Exploring the evolution of (1,3;1,4)-β-D-glucans in plant cell walls: comparative genomics can help!

A key distinguishing feature of the grasses is that their cell walls contain (1,3;1,4)-beta-D-glucans, which are distributed almost exclusively within the Poaceae. The identification of genes that mediate in (1,3;1,4)-beta-D-glucan biosynthesis has been possible through relatively recent genome sequencing programmes and comparative genomics techniques. The evolution of a single new gene appears to have been sufficient for the first synthesis of (1,3;1,4)-beta-D-glucans and there is compelling evidence that existing hydrolytic enzymes were adapted for the specific hydrolysis of the polysaccharide during wall turnover or degradation. Manipulation of the expression levels of genes involved in (1,3;1,4)-beta-D-glucan synthesis is likely to provide opportunities to enhance the value of grasses and cereals in commercial applications such as human nutrition and biofuel production.