Carbohydrate-active enzymes involved in the secondary cell wall biogenesis in hybrid aspen

Abstract

Wood formation is a fundamental biological process with significant economic interest. While lignin biosynthesis is currently relatively well understood, the pathways leading to the synthesis of the key structural carbohydrates in wood fibers remain obscure. We have used a functional genomics approach to identify enzymes involved in carbohydrate biosynthesis and remodeling during xylem development in the hybrid aspen Populus tremula x tremuloides. Microarrays containing cDNA clones from different tissue-specific libraries were hybridized with probes obtained from narrow tissue sections prepared by cryosectioning of the developing xylem. Bioinformatic analyses using the sensitive tools developed for carbohydrate-active enzymes allowed the identification of 25 xylem-specific glycosyltransferases belonging to the Carbohydrate-Active EnZYme families GT2, GT8, GT14, GT31, GT43, GT47, and GT61 and nine glycosidases (or transglycosidases) belonging to the Carbohydrate-Active EnZYme families GH9, GH10, GH16, GH17, GH19, GH28, GH35, and GH51. While no genes encoding either polysaccharide lyases or carbohydrate esterases were found among the secondary wall-specific genes, one putative O-acetyltransferase was identified. These wood-specific enzyme genes constitute a valuable resource for future development of engineered fibers with improved performance in different applications.

Figure 1.

Clustering using self-organizing maps of 450 genes. Genes with less than two valid data points in sections C to E or with a signal less than 2-fold higher in D than in A to C and E were filtered out.

Figure 2.

Phylogenetic analysis of plant GTs from family GT8. Profile-aligned Populus sequences are in bold, and partial sequences are indicated. Subfamilies with at least one characterized enzyme are outlined by a thick black line and those without defined activities by a thin gray line.

Figure 3.

Phylogenetic analysis of plant GTs from family GT43. Legend as in Figure 2.

Figure 4.

Phylogenetic analysis of plant GTs from family GT47. Legend as in Figure 2.

Figure 5.

Phylogenetic analysis of plant GTs from family GT61. Legend as in Figure 2.