High-Molecular-Weight Glutenin Subunits: Genetics, Structures, and Relation to End Use Qualities

High-molecular-weight glutenin subunits (HMW-GSs) are storage proteins present in the starchy endosperm cells of wheat grain. Encoding the synthesis of HMW-GS, the Glu-1 loci located on the long arms of group 1 chromosomes of the hexaploid wheat (1A, 1B, and 1D) present multiple allelism. In hexaploid wheat cultivars, almost all of them express 3 to 5 HMW-GSs and the 1Ay gene is always silent. Though HMW-GSs are the minor components in gluten, they are crucial for dough properties, and certain HMW-GSs make more positive contributions than others. The HMW-GS acts as a “chain extender” and provides a disulfide-bonded backbone in gluten network. Hydrogen bonds mediated by glutamine side chains are also crucial for stabilizing the gluten structure. In most cases, HMW-GSs with additional or less cysteines are related to the formation of relatively more or less interchain disulfide bonds and HMW-GSs also affect the gluten secondary structures, which in turn impact the end use qualities of dough.

Structure and expression analysis of TaGW5 in common wheat

OsGW5 (OsGSE) regulates cell proliferation and is involved in regulating grain size and thousand-grain weight in rice. Our knowledge about its wheat ortholog TaGW5 is limited. In the present study, we characterized the structure and expression of TaGW5 at molecular level in wheat and predicted the cis-elements and transcription factor binding sites (TFBS) of its promoter. The GW5 orthologs in barley (HvGW5), rice (OsGW5), Triticum turgidum L. (TtGW5) and Brachypodium distachyon (BdGW5) were also identified for comparative analyses. TaGW5 was mapped onto the short arms of group 1 chromosomes (1AS, 1BS, and 1DS). Multiple alignments indicated GW5 possesses three exons and two introns in all the analyzed species except for rice and the exon-intron junction composed of exon 2 and intron 2 was highly conserved. GW5 has a conserved domain (DUF 4005) and two neighboring IQ domains and was mainly expressed in wheat young spikes, in barley immature inflorescences and in rice anthers. Drought, heat and biotic-stress treatments had no significant effects on HvGW5 and TaGW5 expression. Significant correlation between the expression patterns of predicted transcription factor ABF2 and OsGW5 was also detected. Taken together, these results broaden our understanding of GW5 in wheat, barley and rice and will be helpful for further manipulating GW5 and uncovering its roles in plants

Molecular and physical mapping of a barley gene on chromosome arm 1HL that causes sterility in hybrids with wheat

Addition of the long arm of barley chromosome 1H (1HL) to wheat causes severe meiotic abnormalities and complete sterility of the plants. To map the barley gene responsible for the 1H-induced sterility of wheat, a series of addition lines of translocated 1H chromosomes were developed from the crosses between the wheat 'Shinchunaga' and five reciprocal translocation lines derived from the barley line St.13559. Examination of the seed fertility of the addition lines revealed that the sterility gene is located in the interstitial 25% region of the 1HL arm. The genetic location of the sterility gene was also estimated by physically mapping sequence-tagged site (STS) markers and simple-sequence repeat (SSR) markers with known map locations. The sterility gene is designated Shw (sterility in hybrids with wheat). Comparison of the present physical map of 1HL with two previously published genetic maps revealed a paucity of markers in the proximal 30% region and non-random distribution of SSR markers. Two inconsistencies in marker order were found between the present physical map and the consensus genetic map of group 1 chromosomes of Triticeae. On the basis of the effects on meiosis and chromosomal location, the relationship of the present sterility gene with other fertility-related genes of Triticeae is discussed.Key words: Hordeum vulgare, molecular markers, sterility, translocation, wheat–barley chromosome addition line.

Identification and Physical Localization of Useful Genes and Markers to a Major Gene-Rich Region on Wheat Group1SChromosomes

The short arm of Triticeae homeologous group 1 chromosomes is known to contain many agronomically important genes. The objectives of this study were to physically localize gene-containing regions of the group 1 short arm, enrich these regions with markers, and study the distribution of genes and recombination. We focused on the major gene-rich region (“1S0.8 region”) and identified 75 useful genes along with 93 RFLP markers by comparing 35 different maps of Poaceae species. The RFLP markers were tested by gel blot DNA analysis of wheat group 1 nullisomic-tetrasomic lines, ditelosomic lines, and four single-break deletion lines for chromosome arm 1BS. Seventy-three of the 93 markers mapped to group 1 and detected 91 loci on chromosome 1B. Fifty-one of these markers mapped to two major gene-rich regions physically encompassing 14% of the short arm. Forty-one marker loci mapped to the 1S0.8 region and 10 to 1S0.5 region. Two cDNA markers mapped in the centromeric region and the remaining 24 loci were on the long arm. About 82% of short arm recombination was observed in the 1S0.8 region and 17% in the 1S0.5 region. Less than 1% recombination was observed for the remaining 85% of the physical arm length.

Homoeoallelic gene Ncc-tmp of Triticum timopheevii conferring compatibility with the cytoplasm of Aegilops squarrosa in the tetraploid wheat nuclear background

A nuclear gene, Ncc-tmp1A, of Triticum timopheevii is required for the nucleus-cytoplasm (NC) compatibility in tetraploid NC hybrids with the cytoplasm of Aegilops squarrosa. A euploid NC hybrid of T. durum was previously produced by introgressing the gene from chromosome 1A of T. timopheevii. To examine the possible presence of a functional homoeoallele in the G genome of T. timopheevii, segregation of seed viability was studied as a marker phenotype in BC1s involving the two types of NC hybrids, (Ae. squarrosa) - T. timopheevii and (Ae. squarrosa) - T. turgidum. The result of these test crosses suggested that the G genome possesses a functional homoeoallele Ncc-tmp1G. Segregation of two RAPD (random amplified polymorphic DNA) markers that were closely linked to Ncc-tmp1A was further studied among the viable BC1s obtained from a test cross of (Ae. squarrosa) - T. timopheevii × T. turgidum. Some viable BC1 segregants without the markers were obtained, suggesting a limited degree of transmission of chromosome 1G carrying Ncc-tmp1G. However, a similar RAPD analysis of BC1s obtained after backcrosses of reciprocal F1s of T. timopheevii / T. turgidum with T. turgidum showed random marker segregation. Thus, it was concluded that Ncc-tmp1A is not required for compatibility with its own cytoplasm. Southern blot analysis of the euploid NC hybrid using RFLP (restriction fragment length polymorphism) markers on the homoeologous group 1 chromosomes showed that Ncc-tmp1A locates in the centromeric region.Key words: nucleus-cytoplasm (NC) compatibility, Ncc genes, Aegilops squarrosa, Triticum timopheevii, durum wheat.

Segregation of glutenins in wheat × maize-derived doubled haploid wheat populations

The segregation of both high and low molecular weight glutenin subunits across 7 F1 wheat (Triticum aestivum L.) × maize (Zea mays L.) derived doubled haploid populations was examined. The F1 wheats used in each population were produced from parents of interest to Australian wheat breeding programs. The parents varied by up to 5 glutenin subunit loci. Examination of subunits individually within each population using a chi-square analysis revealed that all but 2 of the 26 pairs of alleles analysed fitted the expected 1 : 1 segregation ratio. Glutenin profiles were examined for each cross individually and all but one (Sonalika/Hartog) fitted the expected Mendelian segregation pattern. The analysis of allele distribution of the 6 glutenin loci across all 7 crosses showed all falling well within expected segregation ratios. Closer examination of parental lines and populations revealed irregularities which conflict with original assumptions and provide a valid explanation for the few segregation distortions observed. It is concluded that wheat × maize-derived doubled haploid populations represent a unbiased assortment of parental gametes on both arms of Group 1 chromosomes.