Identification of a major QTL controlling the content of B-type starch granules in Aegilops

Abstract

Starch within the endosperm of most species of the Triticeae has a unique bimodal granule morphology comprising large lenticular A-type granules and smaller near-spherical B-type granules. However, a few wild wheat species (Aegilops) are known to lack B-granules. Ae. peregrina and a synthetic tetraploid Aegilops with the same genome composition (SU) were found to differ in B-granule number. The synthetic tetraploid had normal A- and B-type starch granules whilst Ae. peregrina had only A-granules because the B-granules failed to initiate. A population segregating for B-granule number was generated by crossing these two accessions and was used to study the genetic basis of B-granule initiation. A combination of Bulked Segregant Analysis and QTL mapping identified a major QTL located on the short arm of chromosome 4S that accounted for 44.4% of the phenotypic variation. The lack of B-granules in polyploid Aegilops with diverse genomes suggests that the B-granule locus has been lost several times independently during the evolution of the Triticeae. It is proposed that the B-granule locus is susceptible to silencing during polyploidization and a model is presented to explain the observed data based on the assumption that the initiation of B-granules is controlled by a single major locus per haploid genome.

Flow cytometric chromosome sorting from diploid progenitors of bread wheat, T. urartu, Ae. speltoides and Ae. tauschii

“…Our findings confirm and expand the results of previous studies indicating the high transferability of COS markers between species (Parida et al 2006;Burt and nicholson 2011;Howard et al 2011;Molnár et al 2013). The fact that 64.2 % of the products obtained with chromosomes isolated from wild relatives were polymorphic relative to those obtained in hexaploid wheat suggested that the substantial genetic diversity of wild progenitors is due to the variability of intron regions (Yu et al 2005).…”

Starch Biosynthesis in the Developing Endosperms of Grasses and Cereals

“…Down-regulation of a pullulanase-type DBE inhibitor activity in barley causes a reduction in the small (B-type) granules, reduces amylose content, alters amylopectin glucan chain-length distribution, and reduces starch content [417]. QTL mapping studies in the wild wheat Aegilops peregrina identified a gene locus, termed Bgc-1 that is located on the short arm of chromosome 4S, which appears to control the initiation or synthesis of B-granules [418]. Recent deletion studies in bread wheat detected orthologous Bgc-1 regions, which, when deleted, result in the loss of B-granules in the endosperm, but interestingly, no yield penalty [419].…”

Effects of environmental factors on cereal starch biosynthesis and composition

“…QTLs are regions of the genome that collectively control a trait and their identification does not rely on a priori knowledge of gene function, since we start with the trait and then work 'backwards' to identify the genes. QTLs affecting starch granule distribution in wheat and barley (Borem et al, 1999;Howard et al, 2011;Igrejas et al, 2002), pasting properties of barley flour and starch synthesis and degradation under stress (Garcia-Suarez et al, 2010;Liu et al, 2008;Pelleschi et al, 2006;Worch et al, 2011) have been identified. The power of the QTL approach may be further enhanced if the traits to be mapped are parameters from eco-physiological models (Reymond et al, 2003).…”