Novel variants of HMW glutenin subunits from Aegilops section Sitopsis species in relation to evolution and wheat breeding

Abstract

BackgroundHigh molecular weight glutenin subunits (HMW-GSs), encoded by the genes at Glu-1 loci in wheat and its related species, are significant in the determination of grain processing quality. However, the diversity and variations of HMW-GSs are relatively low in bread wheat. More interests are now focused on wheat wild relatives in Triticeae. The genus Aegilops represents an important germplasm for novel HWM-GSs and other useful genes for wheat genetic improvement.ResultsSix novel Glu-1 alleles and HMW-GSs were identified and characterized from three species of Aegilops section Sitopsis (S genome). Both open reading frames (ORFs) and promoter regions of these Glu-1 alleles were sequenced and characterized. The ORFs of Sitopsis Glu-1 genes are approximately 2.9 kb and 2.3 kb for x-type and y-type subunits, respectively. Although the primary structures of Sitopsis HMW-GSs are similar to those of previously reported ones, all six x-type or y-type subunits have the large fragment insertions. Our comparative analyses of the deduced amino acid sequences verified that Aegilops section Sitopsis species encode novel HMW-GSs with their molecular weights larger than almost all other known HMW-GSs. The Glu-1 promoter sequences share the high homology among S genome. Our phylogenetic analyses by both network and NJ tree indicated that there is a close phylogenetic evolutionary relationship of x-type and y-type subunit between S and D genome.ConclusionsThe large molecular weight of HMW-GSs from S genome is a unique feature identified in this study. Such large subunits are resulted from the duplications of repetitive domains in Sitopsis HMW-GSs. The unequal crossover events are the most likely mechanism of variations in glutenin subunits. The S genome-encoded subunits, 1Dx2.2 and 1Dx2.2* have independent origins, although they share similar evolutionary mechanism. As HMW-GSs play a key role in wheat baking quality, these large Sitopsis glutenin subunits can be used as special genetic resources for wheat quality improvement.

Characterization of a novel 4.0-kb y-type HMW-GS fromEremopyrum distans

“…Unequal crossover events and slip-mismatching have been suggested as the most likely mechanisms for size variations in HMW-GSs. A detailed comparison of the large HMW-GSs Dx 2.2 and Dx 2.2* as well as Sx 2.9 with Dx 2 have indicated that they have different numbers and lengths of repeatable blocks (Jiang et al 2012;Wan et al 2005). Such duplications most likely arose by unequal crossing over during meiosis (D'Ovidio et al 1996).…”

“…HMW-GSs with large molecular size have attracted considerable research interest. Some of the largest reported HMW-GS genes include Ux from Aegilops umbellulata (Liu et al 2003), Sx from the Sitopsis section of Aegilops (Sun et al 2006;Jiang et al 2012), and the Dx subunits Dx 2.2 and Dx 2.2* from hexaploid wheat (Wan et al 2005). The open reading frames (ORFs) of these genes typically consist of about 3.0 kb in nucleotides and approximately 100-106 kDa in mature protein.…”

Transfer of HMW glutenin subunits from Aegilops kotschyi to wheat through radiation hybridization

“…longissima and Ae. sharonensis also corresponded to the Glu1Bx7 of the Chinese Spring (Jiang et al 2012). Ma et al (2013) characterized five novel HMWGS from different accessions of Ae.…”

Characterization of x-type high-molecular-weight glutenin promoters (x-HGP) from different genomes in Triticeae

“…Each Glu-1 locus consists of 2 tightly linked genes encoding an x-type subunit with a larger molecular weight and a y-type subunit with a smaller one, respectively ( Payne 1987 ). Up to now, a lot of studies have been conducted in identifications and function analysis of HMW-GS genes from wheat and its wild relatives ( Anderson and Greene 1989 ; Forde et al 1985 ; Halford et al 1987 ; Jiang et al 2012a ; Jiang et al 2012b ; Jiang et al 2009 ; Liu et al 2003, 2007, 2008, 2010 ; Sugiyama et al 1985 ; Thompson et al 1985 ; Wan et al 2005 ).…”

“…The grasses of the Triticeae tribe include huge number of wheat and its relatives, which has been widely researched as genetic resource for wheat quality improvement programs. For example, previous reports revealed that wild species has abundant HMW-GS variants which confers to different structural feature and expression level from those of common wheat (Jiang et al 2012a ; Liu et al 2010 ; Wan et al 2002 ; 2005 ).…”