Genome Wide Association Mapping for Arabinoxylan Content in a Collection of Tetraploid Wheats

Abstract

BackgroundArabinoxylans (AXs) are major components of plant cell walls in bread wheat and are important in bread-making and starch extraction. Furthermore, arabinoxylans are components of soluble dietary fibre that has potential health-promoting effects in human nutrition. Despite their high value for human health, few studies have been carried out on the genetics of AX content in durum wheat.ResultsThe genetic variability of AX content was investigated in a set of 104 tetraploid wheat genotypes and regions attributable to AX content were identified through a genome wide association study (GWAS). The amount of arabinoxylan, expressed as percentage (w/w) of the dry weight of the kernel, ranged from 1.8% to 5.5% with a mean value of 4.0%. The GWAS revealed a total of 37 significant marker-trait associations (MTA), identifying 19 quantitative trait loci (QTL) associated with AX content. The highest number of MTAs was identified on chromosome 5A (seven), where three QTL regions were associated with AX content, while the lowest number of MTAs was detected on chromosomes 2B and 4B, where only one MTA identified a single locus. Conservation of synteny between SNP marker sequences and the annotated genes and proteins in Brachypodium distachyon, Oryza sativa and Sorghum bicolor allowed the identification of nine QTL coincident with candidate genes. These included a glycosyl hydrolase GH35, which encodes Gal7 and a glucosyltransferase GT31 on chromosome 1A; a cluster of GT1 genes on chromosome 2B that includes TaUGT1 and cisZog1; a glycosyl hydrolase that encodes a CelC gene on chromosome 3A; Ugt12887 and TaUGT1genes on chromosome 5A; a (1,3)-β-D-glucan synthase (Gsl12 gene) and a glucosyl hydrolase (Cel8 gene) on chromosome 7A.ConclusionsThis study identifies significant MTAs for the AX content in the grain of tetraploid wheat genotypes. We propose that these may be used for molecular breeding of durum wheat varieties with higher soluble fibre content.

Non-Starch Polysaccharides in Durum Wheat: A Review

“…In this case we failed to map the position of the gene on chromosome group 7 in durum. It is noteworthy that associations with isoamylase and (1,4)-β-xylan endohydrolase were reported on chromosome 7A [27].…”

“…The ratio of the (1,4)-to (1,3)-linkages in grain varies between species, from 2.5:1 to 3.4:1 in durum [27], from 2.9:1 to 3.4:1 in barley, from 1.8:1 to 2.3:1 in oats and 2.7:1 in rye [28]. As adjacent (1,3)-linkages are rare or absent, these single (1,3)-linkages are separated by mostly two or three (1,4)-linkages, but also by longer regions of up to 10 (1,4)-linkages [29].…”

“…As mentioned above, the same asymmetry is responsible for the high viscosity of (1,3;1,4)-β-glucan when it is extracted from cereal grains in the alimentary tract of monogastric animals and hence for the beneficial effects on human health and nutrition [33]. The ratio of the (1,4)-to (1,3)-linkages in grain varies between species, from 2.5:1 to 3.4:1 in durum [27], from 2.9:1 to 3.4:1 in barley, from 1.8:1 to 2.3:1 in oats and 2.7:1 in rye [28]. As adjacent (1,3)-linkages are rare or absent, these single (1,3)-linkages are separated by mostly two or three (1,4)linkages, but also by longer regions of up to 10 (1,4)-linkages [29].…”

Identification of a major QTL and associated molecular marker for high arabinoxylan fibre in white wheat flour

“…This identified seven loci involved in WE-AX viscosity: three co-located with the meta-QTL on chromosomes 1B, 3D and 6B and four additional loci on chromosomes 3A, 5B, 7A and 7B. Marcotuli et al [19] reported 19 QTL for AX content in a population of 104 tetraploid wheats.…”

Identification of a major QTL and associated marker for high arabinoxylan fibre in white wheat flour

“…A number of studies of the genetic control of AX content have been reported using genetic analysis, with most analysing wholemeal flour by either direct determination of AX (by monosaccharide analysis or colorimetric determination) or the relative viscosity of aqueous extracts as a proxy (Martinant et al 1998;Perretant et al 2000;Laperche et al 2007;Quraishi et al 2009;Charmet et al 2009;Nyugen et al;Yang et al, 2015), for AX content. In addition, two association studies of AX in wholemeal tetraploid wheat (Marcotuli et al, 2015) and in white flour of bread wheat (Quraishi et al, 2011) have been reported. However, although these studies identified a number of QTL, these were not consistent across crosses and have not led to the identification of markers for breeding.…”