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.
HighlightSeed coat mucilage composition and heteroxylan structure varies between different Plantago species and is accompanied by differences in glycosyltransferase family 61 (GT61) copy number and transcript abundance.
As a significant
component of monocot cell walls, (1,3;1,4)-β-glucan
has conclusively been shown to be synthesized by the cellulose synthase-like
F6 protein. In this study, we investigated the synthetic activity
of other members of the barley (Hordeum vulgare) CslF gene family using heterologous expression. As expected,
the majority of the genes encode proteins that are capable of synthesizing
detectable levels of (1,3;1,4)-β-glucan. However, overexpression
of HvCslF3 and HvCslF10 genes resulted
in the synthesis of a novel linear glucoxylan that consists of (1,4)-β-linked
glucose and xylose residues. To demonstrate that this product was
not an aberration of the heterologous system, the characteristic (1,4)-β-linkage
between glucose and xylose was confirmed to be present in wild type
barley tissues known to contain HvCslF3 and HvCslF10 transcripts. This polysaccharide linkage has also
been reported in species of Ulva, a marine green
alga, and has significant implications for defining the specificity
of the cell wall content of many crop species. This finding supports
previous observations that members of a single CSL family may not
possess the same carbohydrate synthetic activity, with the CSLF family
now associated with the formation of not only (1,3)- and (1,4)-β-glucosidic
linkages, but also (1,4)-β-glucosidic and (1,4)-β-xylosidic
linkages.
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