D.C. Liu

The Crossability of Triticum turgidum with Aegilops tauschii

Two experiments to investigate the crossability of Triticum turgidum with Aegilops tauschii are described. In the first experiment, 372 wide hybridization combinations were done by crossing 196 T. turgidum lines belonging to seven subspecies with 13 Ae. tauschii accessions. Without embryo rescue and hormone treatment, from the 66220 florets pollinated, 3713 seeds were obtained, with a mean crossability percentages of 5.61% which ranged from 0 to 75%. A lot of hybrid seeds could germinate and produce plants. Out of 372 combinations, 73.12% showed a very low crossability less than 5%, 23.39% showed the crossability of 5–30%, 2.69% showed the crossability of 30–50%, 0.81% showed high crossability more than 50%, respectively. Among the seven T. turgidum subspecies, there were significant differences in crossability. The ssp. dicoccoides and dicoccon showed the highest crossability, while polonicum the lowest. All the crossability percentages more than 30% were obtained from the crossing of ssp. dicoccoides or...

Characterization of HMW-GS genes Dx5 t and Dy12 t from Aegilops tauschii accession with subunit combination Dx5 t + Dy12 t

Aegilops tauschii is the generally accepted D genome diploid donor of hexaploid wheat. The significance of Ae. tauschii HMW-GS genes on bread-making properties of bread wheat has been well documented. Among them, Ae. tauschii HMW-GS Dx5 t +Dy12 t was thought as the pair with potentially value in endowing synthetic hexaploid wheat with good end-use qualities. In this paper, we isolated and sequenced genes Dx5 t and Dy12 t from Ae. tauschii accession As63. Amino acid sequence comparison indicated that Dy12 t from Ae. tauschii is more similar to Dy10 rather than Dy12 of bread wheat. The sequence of Dx5 t in Ae. tauschii accession As63 showed higher similarity to that of Dx5 in bread wheat than others. However, it is notable that Dx5 t lacked the additional cysteine residue in Dx5, which is responsible for good bread-making quality in common wheat. Moreover, compared to Dx5, Dx5 t has an extra hexpeptide repetitive motif unit (SGQGQQ) as well as five amino acid substitutions.

Identification of a candidate gene for Rc-D1, a locus controlling red coleoptile colour in wheat

Red coleoptile is an easily observed agronomic trait of wheat and has been extensively studied. However, the molecular mechanism of this trait has not yet been revealed. In this study, the MYB gene TaMYB-D1 was isolated from the wheat cultivar ‘Gy115’, which possesses red coleoptiles. This gene resided at the short arm of the homoelogous group 7 chromosomes. TaMYB-D1 was the only gene expressed in the coleoptiles of ‘Gy115’ and was not expressed in ‘Opata’ and ‘CS’, which have uncoloured coleoptiles. Phylogenetic analysis placed TaMYB-D1 very close to ZmC1 and other MYB proteins regulating anthocyanin biosynthesis. The encoded protein of TaMYB-D1 had an integrated DNA binding domain of 102 amino acids and a transcription domain with 42 amino acids, similar to the structure of ZmC1. Transient expression analysis in onion epidermal cells showed that TaMYB-D1 was located at the plant nucleus, which suggested its role as a transcription factor. The expression of TaMYB-D1 was accompanied with the expression of TaDFR and anthocyanin biosynthesis in the development of the coleoptile of ‘Gy115’. Transient expression analysis showed that only TaMYB-D1 induced a few ‘Opata’ coleoptile cells to synthesize anthocyanin in light, and the gene also induced a colour change to red in many cells with the help of ZmR. All of these results suggested TaMYB-D1 as the candidate gene for the red coleoptile trait of ‘Gy115’.

Isolation and characterization of a novel HMW-GS Glu-Dx allele from Tibet bread wheat landrace

A novel HMW-GS of Dx5** with slightly faster migration rate than that of Dx5, was found in a Tibet bread wheat landrace using SDS-PAGE. Moreover, Dx5** is the subunit with the fastest migration rate in Glu-Dx locus. The gene for this subunit was isolated and its sequence was obtained in the present study. This gene was very similar to Dx5 both in nucleotide and deduced amino acid sequence. At the nucleotide sequence level, Dx5** different from Dx5 by the deletion of a 27 bp fragment and two nucleotide replacements at position 353(G/C) and 692(C/G), respectively. At the amino acid sequence level, Dx5** different from Dx5 by the deletion of a hexaploid (LGQGQQ) and a tripeptide (GQQ) repetitive motif and two amino acid replacements at position 118(C/S) and 231(A/G), respectively. These results suggested that the Dx5** was a derivation of Dx5 and was formed by replication slippage. Moreover, the specific cysteine (C) located at the beginning of the repetitive domain of Dx5, which proved to be critical for the end-use quality of wheat flours, was replaced by serine (S) in Dx5**.

Allelic Variation and Transcriptional Isoforms of Wheat TaMYC1 Gene Regulating Anthocyanin Synthesis in Pericarp

Recently the TaMYC1 gene encoding bHLH transcription factor has been isolated from the bread wheat (Triticum aestivum L.) genome and shown to co-locate with the Pp3 gene conferring purple pericarp color. As a functional evidence of TaMYC1 and Pp3 being the same, higher transcriptional activity of the TaMYC1 gene in colored pericarp compared to uncolored one has been demonstrated. In the current study, we present additional strong evidences of TaMYC1 to be a synonym of Pp3. Furthermore, we have found differences between dominant and recessive Pp3(TaMyc1) alleles. Light enhancement of TaMYC1 transcription was paralleled with increased AP accumulation only in purple-grain wheat. Coexpression of TaMYC1 and the maize MYB TF gene ZmC1 induced AP accumulation in the coleoptile of white-grain wheat. Suppression of TaMYC1 significantly reduced AP content in purple grains. Two distinct TaMYC1 alleles (TaMYC1p and TaMYC1w) were isolated from purple- and white-grained wheat, respectively. A unique, compound cis-acting regulatory element had six copies in the promoter of TaMYC1p, but was present only once in TaMYC1w. Analysis of recombinant inbred lines showed that TaMYC1p was necessary but not sufficient for AP accumulation in the pericarp tissues. Examination of larger sets of germplasm lines indicated that the evolution of purple pericarp in tetraploid wheat was accompanied by the presence of TaMYC1p. Our findings may promote more systematic basic and applied studies of anthocyanins in common wheat and related Triticeae crops.

Molecular characterization of seven novel Glu-A1mx alleles from Triticum monococcum ssp. monococcum

Seven Glu-A1m allelic variants of the Glu-A1mx genes in Triticum monococcum ssp. monococcum, designated as 1Ax2.1a, 1Ax2.1b, 1Ax2.1c, 1Ax2.1d, 1Ax2.1e, 1Ax2.1f, and 1Ax2.1g were characterized. Their authenticity was confirmed by successful expression of the coding regions in E. coli, and except for the 1Ax2.1a with the presence of internal stop codons at position of 313 aa, all correspond to the subunit in seeds. However, all the active six genes had a same DNA size although their encoding subunits showed different molecular weight. Our study indicated that amino acid residue substitutions rather than previously frequently reported insertions/deletions played an important role on the subunit evolution of these Glu-A1mx alleles. Since variation in the Glu-A1x locus in common wheat is rare, these novel genes at the Glu-A1mx can be used as candidate genes for further wheat quality improvement.

Molecular characterization of different Triticum monococcum ssp. monococcum Glu-A1mx alleles

High-molecular-weight glutenin subunits (HMW-GSs) are important seed storage proteins associated with bread-making quality in common wheat (Triticum aestivum L., 2n = 6x = 42, AABBDD). Variation in the Glu-A1x locus in common wheat is scare. Diploid Triticum monococcum ssp. monococcum (2n = 2x = 14, AmAm) is the first cultivated wheat. In the present study, allelic variations at the Glu-A1mx locus were systematically investigated in 197 T. monococcum ssp. monococcum accessions. Out of the 8 detected Glu-A1mx alleles, 5 were novel, including Glu-A1m-b, Glu-A1m-c, Glu-A1m-d, Glu-A1m-g, and Glu-A1m-h. This diversity is higher than that of common wheat. Compared with 1Ax1 and 1Ax2*, which are present in common wheat, these alleles contained three deletions/insertions as well as some single nucleotide polymorphism variations that might affect the elastic properties of wheat flour. New variations in T. monococcum probably occurred after the divergence between A and Am and are excluded in common wheat population...

The transfer to and functional annotation of alien alleles in advanced wheat lines derived from synthetic hexaploid wheat

The abundant genetic diversity in synthetic hexaploid wheat (SHW) can achieve breakthroughs in wheat genetic improvement, but little is known of the genetic mechanisms involved. In this study, three populations of advanced lines (totaling 284 individuals), derived from three top-crosses of SHW-L1 with different common wheat cultivars, followed by ten generations of artificial selection, were used to evaluate the transfer of alien alleles with 24872 Diversity Arrays Technology (DArT) markers. Only 1824, 1786 and 1514 DArT markers were needed to distinguish the alleles from SHW-L1 and the other common wheat parent in the populations SCPD, SS7M and SSYZ, respectively. The data clearly showed that all the advanced lines contained alien alleles from SHW-L1. The lowest percentage of alien alleles was 6.97% in an advanced line in population SSYZ, while the biggest was 30.41% in a SCPD advanced lines. The percentages of alien alleles at each locus ranged from 0% to 100% in all three populations. Forty-four alien alleles did not exist in all advanced lines, while two alien alleles were present in all advanced lines. Two of the 100% alien alleles were associated with thousand-grain weight and leaf rust resistance. Thirteen alien alleles were associated with grain yield, grain thickness and width, thousand-grain weight, grain weight/ear, plant height, grain weight, grain number, powdery mildew resistance, spikelet number per spike or yellow rust resistance. The research provided direct evidence of the existence of alien alleles in advanced lines and detected a number of valuable alleles related to wheat yield or disease resistance. More research is needed to analyze the functional mechanisms of these alleles, and to use these materials and alleles in wheat improvement.

Genome-wide association analysis of kernel morphology in breeding lines derived from synthetic hexaploid wheat in Qinghai Province, China

Wheat kernel morphology is a very important trait for wheat yield improvement. This is the first report of association analysis of kernel morphology traits in wheat breeding lines. In Qinghai, China, the research described here involved genome-wide association analysis in breeding lines derived from synthetic hexaploid wheat with a mixed linear model to identify the quantitative trait loci (QTLs) related to kernel morphology. The 8033 effective Diversity Array Technology (DArT) markers produced a genetic map of 5901.84 cM with an average density of 1.36 markers/cM. Population structure analysis classified 507 breeding lines into three groups by Bayesian structure analysis using unlinked markers. Linkage disequilibrium decay was observed with a map coverage of 2.78 cM. Marker-trait association analysis showed that 15 DArT markers for kernel morphology were detected, located on nine chromosomes, and explained 2.6%–4.0% of the phenotypic variation of kernel area (KA), kernel width (KW), kernel length (KL) and thousand-kernel weight (TKW). The marker 1139297 was related to both the KL and KA traits. Only six DArT markers were close to known QTLs. The parent SHW-L1 carried eight favored alleles, while other seven favored alleles were derived from elite common wheat cultivars. These QTLs, identified in elite breeding lines, should help us understand the kernel morphology trait better, and to provide germ-plasm for breeding new wheat cultivars for Qinghai Province or other regions.

Characterization of an expressed Triticum monococcum Glu-A1y gene containing a premature termination codon in its C-terminal coding region

Premature termination codons (PTCs) are an important reason for the silence of high-molecular-weight glutenin subunits in Triticum species. Although the Glu-A1y gene is generally silent in common wheat, we here isolated an expressed Glu-A1y gene containing a PTC, named 1Ay8.3, from Triticum monococcum ssp. monococcum (AmAm, 2n = 2x = 14). Despite the presence of a PTC (TAG) at base pair positions 1879–1881 in the C-terminal coding region, this did not obviously affect 1Ay8.3 expression in seeds. This was demonstrated by the fact that when the PTC TAG of 1Ay8.3 was mutated to the CAG codon, the mutant in Escherichia coli bacterial cells expressed the same subunit as in the seeds. However, in E. coli, 1Ay8.3 containing the PTC expressed a truncated protein with faster electrophoretic mobility than that in seeds, suggesting that PTC translation termination suppression probably occurs in vivo (seeds) but not in vitro (E. coli). This may represent one of only a few reports on the PTC termination suppression phenomenon in genes.