Gavin Humphreys

Integrated analysis of seed proteome and mRNA oxidation reveals distinct post‐transcriptional features regulating dormancy in wheat (Triticum aestivum L.)

Wheat seeds can be released from a dormant state by after-ripening; however, the underlying molecular mechanisms are still mostly unknown. We previously identified transcriptional programmes involved in the regulation of after-ripening-mediated seed dormancy decay in wheat (Triticum aestivum L.). Here, we show that seed dormancy maintenance and its release by dry after-ripening in wheat is associated with oxidative modification of distinct seed-stored mRNAs that mainly correspond to oxidative phosphorylation, ribosome biogenesis, nutrient reservoir and α-amylase inhibitor activities, suggesting the significance of post-transcriptional repression of these biological processes in regulating seed dormancy. We further show that after-ripening induced seed dormancy release in wheat is mediated by differential expression of specific proteins in both dry and hydrated states, including those involved in proteolysis, cellular signalling, translation and energy metabolism. Among the genes corresponding to these proteins, the expression of those encoding α-amylase/trypsin inhibitor and starch synthase appears to be regulated by mRNA oxidation. Co-expression analysis of the probesets differentially expressed and oxidized during dry after-ripening along with those corresponding to proteins differentially regulated between dormant and after-ripened seeds produced three co-expressed gene clusters containing more candidate genes potentially involved in the regulation of seed dormancy in wheat. Two of the three clusters are enriched with elements that are either abscisic acid (ABA) responsive or recognized by ABA-regulated transcription factors, indicating the association between wheat seed dormancy and ABA sensitivity.

WHEAT-LEGUME COMPOSITE FLOUR QUALITY

Wheat-legume composite flours were produced by blending Canada Western Extra Strong (CWES) and Canada Western Red Spring (CWRS) wheat with varying amounts of three legume proteins. Legume protein addition produced breads with lower specific loaf volume, coarser crumb and firmer texture, and cooked white-salted noodles with greater compression stress and less cutting stress than the wheat controls. The CWES wheat compensated for the negative baking effects of the legume proteins as much as the CWRS wheat. End-use quality did not change at 2% soybean protein addition. Yellow pea protein produced the greatest quality changes, followed by chickpea and soybean protein.

The effect of the environment on the grain colour and quality of commercially grown Canada hard white spring wheat, Triticum aestivum L. ‘Snowbird’

Lukow, O. M., Adams, K., Suchy, J., DePauw, R. M. and Humphreys, G. 2013. The effect of the environment on the grain colour and quality of commercially grown Canada hard white spring wheat, Triticum aestivum L. ‘Snowbird’. Can. J. Plant Sci. 93: 1-11. One of the main advantages of hard white wheat is its lighter grain colour, which can produce visually appealing lighter-coloured end-products. However, grain colour variation can be a concern due to a lack of consistency. This study was carried out to determine the effect of the environment on commercially grown hard white wheat grain colour and wheat grading. More than 1100 samples of the cultivar Snowbird were collected from elevators across western Canada during the 2003 to 2007 crop years. Grain and wholemeal colours were recorded using the CIE L* a* b* scale. Samples were analyzed for grain properties including dimensions, hardness and protein content. Variation in grain colour was mostly attributed to annual fluctuations in climatic conditions (71-79%) and agro-climates (13-18%). Grain ranged in colour from white and bright to dark grey-red. Grain brightness was very highly correlated with grain yellowness. Grain a* and b* were inversely related to grade indicating that higher quality grain was redder and more yellow than lower grades. Warmer and drier environments showed reduced grain yields but produced on average better quality grain with higher protein content.

Effect of Extraction Methods and Wheat Cultivars on Gluten Functionality

The functionality of gluten extracted from Canada Western Red Spring (CWRS) and Canada Western Extra Strong (CWES) wheat flours was evaluated and compared. The extra-strong wheat cultivars had stronger dough properties and produced smaller bread loaves than AC Barrie. Modifications of a starch displacement gluten extraction method were evaluated. For optimal gluten formation and extraction, water to flour ratio of 0.87% and dough mixing to 30% after peak dough development were used. Water and cold ethanol were compared for their effectiveness in gluten extraction by evaluating gluten yield and functionality in a soft wheat flour blend. The ethanol method produced higher yields of gluten, but these gluten extracts had significantly lower protein contents than the respective glutens extracted with water. Farinograph analyses of soft wheat flour fortified with gluten extracts to 14.5% protein content showed significant differ- ences in dough development time, stability and mixing tolerance index between water- and ethanol-extracted gluten ex- tracts; glutens extracted with ethanol had significantly stronger dough properties and also had higher 50PI:50PS gluten ra- tios. Whereas ethanol-extracted gluten decreased or had no effect on loaf volume, water-extracted gluten improved bread loaf volumes when added to soft wheat flour. The inherent differences in quality between CWRS and CWES flour was re- flected in the gluten extracted by water, but not in the gluten extracted by ethanol.

Wheat seed proteins regulated by imbibition independent of dormancy status.

Seed dormancy is an important trait in wheat (Trticum aestivum L.) and it can be released by germination-stimulating treatments such as after-ripening. Previously, we identified proteins specifically associated with after-ripening mediated developmental switches of wheat seeds from the state of dormancy to germination. Here, we report seed proteins that exhibited imbibition induced co-regulation in both dormant and after-ripened seeds of wheat, suggesting that the expression of these specific proteins/protein isoforms is not associated with the maintenance or release of seed dormancy in wheat.

Grain Yield, Starch Content and Activities of Key Enzymes of Waxy and Non-waxy Wheat (Triticum aestivum L.)

Waxy wheat has unique end-use properties; however, its production is limited due mainly to its low grain yield compared with non-waxy wheat. In order to increase its grain yield, it is critical to understand the eco-physiological differences in grain filling between the waxy and non-waxy wheat. In this study, two waxy wheat and two non-waxy wheat cultivars were used to investigate the differences in starch-associated enzymes processes, sucrose and starch dynamics, yield components, and the final grain yield. The results indicated that the mean total grain starch and amylose content, the average 1000-kernel weight and grain yield of the waxy wheat were lower than those of the non-waxy wheat at maturity. The amylose content was significantly and positively correlated with the activity of GBSS (r = 0.80, p < 0.01). Significant positive correlation also exists among activities of AGPase, SSS, GBSS, and SBE, except for GBSS-SBE. In summary, our study has revealed that the reduced conversion of sucrose to starch in the late grain filling stage is the main cause for the low kernel weight and total starch accumulation of the waxy wheat. The reduced conversion also appears to be a factor contributing to the lower grain yield of the waxy wheat.

Hard white spring wheat line WS175 with a high level of resistance to Fusarium head blight

Abstract: WS175 is a hard white spring wheat line with the parentage Snowbird/Sumai3 with a high level of resistance to Fusarium head blight (FHB) that was developed using marker-assisted selection. WS175 contains haplotypes similar to Sumai3 at the loci previously associated with FHB resistance, located on chromosomes 3B, 5A, and 6B. WS175 has similar maturity and protein content, but has lower grain yield, compared to Snowbird. The combination of white seed coat colour and very high level of FHB resistance will make WS175 a valuable parent for the improvement of FHB resistance in white spring wheat breeding programs.

Stem Rust Resistance: Two Approaches

Stem rust, caused by Puccinia graminis f.sp. tritici (Pgt), is a destructive disease of wheat that has historically caused significant yield losses in much of the global wheat production area. Over the past 50 years, stem rust has been effectively controlled by deploying cultivars carrying stem rust resistance (Sr) genes. With the emergence of new Pgt races, namely Ug99 and its variants, there has been a reinvestment in stem rust research. This includes discovery, characterization, genetic mapping, and cloning of Sr genes. Here we investigated two such examples of genetic characterization and mapping of stem rust resistance. In the first example, a region on chromosome 6DS harbouring resistance to Ug99 was examined in several populations and from several sources. In the second example, a less typical genetic model of resistance was studied in which seedling resistance was activated by an independent locus exhibiting an apparent “nonsuppressing” effect. The knowledge gained by these and other lines of research will contribute to the goal of durable resistance to stem rust.