Abstract
An important component of barley cell walls, particularly in the endosperm, is (1,3;1,4)-β- glucan, a polymer that has proven health benefits in humans and that influences processability in the brewing industry. Genes of the cellulose synthase-like (Csl) F gene family have been shown to be involved in (1,3;1,4)-β-glucan synthesis but many aspects of the biosynthesis are still unclear. Examination of the sequence assembly of the barley genome has revealed the presence of an additional three HvCslF genes (HvCslF11, HvCslF12 and HvCslF13) which may be involved in (1,3;1,4)-β-glucan synthesis. Transcripts of HvCslF11 and HvCslF12 mRNA were found in roots and young leaves, respectively. Transient expression of these genes in Nicotiana benthamiana resulted in phenotypic changes in the infiltrated leaves, although no authentic (1,3;1,4)-β-glucan was detected. Comparisons of the CslF gene families in cereals revealed evidence of intergenic recombination, gene duplications and translocation events. This significant divergence within the gene family might be related to multiple functions of (1,3;1,4)-β-glucans in the Poaceae. Emerging genomic and global expression data for barley and other cereals is a powerful resource for characterising the evolution and dynamics of complete gene families. In the case of the CslF gene family, the results will contribute to a more thorough understanding of carbohydrate metabolism in grass cell walls.
Highlights
Interest in barley as a food component has been increasing due to the comparatively high levels of mixed linkage (1,3;1,4)-bglucan found in the grain
The CslF family members are named after their homologs in rice, starting with HvCslF3 as there are no homologous sequences in barley to OsCslF1 and OsCslF2
The HvCslF9 gene is located on the short arm of chromosome 1H, HvCslF7 is located on the long arm of chromosome 5H and HvCslF6 is located on the long arm of chromosome 7H (Figure 2)
Summary
Interest in barley as a food component has been increasing due to the comparatively high levels of mixed linkage (1,3;1,4)-bglucan found in the grain. In 2006, the U.S Food and Drug Administration (FDA) approved health-related claims stating that the intake of 3 grams of soluble b-glucan (from oat or barley) per day helps to effectively lower blood total and LDL cholesterol [1,2]. The (1,3;1,4)-b-glucan functions as soluble dietary fibre and has additional health benefits in reducing the risk of cardiovascular disease (CVD), type II diabetes and colorectal cancer [1,2]. In the gastrointestinal tract, (1,3;1,4)-b-glucan is believed to form a gel matrix that increases bile acid excretion and delays glucose absorption into the blood, lowering insulin levels. (1,3;1,4)-b-glucans are classified as antinutrients in animal feed formulations, where they reduce growth rates of monogastric animals [4]
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