Abstract
Wood formation is a biological process during which the most abundant lignocellulosic biomass on earth is produced. Although a number of transcription factors have been linked to the regulation of wood formation process, none of them has been demonstrated to be a higher hierarchical regulator that coordinately regulates secondary wall biosynthesis genes. Here, we identified a Populus gene, PsnSHN2, a counterpart of the Arabidopsis AP2/ERF type transcription factor, SHINE2. PsnSHN2 is predominantly expressed in xylem tissues and acted evidently as a high hierarchical transcriptional activator. Overexpression of PsnSHN2 in tobacco significantly altered the expression of both transcription factors and biosynthesis genes involved in secondary wall formation, leading to the thickened secondary walls and the changed cell wall composition. The most significant changes occurred in the contents of cellulose and hemicellulose that increased 37% and 28%, respectively, whereas the content of lignin that decreased 34%. Furthermore, PsnSHN2 activated or repressed the promoter activities of transcription factors involved in secondary wall biosynthesis and bound to five cis-acting elements enriched in the promoter regions of these transcription factors. Taken together, our results suggest PsnSHN2 coordinately regulate secondary wall formation through selective up/down-regulation of its downstream transcription factors that control secondary wall formation.
Highlights
Wood formation is a biological process during which the most abundant lignocellulosic biomass on earth is produced
We isolated the full length cDNA sequence encoding a protein of 179 amino acid residues, which is 100%, 90.3%, and 95.2% identical to the P. trichocarpa putative SHINE protein (27009360), E. grandis SHN2 (32053465) and A. thaliana SHN2 (19673076), respectively
The biosynthesis of secondary wall involves a coordinated expression of secondary wall biosynthesis genes regulated by a cascade of TFs2, 7, 9, 11, 12, 35
Summary
Wood formation is a biological process during which the most abundant lignocellulosic biomass on earth is produced. The best-characterized TFs are, for example, Populus trichocarpa wood-associated NAC domain TFs (PtrWNDs), Eucalyptus grandis WND1 (EgWND1) and Populus deltoids MYB21 (PdMYB21)[5, 6, 16, 17] Such a multilayered regulatory network implicates the existence of some high hierarchical regulators that can be tuned to alter different secondary wall biosynthesis pathways in order to optimize secondary wall composition[2, 3, 7, 9, 11, 12, 20]. Our results indicate that PsnSHN2 is a high hierarchical TF that governs the secondary wall formation, and is more importantly capable of coordinately regulating cellulose, hemicellulose, and lignin biosynthesis pathways
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