Molecular aspects of sucrose transport and its metabolism to starch during seed development in wheat: A comprehensive review

Wheat is one of the most important crops globally, and its grain is mainly used for human food, accounting for 20% of the total dietary calories. It is also used as animal feed and as a raw material for a variety of non-food and non-feed industrial products such as a feedstock for the production of bioethanol. Starch is the major constituent of a wheat grain, as a result, it is considered as a critical determinant of wheat yield and quality. The amount and composition of starch deposited in wheat grains is controlled primarily by sucrose transport from source tissues to the grain and its conversion to starch. Therefore, elucidation of the molecular mechanisms regulating these physiological processes provides important opportunities to improve wheat starch yield and quality through biotechnological approaches. This review comprehensively discusses the current understanding of the molecular aspects of sucrose transport and sucrose-to-starch metabolism in wheat grains. It also highlights the advances and prospects of starch biotechnology in wheat.     

Interspecific and intergeneric hybridization as a source of variation for wheat grain quality improvement

Key message

The hybridization events with wild relatives and old varieties are an alternative source for enlarging the wheat quality variability. This review describes these process and their effects on the technological and nutritional quality.

Abstract

Wheat quality and its end-uses are mainly based on variation in three traits: grain hardness, gluten quality and starch. In recent times, the importance of nutritional quality and health-related aspects has increased the range of these traits with the inclusion of other grain components such as vitamins, fibre and micronutrients. One option to enlarge the genetic variability in wheat for all these components has been the use of wild relatives, together with underutilised or neglected wheat varieties or species. In the current review, we summarise the role of each grain component in relation to grain quality, their variation in modern wheat and the alternative sources in which wheat breeders have found novel variation.

     

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.     

Chromosomes 3B and 4D are associated with several milling and baking quality traits in a soft white spring wheat (<Emphasis Type="Italic">Triticum aestivum</Emphasis> L.) population

Wheat is marketed based on end-use quality characteristics and better knowledge of the underlying genetics of specific quality parameters is essential to enhance the breeding process. A set of 188 recombinant inbred lines from a ‘Louise’ by ‘Penawawa’ mapping population was grown in two crop years at two locations in the Pacific Northwest region of the United States and data were collected on 17 end-use quality traits using established quality analysis protocols. Using an established genetic linkage map, composite interval mapping was used to identify QTL associated with 16 of the 17 quality traits. QTL were found on 13 of the 21 wheat chromosomes. A large number of QTL were located on chromosomes 3B and 4D and coincided with traits for milling quality and starch functionality. Chromosome 3B contained 10 QTL, which were localized to a 26.2 cM region. Chromosome 4D contained 7 QTL, all of which were located on an 18.8 cM region of this chromosome. The majority of the alleles for superior end-use quality were associated with the cultivar Louise. The identified QTL detected remained highly significant independent of grain yield and protein quantity. The identification of these QTL for end-use quality gives key insight into the relationship and complexity of end-use quality traits. It also improves our understanding of these relationships, thereby allowing plant breeders to make valuable gains from selection for these important traits.     

小麦低分子量麦谷蛋白亚基功能标记研究进展

小麦是我国主要的粮食作物之一,籽粒中的低分子量麦谷蛋白对于小麦面包的加工品质具有重要的作用。近年来,利用分子标记技术检测小麦低分子量麦谷蛋白亚基（low molecular weight glutenin subunit,LMW-GS）的类型和组成已成为小麦品质改良的研究热点之一。主要综述了小麦低分子量麦谷蛋白亚基基因和蛋白质的结构特征、分类以及功能标记的研究进展,讨论了开发利用小麦Glu-A3、Glu-B3、Glu-D3位点LMW-GS功能标记的意义及存在的问题,并强调了LMW-GS分子标记检测技术的革新及亚基类型的完善对小麦品质改良的重要性,以期加速LMW-GS功能标记在优质小麦育种工作中的应用进程。     

基因型与生态环境对小麦籽粒品质与蛋白质组分的影响

通过2年3点试验,研究了40个小麦(Triticum aestivum)品种(品系)籽粒品质性状和蛋白质组分含量的变异。结果表明,籽粒品质和蛋白质组分在基因型间存在较大的差异;根据小麦籽粒品质的综合性状,可将40个小麦品种(品系)分为6组不同的品质类型,在本试验点的生态环境条件下。基本以中筋及弱筋小麦为主;生态环境对小麦籽粒的容重、沉降值、湿面筋含量、蛋白质含量、赖氨酸含量与蛋白质组分含量均有极显著的影响,而面筋指数、淀粉含量和直链淀粉含量对环境反应不敏感,适宜的生态环境条件有利于形成合理的谷蛋白／醇溶蛋白比。面粉面筋质量好,基因型与生态环境的互作对小麦籽粒品质。谷蛋白与醇溶蛋白及两者的比值有显著影响,对球蛋白影响不大,而面粉蛋白质含量、面筋含量、沉降值及千粒重主要受基因的表达和环境的独立影响,蛋白质组分含量在基因型间和环境间的变化与小麦籽粒烘烤品质密切相关。     

Profiling the Expression of Genes Controlling Rice Grain Quality

Rice provides a staple source of energy, protein and other nutrients to half of the world population. Over 90 of the rice seeds consists of starch and protein by dry weight. The quantity and property of starch and protein thus play a dominant role in the yield and quality of rice. The amylase content of starch is a determining factor in the eating and cooking quality while the amount and essential amino acids balance of storage proteins affect the nutritional quality of rice. In China, the super-hybrid rice currently under the last phase of development has a 35 yield advantage over the best inbred rice varieties. However, its grain quality needs further improvement. This study reported the expression patterns of 44 genes participating in starch, storage protein, and lysine synthesis in the developing rice grain. Field grown rice cultivar 9311, the paternal line of an elite super-hybrid rice LYP9with its draft genomic sequence released, was used as plant material. Results revealed diverse yet coordinated expression profiles of the genes involved in the three pathways which lead to the final composition and property of starch, protein and lysine that determine the quality of rice, providing useful information for rice quality improvement.     

不同氮肥基追比例对高温胁迫下小麦籽粒产量和品质的影响

选用强筋小麦品种济麦20、烟农19、藁麦8901做试验材料,设置不同氮肥基追比例和籽粒灌浆中后期高温胁迫处理,研究了不同氮肥基追比例对高温胁迫条件下小麦籽粒产量和品质的影响.研究结果表明,追氮比例由50%增加到70%,3个品种的千粒重、籽粒产量、粗蛋白含量、湿面筋含量、醇溶蛋白含量、谷蛋白含量、HMW-GS含量、LMW-GS含量、HMW-GS/LMW-GS比值显著提高.济麦20和烟农19的谷蛋白大聚合体含量、谷蛋白大聚合体体积加权平均粒径和表面积加权平均粒径因追氮比例提高而升高, 藁麦8901则无显著变化.济麦20和烟农19的面团形成时间、面团稳定时间因追氮比例提高而延长, 藁麦8901基本不受影响.追氮比例由50%增加到70%,3个品种的籽粒支链淀粉/直链淀粉比值显著降低,淀粉糊化高峰黏度、低谷黏度、稀懈值、最终黏度和反弹值相应降低.总之,提高氮肥追施比例可在一定程度上缓解灌浆期高温胁迫对小麦粒重和蛋白质质量的不利影响,但对淀粉质量产生负面效应,且品种间存在差异.     

Combining mutations at genes encoding key enzymes involved in starch synthesis affects the amylose content,carbohydrate allocation and hardness in the wheat grain

Modifications to the composition of starch, the major component of wheat flour, can have a profound effect on the nutritional and technological characteristics of the flour's end products. The starch synthesized in the grain of conventional wheats (Triticum aestivum) is a 3:1 mixture of the two polysaccharides amylopectin and amylose. Altering the activity of certain key starch synthesis enzymes (GBSSI, SSIIa and SBEIIa) has succeeded in generating starches containing a different polysaccharide ratio. Here, mutagenesis, followed by a conventional marker‐assisted breeding exercise, has been used to generate three mutant lines that produce starch with an amylose contents of 0%, 46% and 79%. The direct and pleiotropic effects of the multiple mutation lines were identified at both the biochemical and molecular levels. Both the structure and composition of the starch were materially altered, changes which affected the functionality of the starch. An analysis of sugar and nonstarch polysaccharide content in the endosperm suggested an impact of the mutations on the carbon allocation process, suggesting the existence of cross‐talk between the starch and carbohydrate synthesis pathways.     

花后干旱和渍水对不同品质类型小麦籽粒品质形成的影响

 防雨池栽条件下研究了花后干旱和渍水胁迫对两个不同品质类型小麦（Triticum aestivum）品种籽粒产量和品质形成的影响。结果表明,花后渍水和干旱处理明显降低了小麦籽粒产量和蛋白质产量。在整个灌浆期内干旱处理明显提高了籽粒蛋白质和醇溶蛋白含量,而渍水处理降低了籽粒蛋白质及其组分的积累量。籽粒总淀粉和直链淀粉含量以渍水处理最高,而支链淀粉以对照最高。干旱处理提高了籽粒干、湿面筋含量、沉降值和降落值,而渍水处理降低了上述品质指标。试验表明干旱和渍水胁迫对小麦籽粒蛋白质与淀粉的含量和组分及面粉品质等均有不同程度的影响,从而改变了不同品质类型小麦的籽粒品质。     

Opportunities for manipulating the seed protein composition of wheat and barley in order to improve quality

Wheat and barley are the major temperate cereals, being used for food, feed and industrial raw material. However, in all cases the quality may be limited by the amount, composition and properties of the grain storage proteins. We describe how a combination of biochemical and molecular studies has led to an understanding of the molecular basis for breadmaking quality in wheat and feed quality in barley, and also provided genes encoding key proteins that determine quality. The control of expression of these genes has been studied in transgenic tobacco plants and by transient expression in cereal protoplasts, providing the basis for the production of transgenic cereals with improved quality characteristics.     

根部喷施FeSO_4对春小麦籽粒组分和面粉品质的影响

以4个春小麦品种为材料,在温室条件下研究了根部喷施不同量FeSO4对小麦籽粒硫含量、铁含量、蛋白质含量、淀粉组成、SDS沉淀值、面筋品质和面团流变学特性的影响.结果表明:喷施FeSO4后4个品种的硫含量、铁含量、蛋白含量、SDS沉淀值、湿面筋含量和面筋指数均显著高于对照,但各处理间干面筋含量无显著变化,且不同品种、不同品质参数达到最高值的FeSO4喷施量并不一致;2个品种的直链淀粉含量、直支比和总淀粉含量比对照显著降低,另2个品种直链淀粉含量和直支比却无显著变化;各品种的面团形成时间、稳定时间和断裂时间随着FeSO4喷施量的增加呈现出先升高后降低的趋势,并均在15 g/m2或22.5 g/m2 FeSO4喷施量水平达到最佳,但均与FeSO4喷施量无显著相关性.研究发现,根部喷施适宜浓度的FeSO4可在一定程度上改善春小麦籽粒组分和面粉品质,但改善的效果因品种和品质参数而异.     

Genetic diversity of bread wheat genotypes in Iran for some nutritional value and baking quality traits

Genetic variation among 78 irrigated bread wheat genotypes was studied for their nutritional value and baking quality traits as well as some agronomic traits. The experiment was conducted in a randomized complete block design with three replicates under normal and terminal drought stress conditions in Kermanshah, Iran during 2012–2013 cropping season. The results of combined ANOVA indicated highly significant genotypic differences for all traits. All studied traits except grain yield, hectoliter weight and grain fiber content were significantly affected by genotype × environment interaction. Drought stress reduced grain yield, thousand kernel weight, gluten index, grain starch content and hectoliter weight and slightly promoted grain protein and fiber contents, falling number, total gluten and ratio of wet gluten to grain protein content. Grain yield by 31.66% and falling number by 9.20% attained the highest decrease and increase due to drought stress. There were negative and significant correlations among grain yield with grain protein and fiber contents under both conditions. Results of cluster analysis showed that newer genotypes had more grain yield and gluten index than older ones, but instead, they had the lower grain protein and fiber contents. It is thought that wheat breeders have bred cultivars with high grain yield, low protein content, and improved bread-making attributes during last seven decades. While older genotypes indicated significantly higher protein contents, and some of them had higher gluten index. We concluded from this study that it is imperative for breeders to pay more attention to improve qualitative traits coordinated to grain yield.     

基因枪法转化小麦谷蛋白基因研究进展

小麦面粉品质的优劣主要取决于麦谷蛋白多聚体结构的组成,谷蛋白多聚体由高分子量谷蛋白亚基(HMW-GS)、低分子量谷蛋白亚基(LMW-GS)和醇溶蛋白以二硫键相互交联构成,其数量和结构特征直接影响面团的粘弹性,所以通过基因工程方法转化优质谷蛋白基因,增加谷蛋白数量,改善谷蛋白多聚体结构组成,进而改良面粉品质的研究逐渐引起国内外的重视,并在近年来取得了重要进展。基因枪法是目前利用基因工程改良小麦品质的主要途径,自1992年以来已在多个研究室取得了较为瞩目的成果,显示了基因工程改良小麦品质的可能性及前景。综述了迄今为止国内外利用基因枪法转化谷蛋白基因改良小麦品质的研究进展,并在受体材料的选择等方面的研究现状作了较为详细的阐述。     

四川省的小麦地方品种品质分析

以67份四川省的小麦地方品种为试验材料,测定其19个品质指标并进行品质评价,旨在为小麦品质改良提供信息。结果表明,蛋白质和赖氨酸含量偏低,湿面筋含量、沉降值和面筋指数较高。粉质仪参数——形成时间、稳定时间和评价值偏低,面团流变学特性差。但也发现一些优质或专用小麦材料,如蛋白质含量〉14％的1份,湿面筋含量〉40％的10份,沉降值〉40ml的29份,中筋和弱筋小麦分别为7份和5份,德阳天绿场小麦、南部棒槌麦、酉阳光头、安岳红小麦和蓬溪红花光头麦5份材料具有相对较好的综合品质。相关分析表明,蛋白质含量、干湿面筋含量、沉降值、形成时间、稳定时间和评价值两两问简单相关（极）显著,蛋白质含量与湿面筋含量间和沉降值与稳定时间间偏相关显著。蛋白质含量与总淀粉含量间简单相关为极显著负相关。偏相关不显著。总淀粉含量与支链淀粉含量问简单相关和偏相关均极显著,总淀粉含量与直链淀粉含量间简单相关不显著,偏相关极显著,直链淀粉含量与支链淀粉含量间简单相关和偏相关均为极显著负相关。因此,在小麦育种早代进行蛋白质含量、沉降值和直链淀粉含量的选择为好。     

Molecular characterization and functional analysis of elite genes in wheat and its related species

The tribe Triticeae includes major cereal crops (bread wheat, durum wheat, triticale, barley and rye), as well as abundant forage and lawn grasses. Wheat and its wild related species possess numerous favourable genes for yield improvement, grain quality enhancement, biotic and abiotic stress resistance, and constitute a giant gene pool for wheat improvement. In recent years, significant progress on molecular characterization and functional analysis of elite genes in wheat and its related species have been achieved. In this paper, we review the cloned functional genes correlated with grain quality, biotic and abiotic stress resistance, photosystem and nutrition utilization in wheat and its related species.     

不同生态环境与播种期下小麦籽粒品质变异规律的研究

选用 6个不同品质类型小麦品种在 4个生态点进行分期播种试验, 系统分析了不同生态环境下小麦籽粒产量与品质的变异特征及其与主要气候生态因子间的关系。结果表明 :生态点、品种以及地点×品种互作对籽粒产量、千粒重、蛋白质、湿面筋和淀粉含量、沉降值与降落值的影响均达到显著水平 ;不同播种期处理对产量与淀粉含量的影响达到极显著水平, 而播种期×品种互作对千粒重、降落值、淀粉含量及沉降值的效应达到显著水平 ;地点×播种期×品种互作仅对产量、湿面筋、淀粉含量与沉降值有显著的影响。在 4个不同生态点中, 南京点的籽粒蛋白质与湿面筋含量最低, 但淀粉含量最高 ;徐州点的产量和千粒重最大 ;泰安点的蛋白质含量与湿面筋含量最高, 沉降值最小 ;保定点的产量、千粒重最小, 但沉降值最大。不同播种期处理下, 适播与晚播的籽粒蛋白质含量、湿面筋含量、淀粉含量、沉降值与降落值都显著高于早播, 而早播期的产量和千粒重最大。各小麦品种在不同地点与播种期下产量与品质性状的变异中以降落值的变异系数为最大, 淀粉的变异为最小。开花至成熟期的日均温与淀粉含量呈线性负相关, 与产量、蛋白质和湿面筋含量及降落值呈二次曲线相关关系 ;日温差与产量和千粒重呈二次曲线相关关系, 籽粒蛋白质和湿面筋含量、沉降值及降落值则随昼温差的增加线性递增 ;开花至成熟期降雨量与产量、千粒重都呈现先升后降的二次曲线相关关系, 而与籽粒蛋白质含量和降落值呈现线性负相关关系 ;籽粒蛋白质和湿面筋含量与降落值随开花至成熟期的累计日照时数呈现线性正相关关系。     

Novel and favorable QTL allele clusters for end-use quality revealed by introgression lines derived from synthetic wheat

Wheat quality is an important target trait. Previous studies mainly focus on storage protein, but their contribution to quality is partial, and most loci for quality are still undetected. Wild species of wheat are valuable resources for wheat improvement and introgression lines (ILs) are the ideal materials for detecting quantitative trait loci (QTL). In this study, a set of 82 BC5 F2-6 ILs, carrying a range of introgressed chromosome segments from a synthetic hexaploid wheat Am3 (Triticum carthlicum × Aegilops tauschii), was developed and genotyped with 170 microsatellite markers. QTL analysis was performed for 14 parameters, sodium dodecyl sulfate sedimentation volume, grain protein content (GPC), grain hardness and 11 mixograph parameters, associated with end-use quality of wheat, using the materials harvested in three environments. This led to the detection of 116 QTL, with c. 95% of the positive alleles contributed by Am3. Six important and novel genomic regions for bread-making quality were found on chromosomes 2D, 3A, 4A, 4B, 5A and 6A. These loci for bread-making quality showed pleiotropy and had large positive effects on several quality parameters with no or very weak negative effect on grain yield, thus demonstrating the value of synthetic wheat as a source of useful genetic variation for the improvement of bread wheat quality.     

烯效唑干拌种对小麦氮素积累和运转及籽粒蛋白质品质的影响

通过田间试验,研究了不同烯效唑干拌种剂量对3个不同筋力小麦品种植株氮素积累、运转和籽粒蛋白质品质的影响,结果表明,基因型、环境及烯效唑处理对小麦品质的影响效应依次减小,且均达到了极显著水平,但三者的互作效应较小。烯效唑处理后提高了不同生态点下不同小麦品种籽粒蛋白质含量和产量,处理后的面筋含量和沉淀值增加,面团形成时间和稳定时间延长;干拌种增加了开花期各营养器官中的氮素含量和单株氮素积累量,花后氮素总转移量、总转移率及其对籽粒氮的贡献率极显著提高,且处理后旗叶中可溶性蛋白质含量在花后15 d内均显著高于对照;对籽粒中氮含量而言,烯效唑处理后提高了灌浆初期籽粒中的非蛋白氮含量,花后5—20 d内均高于对照,灌浆期间籽粒蛋白氮含量均高于对照,因而处理后的粗蛋白质含量变化动态特点为谷底高、回升快。研究认为,烯效唑处理如同基因、环境一样独立影响小麦籽粒品质,而烯效唑处理后提高了开花初期旗叶中的可溶性蛋白质含量和花前营养器官中氮素含量及花后氮素转运量,可能是其提高籽粒非蛋白氮含量、促进籽粒蛋白质含量增加和蛋白质质量提高的重要原因之一,烯效唑干拌种对小麦籽粒蛋白质品质的改善具有广适性。