Abstract:Beta-glucan is a noncellulosic polysaccharide linked by β-(1,3) and β-(1,4) glycosidic bonds, mainly distributed in the endosperm and aleurone layer of cereal crop grains with the synthesis in the Golgi apparatus, transportation to the plasma membrane by vesicles, and deposition in the cell wall. Beta-glucan is effective in reducing cholesterol and blood sugar levels by increasing bile acid excretion and delaying glucose absorption. Members of the β-glucan synthase gene families were firstly identified in rice (Oryza sativa), and subsequently discovered in other cereal crops. There are three main subfamilies (CslF, CslH and CslJ) in β-glucan synthase with the formation via convergent evolution. These three subfamilies originated from different clades and evolved their respective functions independently. During evolution, the purifying selection pressure resulted in the high conservation of sequences for members of β-glucan synthase gene families. CslF subfamily members are relatively large and often form gene clusters on chromosomes, and CslF6 is the key gene mediating β-glucan synthesis. CslF subfamily members showed the relatively high expression levels in young tissues such as leaf bases, and they were affected by light intensity obviously. There are relatively few members in CslH and CslJ subfamilies, CslH genes presented the relatively high expression levels in mature tissues such as leaf tips, while CslJ genes showed the relatively high expression levels in young one like grains. The research progress on the phylogenetic relationships for members of β-glucan synthase gene families, the subcellular localization of β-glucan synthase, and the directional breeding in cereal crops were summarized. The accurate localization of β-glucan synthase genes on chromosomes is prospected for the future research. The review aims to promote the directionally breeding of cereal crops with high β-glucan content by the chromosome engineering.
