Stacking HMW-GS transgenes in bread wheat: Combining subunit 1Dy10 gives improved mixing properties and dough functionality

Proteomic Analysis of Proteins Responsive to Drought and Low Temperature Stress in a Hard Red Spring Wheat Cultivar

Drought stress is becoming more prevalent with global warming, and has been shown to have large effects on gluten proteins linked to wheat bread making quality. Likewise, low temperature stress can detrimentally affect proteins in wheat. This study was done to determine the differential abundance of high molecular weight (HMW) glutenin proteins in a drought and low temperature stressed high quality hard red spring wheat cultivar (PAN3478), against a control. The treatments were applied in the greenhouse at the soft dough stage. HMW glutenin proteins were extracted from the flour, and were separated by using two-dimensional gel electrophoresis. Protein spots that had p values lower than 0.05 and fold values equal to or greater than 1.2 were considered to be significantly differentially abundant. These proteins were further analyzed by using tandem mass spectrometry. There was a 1.3 to 1.8 fold change in 17 protein spots due to the cold treatment. The drought treatment caused a 1.3 to 3.8 fold change in 19 protein spots. These spots matched either HMW or low molecular weight (LMW) glutenin subunits. In the latter case, the C subunits of LMW glutenins were notably found to be up-regulated under both stress conditions. All the proteins that have been identified can directly influence dough characteristics. Data are available via ProteomeXchange with the identifier PXD017578.

Efficient isolation of ion beam-induced mutants for homoeologous loci in common wheat and comparison of the contributions of Glu-1 loci to gluten functionality

Ion beam mutations can be efficiently isolated and deployed for functional comparison of homoeologous loci in polyploid plants, and Glu - 1 loci differ substantially in their contribution to wheat gluten functionality. To efficiently conduct genetic analysis, it is beneficial to have multiple types of mutants for the genes under investigation. Here, we demonstrate that ion beam-induced deletion mutants can be efficiently isolated for comparing the function of homoeologous loci of common wheat (Triticum aestivum). Through fragment analysis of PCR products from M2 plants, ion beam mutants lacking homoeologous Glu-A1, Glu-B1 or Glu-D1 loci, which encode high molecular weight glutenin subunits (HMW-GSs) and affect gluten functionality and end-use quality of common wheat, could be isolated simultaneously. Three deletion lines missing Glu-A1, Glu-B1 or Glu-D1 were developed from the original mutants, with the Glu-1 genomic regions deleted in these lines estimated using newly developed DNA markers. Apart from lacking the target HMW-GSs, the three lines all showed decreased accumulation of low molecular weight glutenin subunits (LMW-GSs) and increased amounts of gliadins. Based on the test data of five gluten and glutenin macropolymer (GMP) parameters obtained with grain samples harvested from two environments, we conclude that the genetic effects of Glu-1 loci on gluten functionality can be ranked as Glu-D1 > Glu-B1 > Glu-A1. Furthermore, it is suggested that Glu-1 loci contribute to gluten functionality both directly (by promoting the formation of GMP) and indirectly (through keeping the balance among HMW-GSs, LMW-GSs and gliadins). Finally, the efficient isolation of ion beam mutations for functional comparison of homoeologous loci in polyploid plants and the usefulness of Glu-1 deletion lines for further studying the contribution of Glu-1 loci to gluten functionality are discussed.

The interactive effects of transgenically overexpressed 1Ax1 with various HMW-GS combinations on dough quality by introgression of exogenous subunits into an elite Chinese Wheat variety

Seed storage proteins in wheat endosperm, particularly high-molecular-weight glutenin subunits (HMW-GS), are primary determinants of dough properties, and affect both end-use quality and grain utilization of wheat (Triticum aestivum L). In order to investigate the interactive effects between the transgenically overexpressed 1Ax1 subunit with different HMW-GS on dough quality traits, we developed a set of 8 introgression lines (ILs) overexpressing the transgenic HMW-glutenin subunit 1Ax1 by introgression of this transgene from transgenic line B102-1-2/1 into an elite Chinese wheat variety Chuanmai107 (C107), using conventional crossing and backcrossing breeding technique. The donor C107 strain lacks 1Ax1 but contains the HMW-GS pairs 1Dx2+1Dy12 and 1Bx7+1By9. The resultant ILs showed robust and stable expression of 1Ax1 even after five generations of self-pollination, and crossing/backcrossing three times. In addition, overexpression of 1Ax1 was compensated by the endogenous gluten proteins. All ILs exhibited superior agronomic performance when compared to the transgenic parent line, B102-1-2/1. Mixograph results demonstrated that overexpressed 1Ax1 significantly improved dough strength, resistance to extension and over-mixing tolerance, in the targeted wheat cultivar C107. Further, comparisons among the ILs showed the interactive effects of endogenous subunits on dough properties when 1Ax1 was overexpressed: subunit pair 17+18 contributed to increased over-mixing tolerance of the dough; expression of the Glu-D1 allele maintained an appropriate balance between x-type and y-type subunits and thereby improved dough quality. It is consistent with ILs C4 (HMW-GS are 1, 17+18, 2+12) had the highest gluten index and Zeleny sedimentation value. This study demonstrates that wheat quality could be improved by using transgenic wheat overexpressing HMW-GS and the feasibility of using such transgenic lines in wheat quality breeding programs.

Wheat storage proteins in transgenic rice endosperm

Transgenic rice seed expressing wheat HMW glutenin subunit was characterized to study the effects of the wheat prolamin on the protein expression pattern and protein size distribution in the endosperm and the functional and rheological properties of the rice flour and dough. Significant differences were found in the protein expression pattern between the transgenic and wild type samples. Comparing the protein expression profiles of transgenic and nontransgenic plants, combined with proteomic-based studies, indicated increased protein disulfide isomerase (PDI) levels in the transgenic rice lines. The accurate molecular size of HMW-GS in rice endosperm was identified by MALDI-TOF-MS analysis. The expressed wheat HMW (subunit 1Dx5) GS showed a positive effect on the functional properties of rice dough by significantly increasing the size distribution of the polymeric protein fraction and modifying the dough mixing parameters.

Coexpression of the high molecular weight glutenin subunit 1Ax1 and puroindoline improves dough mixing properties in durum wheat (Triticum turgidum L. ssp. durum)

Wheat end-use quality mainly derives from two interrelated characteristics: the compositions of gluten proteins and grain hardness. The composition of gluten proteins determines dough rheological properties and thus confers the unique viscoelastic property on dough. One group of gluten proteins, high molecular weight glutenin subunits (HMW-GS), plays an important role in dough functional properties. On the other hand, grain hardness, which influences the milling process of flour, is controlled by Puroindoline a (Pina) and Puroindoline b (Pinb) genes. However, little is known about the combined effects of HMW-GS and PINs on dough functional properties. In this study, we crossed a Pina-expressing transgenic line with a 1Ax1-expressing line of durum wheat and screened out lines coexpressing 1Ax1 and Pina or lines expressing either 1Ax1 or Pina. Dough mixing analysis of these lines demonstrated that expression of 1Ax1 improved both dough strength and over-mixing tolerance, while expression of PINA detrimentally affected the dough resistance to extension. In lines coexpressing 1Ax1 and Pina, faster hydration of flour during mixing was observed possibly due to the lower water absorption and damaged starch caused by PINA expression. In addition, expression of 1Ax1 appeared to compensate the detrimental effect of PINA on dough resistance to extension. Consequently, coexpression of 1Ax1 and PINA in durum wheat had combined effects on dough mixing behaviors with a better dough strength and resistance to extension than those from lines expressing either 1Ax1 or Pina. The results in our study suggest that simultaneous modulation of dough strength and grain hardness in durum wheat could significantly improve its breadmaking quality and may not even impair its pastamaking potential. Therefore, coexpression of 1Ax1 and PINA in durum wheat has useful implications for breeding durum wheat with dual functionality (for pasta and bread) and may improve the economic values of durum wheat.

Down-regulating γ-gliadins in bread wheat leads to non-specific increases in other gluten proteins and has no major effect on dough gluten strength

Background

Gliadins are a major component of gluten proteins but their role in the mixing of dough is not well understood because their contribution to wheat flour functional properties are not as clear as for the glutenin fraction.

Methodology/Principal Findings

Transgenic lines of bread wheat with γ-gliadins suppressed by RNAi are reported. The effects on the gluten protein composition and on technological properties of flour were analyzed by RP-HPLC, by sodium dodecyl sulfate sedimentation (SDSS) test and by Mixograph analysis. The silencing of γ-gliadins by RNAi in wheat lines results in an increase in content of all other gluten proteins. Despite the gluten proteins compensation, in silico analysis of amino acid content showed no difference in the γ-gliadins silenced lines. The SDSS test and Mixograph parameters were slightly affected by the suppression of γ-gliadins.

Conclusions/Significance

Therefore, it is concluded that γ-gliadins do not have an essential functional contribution to the bread-making quality of wheat dough, and their role can be replaced by other gluten proteins.