The effect of VRN1 genes on important agronomic traits in high‐yielding Canadian soft white spring wheat

For reproductive success, flowering time must synchronize with favourable environmental conditions. Vernalization genes play a major role in accelerating or delaying the time to flowering. We studied how different vernalization (VRN1) gene combinations alter days to flowering and maturity and consequently the effect on grain yield and other agronomic traits. The study focussed on the effect of the VRN1 gene series (Vrn‐A1, Vrn‐B1 and Vrn‐D1) and their combinations. The Vrn gene group Vrn‐A1a, Vrn‐B1, vrn‐D1 was the earliest to flower and mature, while Vrn‐A1b, Vrn‐B1, vrn‐D1 was the latest to flower. Spring wheat lines with vrn‐A1, Vrn‐B1, Vrn‐D1 were the highest yielding and matured at a similar time as those having vernalization genes Vrn‐A1a, Vrn‐B1 and Vrn‐D1. The findings of this study suggest that the presence of Vrn‐D1 has a direct or indirect role in producing higher grain yield. We therefore suggest the introduction of Vrn‐D1 allele into higher‐yielding classes within Canadian spring wheat germplasm.     

Evaluation of cold hardiness in two sets of near-isogenic lines of wheat (Triticum aestivum) with polymorphic vernalization alleles

In wheat, variation at the orthologus Vrn‐1 loci, located on each of the three genomes, A, B and D, is responsible for vernalization response. A dominant Vrn‐1a allele on any of the three wheat genomes results in spring habit and the presence of recessive Vrn‐1b alleles on all three genomes results in winter habit. Two sets of near‐isogenic lines (NILs) were evaluated for DNA polymorphisms at their Vrn‐A1, B1 and D1 loci and for cold hardiness. Two winter wheat cultivars, ‘Daws’ and ‘Wanser’ were used as recurrent parents and ‘Triple Dirk’ NILs were used as donor parents for orthologous Vrn‐1 alleles. The NILs were analysed using molecular markers specific for each allele. Only 26 of 32 ‘Daws’ NILs and 23 of 32 ‘Wanser’ NILs had a plant growth habit that corresponded to the marker genotype for the markers used. Freezing tests were conducted in growth chambers programmed to cool to ?21.5°C. Relative area under the death progress curve (AUDPC), with a maximum value of 100 was used as a measure of death due to freezing. The average relative AUDPC of the spring habit ‘Daws’Vrn‐A1a NILs was 86.15; significantly greater than the corresponding winter habit ‘Daws’Vrn‐A1b NILs (42.98). In contrast, all the ‘Daws’Vrn‐A1bVrn‐B1aVrn‐D1b and Vrn‐A1bVrn‐B1bVrn‐D1a NILs (spring habit) had relative AUDPC values equal to those of their ‘Daws’ sister genotypes with Vrn‐A1bVrn‐B1bVrn‐D1b NILs (winter habit). The average AUDPC of spring and winter habit ‘Wanser’ NILs differed at all three Vrn‐A1, Vrn‐B1 and Vrn‐D1 locus comparisons. We conclude that ‘Daws’ and ‘Wanser’ have different background genetic interactions with the Vrn‐1 loci influencing cold hardiness. The marker for Vrn‐A1 is diagnostic for growth habit and cold hardiness but there is no relationship between the Vrn‐B1 and Vrn‐D1 markers and the cold tolerance of the NILs used in this study.     

The influence of photoperiod on the Vrn-H2 locus (4H) which is a major determinant of plant development and reproductive fitness traits in a facultative × winter barley (Hordeum vulgare L.) mapping population

To determine the effect of Vrn‐H2 locus on plant developmental and agronomic traits, detailed controlled environment tests involving a factorial set of vernalization and photoperiod treatments were carried out using doubled haploid lines developed from a facultative (Vrn‐H2^?) × winter (Vrn‐H2⁺) barley cross. The allele phase at the Vrn‐H2 locus influenced heading date as well as the developmental and agronomic traits. The performance of Vrn‐H2⁺ lines was significantly influenced by vernalization: reproductive fitness traits showed significant decreases without vernalization. However, the effects of alleles at the Vrn‐H2 locus extended beyond simple satisfaction of the vernalization requirement. Vrn‐H2⁺ lines showed increased reproductive fitness compared with Vrn‐H2^? lines when vernalization was followed by a long photoperiod. The responses of the two Vrn‐H2 allele classes to photoperiod duration were quite different in terms of heading date, developmental and agronomic traits. These results suggest that alleles at the Vrn‐H2 locus – and/or tightly linked gene(s) – respond primarily to the exogenous signal of vernalization (temperature), but when the vernalization requirement has been fulfilled, they also respond to photoperiod duration.     

Characterization of QEet.ocs-5A.1, a quantitative trait locus for ear emergence time on wheat chromosome 5AL

QEet.ocs‐5A.1, a quantitative trait locus controlling ear emergence time, has been detected on wheat chromosome 5AL using single chromosome recombinant lines (SCRs) developed from a cross between ‘Chinese Spring’ (CS) (‘Cappelle‐Desprez’ 5A) and CS (Triticum spelta 5A). This locus has little influence on grain yield and its components, and thus has breeding potential for changing ear emergence time without yield reduction. To characterize the phenotypic expression of QEet.ocs.1 and to test its interaction with the Vrn‐A1 gene for vernalization response, six near‐isogenic SCRs differing for these two gene regions were grown together with the parental controls under different vernalization and photoperiod regimes. The T. spelta allele of QEet.ocs.1 accelerated heading time when vernalization and photoperiod were satisfied, demonstrating that the function of this QTL is earliness per se. There was no interaction between Vrn‐A1 and QEet.ocs.1.     

Effect of VRN‐1 and PPD‐D1 genes on heading time in European bread wheat cultivars

The variation of the vernalization (VRN‐1) and photoperiod (PPD‐1) genes offers opportunities to adjust heading time and to maximize yield in crop species. The effect of these genes on heading time was studied based on a set of 245 predominantly spring cultivars of bread wheat from the main eco‐geographical regions of Europe. The genotypes were screened using previously published diagnostic molecular markers for detecting the dominant or recessive alleles of the major VRN‐1 loci such as: VRN‐A1, VRN‐B1, VRN‐D1 as well as PPD‐D1. We found that 91% of spring wheat cultivars contain the photoperiod sensitive PPD‐D1b allele. Photoperiod insensitive PPD‐D1a allele has been found mainly in southern region of Europe. For this region the monogenic control of vernalization by VRN‐B1 or VRN‐D1 dominant alleles is common, whereas in the remaining part of Europe, the combination of photoperiod sensitive PPD‐D1b allele with dominant VRN‐A1, VRN‐B1 and recessive vrn‐D1 alleles represents the most frequent genotype. Also, we revealed a significantly later (5–8 days) heading of the monogenically dominant genotypes at VRN‐B1 as compared to the digenic VRN‐A1 VRN‐B1 genotypes.     

Developmental responses to vernalization in wheat deletion lines for chromosomes 5A and 5D

The aim of this investigation was to test the developmental patterns of deletion lines, generated for chromosome arms 5AL and 5DL in the variety ‘Chinese Spring’ (CS) under vernalized and non‐vernalized treatments. Plants were grown in controlled conditions under saturating daylength. Time to heading and the duration of particular phases before flowering were recorded, and leaf and spikelet production rates and numbers were analysed. The lines lacking Vrn‐A1 and Vrn‐D1 were delayed in time to heading under non‐vernalized conditions, because of the lengthening of the emergence to floral initiation phase (EM‐FI) and the terminal spikelet to heading phase (TS‐H). Differences in final leaf numbers corresponded to longer durations of the EM‐FI phase. The absence of Vrn‐A1 and Vrn‐D1 apparently decreased the number of spikelets by a lower primordium production rate, even though the duration of the FI‐TS phase was longer or equal to CS. The sensitivity to vernalization in lines where the Vrn genes were deleted was much higher.     

The influence of a spring habit gene, Vrn-D1, on heading time in wheat

The adaptability of wheat cultivars to environmental conditions is known to be associated with a vernalization requirement, that is, spring/winter habit. To clarify the genetic effect of the spring habit gene, Vrn‐D1, on heading time in the field, recombinant inbred lines (RILs) with or without the Vrn‐D1 gene were produced from F₂ plants of the cross between ‘Nanbukomugi’ and ‘Nishikazekomugi’, non‐carrier and carrier cultivars of this gene, respectively. Using growth chambers with a controlled temperature and photoperiod, three components of heading time, i.e. vernalization requirement, photoperiodic sensitivity and narrow‐sense earliness (earliness per se), were evaluated in each RIL. RILs with the Vrn‐D1 gene (E lines) showed greatly reduced vernalization requirements and slightly shorter narrow‐sense earliness than RILs without Vrn‐D1 (L lines), although no difference in photoperiodic sensitivity was observed between the two groups. RILs were planted at four different sites in Japan and examined for their heading time in the field. E lines headed significantly earlier than L lines at all locations, indicating that the earliness of E lines is stable in various environmental conditions. These results indicated that spring habit caused by Vrn‐D1 gene, as well as narrow‐sense earliness, was responsible for heading time in the field.     

Genetic and Molecular Characterization of Vernalization Genes Vrn‐A1, Vrn‐B1, and Vrn‐D1 in Spring Wheat Germplasm from the Pacific Northwest Region of the U.S.A.

The objective of this study was to determine the Vrn‐1 allelic composition of spring wheat germplasm from the Pacific Northwest region of the USA. Individual plants from 56 spring wheat lines were crossed to near‐isogenic tester lines carrying the dominant allele Vrn‐A1, Vrn‐B1 or Vrn‐D1. F₂ progeny were evaluated for growth habit in the field and Vrn‐1 allelic composition was determined through chi‐square analysis. Lines also were analysed with DNA sequence‐based Vrn‐1 allele‐specific markers. A majority of the germplasm carried the dominant allele Vrn‐A1a alone or in combination with Vrn‐B1, Vrn‐D1 or Vrn‐B3 alleles. Vrn‐B1 and Vrn‐D1 were almost always associated with other dominant Vrn‐1 allele(s). Based on DNA sequence analysis, a novel Vrn‐B1 allele referred to as Vrn‐B1b, which carried a single nucleotide polymorphism (SNP) and a 36 bp deletion, was identified in cultivar ‘Alpowa’. These results will be useful to wheat breeders for choosing parents with different Vrn‐1 alleles for crossing to maximize diversity at the Vrn‐1 loci with an expectation of identifying superior Vrn‐1 allelic combinations for cultivar improvement.     

Mapping of the Vrn-B1 gene in Triticum aestivum using microsatellite markers

An F₂ population segregating for the dominant gene Vrn‐B1 was developed from the cross of the substitution line ‘Diamant/'Miro‐novskaya 808 5A’ and the winter wheat cultivar ‘Bezostaya 1′. Microsatellite markers (Xgwm and Xbarc) with known map locations on chromosome 5B of common wheat were used for mapping the gene Vrn‐B1. Polymorphism between parental varieties was observed for 28 out of 34 microsatellite markers (82%). Applying the quantitative trait loci mapping approach, the target gene was mapped on the long arm of chromosome 5B, closely linked to Xgwm408. The map position of Vrn‐B1 suggests that the gene is homoeologous to other vernalization response genes located on the homoeologous group 5 chromosomes of wheat, rye and barley.     

普通小麦春化基因VRN1 RNA干扰载体构建及转基因小麦获得

为进一步探究春化基因VRN1在小麦发育进程中的功能,利用荧光定量PCR分析了VRN1基因在不同发育特性小麦品种新春2号、京841中的表达情况。结果表明,随着生育进程的推进,VRN1基因在新春2号叶片和茎尖中表达量均呈上升趋势,VRN1基因在京841叶片中呈波动上升趋势,在茎尖中表达量趋于0;以p FGC5941载体为基础构建含有VRN1反向重复序列的RNA干扰载体,利用农杆菌介导的茎尖转化法转化新春2号获得了再生植株,并通过PCR法检测获得了转基因阳性植株,为从分子水平上实现小麦发育特性遗传改良和创育小麦新种质奠定了基础。     

Comparative mapping and its use for the genetic analysis of agronomic characters in wheat

Summary The advent of molecular marker systems has made it possible to develop comparative genetic maps of the genomes of related species in the Triticeae. These maps are being applied to locate and evaluate allelic and homoeoallelic variation for major genes and quantitative trait loci within wheat, and to establish the pleiotropic effects of genes. Additionally, the known locations of genes in related species can direct searches for homoeologous variation in wheat and thus facilitate the identification of new genes. Examples of such analyses include the validation of the effects of Vrn1 on chromosome 5A on flowering time in different crosses within wheat; the indication of pleiotropic effects for stress responses by the Fr1 locus on chromosome 5A; the detection of homoeologous variation for protein content on the homoeologous Group 5 chromosomes; and the detection of a new photoperiod response gene Ppd-H1 in barley from homoeology with Ppd2 of wheat.     

Waxy proteins in diploid, tetraploid and hexaploid wheats

Electrophoretic analyses of waxy proteins, encoded by genes present at the Wx‐1 loci, present in several cultivars and accessions of hexaploid wheat, Triticum aestivum, have permitted the detection of null alleles at the Wx‐B1 and Wx‐D1 loci. Polymorphism at the Wx‐A1 and Wx‐B1 loci was also investigated in several accessions of tetraploid wheats, Triticum durum, Triticum dicoccoides and Triticum timopheevi, and in diploid species, Triticum urartu, Triticum boeoticum and Triticum monococcum. One null allele at the Wx‐A1 locus and three polymorphic alleles at Wx‐B1 locus were detected in T. durum; a new allele at one of the two waxy loci was identified in the tetraploid wheat T. timopheevi; no polymorphism was detected in diploid species. Polymerase chain reaction techniques made possible the detection of further polymorphism existing at the Wx‐1 loci and the reason for the lack of expression of the null genotypes to be investigated. The null forms detected at each locus have been used to produce complete sets of partial and total waxy lines in durum and bread wheat.     

Analysis of D-prolamins synthesized by the Hordeum chilense genome and their effects on gluten strength in hexaploid tritordeum

Hexaploid tritordeum is the amphiploid derived from the cross between Hordeum chilense and durum wheat. The storage proteins synthesized in the H^ch genome influence the gluten strength of this amphiploid. The D‐prolamins of H. chilense have been analysed by sodium dodecyl sulphate‐polyacrylamide gel electrophoresis with and without urea. A new locus named Glu‐H^ch3 has been detected. The effects of allelic variation at this locus on gluten strength, as measured the sodium dodecyl sulphate sedimentation test, were determined using seeds of 92 lines from a cross of two hexaploid tritordeum lines. Two allelic variants have been detected for this locus, which have shown different effects on gluten strength.     

Polymorphism of waxy proteins in Spanish durum wheats

A collection of 547 durum wheats (103 cultivars and 444 landraces) from Spain was analysed for waxy protein composition. The electrophoretic patterns showed low polymorphism. At the Wx‐A1 locus, 99.8% of the wheats had the Wx‐Ala allele and only one had the null Wx‐Alb allele. The Wx‐Bl locus was more polymorphic and four different alleles were detected: Wx‐Bla (41.3%), Wx‐Blc (42.6%), a new allele, not detected before in bread wheat and named Wx‐Blf (16.0%), and the null Wx‐Blb allele, found for the first time in one durum wheat. Eleven durum wheats with different allelic composition at the Wx‐l loci were analysed for amylose content. Wheats with the Wx‐Bla allele had a lower amylose content than those with Wx‐Blc or Wx‐Blf. The lowest amylase content was found in the only durum wheat having the null Wx‐Blb allele.     

小麦TaFT基因编码区序列多态性及其与开花期的关系

春化基因VRN-B3是小麦开花素基因TaFT,为探索该基因在品种间的保守性及其与小麦开花早晚的关系,根据TaFT基因序列(GenBank accession No.: DQ890162)设计特异PCR引物,扩增了13个品种中该基因的编码区。通过测序和序列比对,发现不同品种间该基因编码区的DNA序列存在多态性,序列翻译发现5个品种的表达产物FT蛋白发生变异。利用中国春的非整倍体材料将TaFT基因定位在7BS染色体上。参考品种的冬春性及开花时间,推测冬性品种正常的FT蛋白(同DQ890162翻译的氨基酸序列一致)可加速开花,FT蛋白变异则延迟开花;春性品种的FT蛋白变异与否对开花期影响不大,推测TaFT基因的效应可能被春性品种的显性春化基因所掩盖。     

Location of a gene for frost resistance on chromosome 5A of wheat

Summary A gene for frost resistance on chromosome 5A of wheat was located using single chromosome recombinant lines from the cross between the substitution line Hobbit (Triticum spelta 5A) and Hobbit. In this sample of recombinant lines the locus for frost resistance, designated Fr1, is completely linked to the locus Vrn1 controlling vernalisation requirement. The results can be explained by a pleiotropic action of the Vrn1 locus or close genetic linkage between Vrn1 and Fr1. Further detailed study is necessary to resolve these alternative hypotheses.     

Adaptation and ecological differentiation in wheat with special reference to geographical variation of growth habit and Vrn genotype

Geographical variation of growth habit was studied for 749 landraces from various parts of the world, with special reference to their adaptation and ecogeographical differentiation. The total frequency of spring‐type landraces was 49.9%, and varied between localities. Spring‐type landraces were frequent in two distinct areas where the average January temperature was either below ‐7°C or above 4°C, with winter‐type landraces in areas from ‐7°C to 4°C. These results indicated that geographical variation of growth habit is closely related to the degree of winter coldness. An analysis of the Vrn genotype for 216 spring‐type landraces demonstrated the uneven distribution of four Vrn genes, with Vrn4 being the least frequent. The adaptive Vrn genotype was different between localities. Genotypes carrying Vrn‐A1 and additional Vrn gene(s) were frequent in two distinct areas where the average January temperature was either below ‐7°C or over 10°C, while genotypes with any of three Vrn genes, except Vrn‐A1, adapted to areas with temperatures from 4°C to 10°C. Therefore, it was concluded that the adaptability of wheat landraces differed depending on their growth habit and Vrn genotype, and that ecotypes with different Vrn genotypes were allopatrically distributed as a result of adaptation to different winter temperature. However, the differential distribution of Vrn‐B1, Vrn‐D1 and Vrn4 could not be explained by their adaptability, and might reflect the polyphyletic origin of common wheat.     

等位变异Vrn-B1a和Vrn-B1b的春化效应及其在黄淮冬麦区小麦品种中的分布

春化基因Vrn-B1是决定黄淮冬麦区小麦品种冬春性的主要基因之一, 研究其不同显性等位变异的低温春化作用效应及分布, 对该区小麦品种选育和推广具有重要意义。以等位变异Vrn-B1a品种皖麦33与等位变异Vrn-B1b品种豫麦34为亲本构建杂交组合, 对其F₂代进行5~35 d的低温春化处理, 并在温室(22±3℃,16 h昼/8 h夜)鉴定抽穗期, 结合分子标记分析低温春化处理时间对各等位变异型抽穗期的影响。同时对228个黄淮冬麦区小麦品种进行相关位点分子检测, 分析该基因等位变异的分布特点。各春化处理均使两种等位变异小麦植株的抽穗期提前, 但Vrn-B1a抽穗时间比Vrn-B1b晚约2 d。从春化处理当天至处理后25 d, 2种等位变异类型的抽穗时间均随春化时间的延长而缩短; 继续延长春化时间, 抽穗期不再缩短, 表明满足两种等位变异完成春化的低温时间为20~25 d。在228个品种中, Vrn-B1位点有214个(93.9%)隐性和14个(6.1%)显性等位变异。其中, 显性等位变异Vrn-B1a有6个, 占总品种数的2.6%; Vrn-B1b有8个, 占总品种数的3.5%。在黄淮冬麦区小麦品种中, 春化基因Vrn-B1位点至少存在Vrn-B1a和Vrn-B1b两种显性等位变异类型, 两种等位变异类型纯合小麦植株的抽穗时间不同。     

Natural variation in photoperiodic flowering pathway and identification of photoperiod-insensitive accessions in wild wheat, <Emphasis Type="Italic">Aegilops tauschii</Emphasis>

The D-genome progenitor of hexaploid wheat, Aegilops tauschii Coss., has a wide natural species range in central Eurasia and possesses wide natural variation in heading and flowering time. Here, we report identification of two Ae. tauschii accessions insensitive to short day length. Similarly to a loss or reduced degree of vernalization requirement, the photoperiod-insensitive mutations were found only in the early flowering sublineage (TauL1b) of Ae. tauschii. Quantitative trait locus (QTL) analyses using two F₂ mapping populations showed that a QTL for heading time on the long arm of chromosome 5D was related to the early heading phenotype of the photoperiod-insensitive accessions under short-day conditions. In the photoperiod-insensitive accession, expression patterns of two flowering-related genes were altered under short-day conditions compared with the patterns in photoperiod-sensitive accessions. This study indicates that analysis of natural variations in the Ae. tauschii population is useful to find novel genetic loci controlling agronomically important traits.