miRNAs have been implicated in the regulation of lignin biosynthesis, which is closely linked to GT activity. For example, a study identified 36 miRNA genes associated with lignin biosynthesis, suggesting their potential role in regulating genes involved in cell wall formation, including GTs (Quan et al., 2018). These miRNAs form part of a broader genetic network that coordinates the expression of genes necessary for wood formation. 3.3 Epigenetic regulation 3.3.1 DNA methylation and histone modification Epigenetic regulation, including DNA methylation and histone modification, can significantly impact GT gene expression. Although specific studies on the epigenetic regulation of GT genes in Populus are limited, it is well-established that these mechanisms play a crucial role in gene expression regulation in plants. DNA methylation and histone modifications can alter chromatin structure, thereby influencing the accessibility of transcription factors to GTgene promoters and affecting their transcriptional activity.
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