No abstract

Cell walls are crucial for the integrity and function of all land plants and are of central importance in human health, livestock production, and as a source of renewable bioenergy. Many enzymes that mediate the biosynthesis of cell wall polysaccharides are encoded by members of the large () gene superfamily. Here, we analyzed 29 sequenced genomes and 17 transcriptomes to revise the phylogeny of the gene superfamily in angiosperms. Our results identify ancestral gene clusters that predate the monocot-eudicot divergence and reveal several novel evolutionary observations, including the expansion of the Poaceae-specific cellulose synthase-like family to the graminids and restiids and the characterization of a previously unreported eudicot lineage, , that forms a reciprocally monophyletic eudicot-monocot grouping with the clade. The lineage is widely distributed in eudicots, and the clade, which was thought previously to be restricted to the Poales, is widely distributed in monocots. Our analyses show that some members of the lineage, but not the newly identified genes, are capable of directing (1,3;1,4)-β-glucan biosynthesis, which, contrary to current dogma, is not restricted to Poaceae.

An ␣-L-arabinofuranosidase and a ␤-D-xylosidase, designated ARA-I and XYL, respectively, have been purified about 1,000-fold from extracts of 5-day-old barley (Hordeum vulgare L.) seedlings using ammonium sulfate fractional precipitation, ion exchange chromatography, chromatofocusing, and size-exclusion chromatography. The ARA-I has an apparent molecular mass of 67 kDa and an isoelectric point of 5.5, and its catalytic efficiency during hydrolysis of 4-nitrophenyl ␣-L-arabinofuranoside is only slightly higher than during hydrolysis of 4-nitrophenyl ␤-D-xyloside. Thus, the enzyme is actually a bifunctional ␣-L-arabinofuranosidase/␤-D-xylosidase. In contrast, the XYL enzyme, which also has an apparent molecular mass of 67 kDa and an isoelectric point of 6.7, preferentially hydrolyzes 4-nitrophenyl ␤-D-xyloside, with a catalytic efficiency ϳ30-fold higher than with 4-nitrophenyl ␣-L-arabinofuranoside. The genes encoding the ARA-I and XYL have been mapped to chromosomes 2H and 6H, respectively. ARA-I transcripts are most abundant in young roots, young leaves, and developing grain, whereas XYL mRNA is detected in most barley tissues.