Fiber-specific expression of <i>PdCel9A6</i> modifies the characteristics of wood fibers in <i>Populus</i>

Wood fiber has been extensively used in the pulp and papermaking industries. The length of fiber cells is critical in determining the quality of paper. In our previous studies, we identified PdCel9A6, a gene encoding endo-1,4-β-glucanases expressed in the developing xylem to affect cell wall formation. In this study, we modified the PdCel9A6 expression specifically in xylem fiber cells. The results showed that the fiber-specific upregulation of PdCel9A6 resulted in increased plant height and internode length. The transgenics significantly increased the fiber cell length in the wood xylem. In wood cell wall components, the transgenics showed a reduction of lignin while increasing cellulose. Furthermore, the characteristics of the paper processed from the transgenics showed a significant improvement in paper strength. Transcriptome studies showed that upregulation of PdCel9A6 in fiber cells leads to changes in transcription related to cell wall remodeling and thickening during xylem development. Together, the study demonstrated a new strategy of fiber cell wall modification that could have the potential to improve forest trees for better pulping and papermaking.