Characterization of the HMW glutenin subunits from Aegilops searsii and identification of a novel variant HMW glutenin subunit

Abstract

High molecular weight (HMW) glutenin subunits are conserved seed storage proteins in wheat and related species. Here we describe a more detailed characterization of the HMW glutenin subunits from Aegilops searsii, which is diploid and contains the S(s) genome related to the S genome of Aegilops speltoides and the A, B and D genomes of hexaploid wheat. SDS-PAGE experiments revealed two subunits (one x and one y) for each of the nine Ae. searsii accessions analyzed, indicating that the HMW glutenin subunit gene locus of Ae. searsii is similar to the Glu-1 locus found in wheat in containing both x and y genes. The primary structure of the four molecularly cloned subunits (from two Ae. searsii accessions) was highly similar to that of the previously reported x and y subunits. However, in one accession (IG49077), the last 159 residues of the x subunit (1S(s)x49077), which contained the sequence element GHCPTSPQQ, were identical to those of the y subunit (1S(s)y49077) from the same accession. Consequently, 1S(s)x49077 contains an extra cysteine residue located at the C-terminal part of its repetitive domain, which is novel compared to the x-type subunits reported so far. Based on this and previous studies, the structure and expression of the Glu-1 locus in Ae. searsii is discussed. A hypothesis on the genetic mechanism generating the coding sequence for the novel 1S(s)x49077 subunit is presented.

Novel x-Type High-Molecular-Weight Glutenin Genes From Aegilops tauschii and Their Implications on the Wheat Origin and Evolution Mechanism of Glu-D1-1 Proteins

“…tauschii have been characterized (Wan et al 2005). Evidence from molecular analysis demonstrated that the HMW glutenin subunits from wheat and related species have highly conserved structures, consisting of a signal peptide (21 residues), an N-terminal domain (86-89 residues in x-type and 104 in y-type subunits), a C-terminal domain (42 residues), and a central repetitive domain (630-830 residues) that is mainly responsible for differences in molecular weight of the subunits Wan et al 2002Wan et al , 2005Yan et al 2004;Sun et al 2006;Zhang et al 2006). The HMW glutenin genes, therefore, could derive from a common ancestor.…”

Molecular characterization of a novel HMW glutenin subunit Dx2.3*tfromAegilops tauschii

“…Previously, Anderson and Greene (1989) suggested the following modes may results in sequence alteration: (i) single base and single repeat; (ii) deletions or additions with a repeat; (iii) deletions or duplications of blocks of repeats, with possible unequal crossover and slip-mismatching. The unequal crossover was detected in Aegilops searsii accession IG49077, which results into the recombinant of Glu-1 loci (Sun et al 2006). Based on the result that the 68 residues in the repetitive domain of 1Dx2.3* t were identical to those of the y-type subunits, we suggest that unequal crossing over between the two Glu-1 loci on the sister chromatids of the homologous chromosomes during meiosis might have resulted into the formation of this novel hybrid ORF (Fig.…”

“…For example, an extra cystenin was detected in the N-terminal part of the repetitive domain of 1Dx5 subunit and this subunit has been frequently associated with improved processing quality in wheat varieties . 1S s x490771 contains an extra cystenin residue located at the C-terminal part of its repetitive domain, which is novel compared to x-type subunits reported before (Sun et al 2006). Although the size of N-and C-terminal domains is highly conserved in either x-and y-type subunits, the repetitive domain size is usually variable.…”

Novel LMW glutenin subunit genes from wild emmer wheat (Triticum turgidum ssp. dicoccoides) in relation to Glu-3 evolution

“…For example, a γ-gliadin/LMW-GS chimeric gene was identified in wheat (Nagy et al 2005). In addition, one HMW-GS y-/x-type chimeric gene was characterized from Aegilops searsii (Sun et al 2006). Novel chimeric genes (between LMW-i-and LMW-m-type LMW-GSs) were isolated from both Aegilops kotschyi and Aegilops juvenalis (Li et al 2008a).…”