Downregulating aspen xylan biosynthetic <scp>GT</scp>43 genes in developing wood stimulates growth via reprograming of the transcriptome

Abstract

Summary Xylan is one of the main compounds determining wood properties in hardwood species. The xylan backbone is thought to be synthesized by a synthase complex comprising two members of the GT 43 family. We downregulated all GT 43 genes in hybrid aspen ( Populus tremula × tremuloides ) to understand their involvement in xylan biosynthesis. All three clades of the GT 43 family were targeted for downregulation using RNA interference individually or in different combinations, either constitutively or specifically in developing wood. Simultaneous downregulation in developing wood of the B ( IRX 9) and C ( IRX 14) clades resulted in reduced xylan Xyl content relative to reducing end sequence, supporting their role in xylan backbone biosynthesis. This was accompanied by a higher lignocellulose saccharification efficiency. Unexpectedly, GT 43 suppression in developing wood led to an overall growth stimulation, xylem cell wall thinning and a shift in cellulose orientation. Transcriptome profiling of these transgenic lines indicated that cell cycling was stimulated and secondary wall biosynthesis was repressed. We suggest that the reduced xylan elongation is sensed by the cell wall integrity surveying mechanism in developing wood. Our results show that wood‐specific suppression of xylan‐biosynthetic GT 43 genes activates signaling responses, leading to increased growth and improved lignocellulose saccharification.