| Summary: | (1,3;1,4)-β-<span style="font-variant: small-caps;">d</span>-Glucans, also named as mixed-linkage glucans, are unbranched non-cellulosic polysaccharides containing both (1,3)- and (1,4)-β-linkages. The linkage ratio varies depending upon species origin and has a significant impact on the physicochemical properties of the (1,3;1,4)-β-<span style="font-variant: small-caps;">d</span>-glucans. (1,3;1,4)-β-<span style="font-variant: small-caps;">d</span>-Glucans were thought to be unique in the grasses family (Poaceae); however, evidence has shown that (1,3;1,4)-β-<span style="font-variant: small-caps;">d</span>-glucans are also synthesized in other taxa, including horsetail fern <i>Equisetum</i>, algae, lichens, and fungi, and more recently, bacteria. The enzyme involved in (1,3;1,4)-β-<span style="font-variant: small-caps;">d</span>-glucan biosynthesis has been well studied in grasses and cereal. However, how this enzyme is able to assemble the two different linkages remains a matter of debate. Additionally, the presence of (1,3;1,4)-β-<span style="font-variant: small-caps;">d</span>-glucan across the species evolutionarily distant from Poaceae but absence in some evolutionarily closely related species suggest that the synthesis is either highly conserved or has arisen twice as a result of convergent evolution. Here, we compare the structure of (1,3;1,4)-β-<span style="font-variant: small-caps;">d</span>-glucans present across various taxonomic groups and provide up-to-date information on how (1,3;1,4)-β-<span style="font-variant: small-caps;">d</span>-glucans are synthesized and their functions.
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