Mapping of powdery mildew resistance genes transferred to common wheat from wild emmer wheat revealed three functional Pm60 haplotypes

Powdery mildew(PM),caused by Blumeria graminis f.sp.tritici(Bgt),is one of the destructive wheat diseases worldwide.Wild emmer wheat(Triticum turgidum ssp.dicoccoides,WEW),a tetraploid progenitor of common wheat,is a valuable genetic resource for wheat disease resistance breeding programs.We developed three hexaploid pre-breeding lines with PM resistance genes derived from three WEW accessions.These resistant pre-breeding lines were crossed with susceptible common wheat accessions.Segregations in the F2populations were 3 resistant:1 susceptible,suggesting a single dominant allele in each resistant parent.Mapping of the resistance gene in each line indicated a single locus on the long arm of chromosome 7A,at the approximate location of previously cloned Pm60 from T.urartu.Sanger sequencing revealed three different Pm60 haplotypes(Hap 3,Hap 5,and Hap 6).Co-segregating diagnostic markers were developed for identification and selection of each haplotype.The resistance function of each haplotype was verified by the virus-induced gene silencing(VIGS).Common wheat lines carrying each of these Pm60 haplotypes were resistant to most Bgt isolates and differences in the response arrays suggested allelic variation in response.

Genetic improvement of heat tolerance in wheat:Recent progress in understanding the underlying molecular mechanisms

As a cool season crop, wheat(Triticum aestivum L.) has an optimal daytime growing temperature of 15 ℃ during the reproductive stage. With global climate change, heat stress is becoming an increasingly severe constraint on wheat production. In this review, we summarize recent progress in understanding the molecular mechanisms of heat tolerance in wheat. We firstly describe the impact of heat tolerance on morphology and physiology and its potential effect on agronomic traits. We then review recent discoveries in determining the genetic and molecular factors affecting heat tolerance, including the effects of phytohormone signaling and epigenetic regulation. Finally, we discuss integrative strategies to improve heat tolerance by utilization of existing germplasm including modern cultivars, landraces and related species.

Characterization of a new hexaploid triticale 6D(6A) substitution line with increased grain weight and decreased spikelet number

Hexaploid triticale(×Triticosecale,AABBRR)is an important forage crop and a promising energy plant.Transferring D-genome chromosomes or segments from common wheat(Triticum aestivum)into hexaploid triticale is attractive in improving its economically important traits.Here,a hexaploid triticale 6D(6A)substitution line Lin 456 derived from the cross between the octoploid triticale line H400 and the hexaploid wheat Lin 56 was identified and analyzed by genomic in situ hybridization(GISH),fluorescence in situ hybridization(FISH),and molecular markers.The GISH analysis showed that Lin 456 is a hexaploid triticalewith 14 rye(Secale cereale)chromosomes and 28 wheat chromosomes,whereas non-denaturing fluorescence in situ hybridization(ND-FISH)and molecular marker analysis revealed that it is a 6D(6A)substitution line.In contrast to previous studies,the signal of Oligo-pSc119.2 was observed at the distal end of 6DL in Lin 456.The wheat chromosome 6D was associatedwith increased grain weight and decreased spikelet number using the genotypic data combined with the phenotypes of the F2 population in the three environments.The thousand-grain weight and grain width in the substitution individuals were significantly higher than those in the non-substitution individuals in the F2 population across the three environments.We propose that the hexaploid triticale 6D(6A)substitution line Lin 456 can be a valuable and promising donor stock for genetic improvement during triticale breeding.

Genome-wide linkage mapping of QTL for root hair length in a Chinese common wheat population

Root hairs are fast growing,ephemeral tubular extensions of the root epidermis that aid nutrient and water uptake.The aim of the present study was to identify QTL for root hair length(RHL)using 227 F8 recombinant inbred lines(RILs)derived from a cross of Zhou 8425 B(Z8425 B)and Chinese Spring(CS),and to develop convenient molecular markers for markerassisted breeding in wheat.Analysis of variance of root hair length showed significant differences(P<0.01)among RILs.The genetic map for QTL analysis consisted of 3389 unique SNP markers.Using composite interval mapping,four major QTL(LOD>2.5)for RHL were identified on chromosomes 1 B(2),2 D and 6 D and four putative QTL(2≤LOD≤2.5)were detected on chromosomes 1 A,3 A,6 B,and 7 B,explaining 3.32%–6.52%of the phenotypic variance.The positive alleles for increased RHL of QTL on chromosomes 2 D,6 B and 6 D(QRhl.cau-2 D,q Rhl.cau-6 B,and QRhl.cau-6 D)were contributed by Z8425 B,and CS contributed positive QTL alleles on chromosomes 1 A(q Rhl.cau-1 A),1 B(QRhl.cau-1 B.1 and QRhl.cau-1 B.2),3 A(q Rhl.cau-3 A)and 7 B(q Rhl.cau-7 B).STARP markers were developed for QRhl.cau-1 B.1,QRhl.cau-2 D,QRhl.cau-6 D,and q Rhl.cau-7 B.Haplotype and association analysis indicated that the positive allele of QRhl.cau-6 D had been strongly selected in Chinese wheat breeding programs.Collectively,the identified QTL for root hair length are likely to be useful for marker-assisted selection.

A wheat integrative regulatory network from large-scale complementary functional datasets enables trait-associated gene discovery for crop improvement

Gene regulation is central to all aspects of organism growth,and understanding it using large-scale functional datasets can provide a whole view of biological processes controlling complex phenotypic traits in crops.However,the connection between massive functional datasets and trait-associated gene discovery for crop improvement is still lacking.In this study,we constructed a wheat integrative gene regulatory network(wGRN)by combining an updated genome annotation and diverse complementary functional datasets,including gene expression,sequence motif,transcription factor(TF)binding,chromatin accessibility,and evolutionarily conserved regulation.wGRN contains 7.2 million genome-wide interactions covering 5947 TFs and 127439 target genes,which were further verified using known regulatory relationships,condition-specific expression,gene functional information,and experiments.We used wGRN to assign genome-wide genes to 3891 specific biological pathways and accurately prioritize candidate genes associated with complex phenotypic traits in genome-wide association studies.In addition,wGRN was used to enhance the interpretation of a spike temporal transcriptome dataset to construct high-resolution networks.We further unveiled novel regulators that enhance the power of spike phenotypic trait prediction using machine learning and contribute to the spike phenotypic differences among modern wheat accessions.Finally,we developed an interactive webserver,wGRN(http://wheat.cau.edu.cn/wGRN),for the community to explore gene regulation and discover trait-associated genes.Collectively,this community resource establishes the foundation for using large-scale functional datasets to guide trait-associated gene discovery for crop improvement.

The TaTCP4/10-B1 cascade regulates awn elongation in wheat(Triticum aestivum L.)

Awns are important morphological markers for wheat and exert a strong physiological effect on wheat yield.The awn elongation suppressor B1 has recently been cloned through association and linkage analysis in wheat.However,the mechanism of awn inhibition centered around B1 remains to be clarified.Here,we identified an allelic variant in the coding region of B1 through analysis of re-sequencing data;this variant causes an amino acid substitution and premature termination,resulting in a long-awn phenotype.Transcriptome analysis indicated that B1 inhibited awn elongation by impeding cytokinin-and auxinpromoted cell division.Moreover,B1 directly repressed the expression of TaRAE2 and TaLks2,whose orthologs have been reported to promote awn development in rice or barley.More importantly,we found that TaTCP4 and TaTCP10 synergistically inhibited the expression of B1,and a G-to-A mutation in the B1 promoter attenuated its inhibition by TaTCP4/10.Taken together,our results reveal novel mechanisms of awn development and provide genetic resources for trait improvement in wheat.

Paternally imprinted LATE-FLOWERING2 transcription factor contributes to paternal-excess interploidy hybridization barriers in wheat∞

Interploidy hybridization between hexaploid and tetraploid genotypes occurred repeatedly during genomic introgression events throughout wheat evolution,and is commonly employed in wheat breeding programs.Hexaploid wheat usually serves as maternal parent because the reciprocal cross generates progeny with severe defects and poor seed germination,but the underlying mechanism is poorly understood.Here,we performed detailed analysis of phenotypic variation in endosperm between two interploidy reciprocal crosses arising from tetraploid(Triticum durum,AABB)and hexaploid wheat(Triticum aestivum,AABBDD).In the paternal‐versus the maternal‐excess cross,the timing of endosperm cellularization was delayed and starch granule accumulation in the endosperm was repressed,causing reduced germination percentage.The expression profiles of genes involved in nutrient metabolism differed strongly between these endosperm types.Furthermore,expression patterns of parental alleles were dramatically disturbed in interploidy versus intraploidy crosses,leading to increased number of imprinted genes.The endosperm‐specific TaLFL2 showed a paternally imprinted expression pattern in interploidy crosses partially due to allele‐specific DNA methylation.Paternal TaLFL2 binds to and represses a nutrient accumulation regulator TaNAC019,leading to reduced storage protein and starch accumulation during endosperm development in paternal‐excess cross,as confirmed by interploidy crosses between tetraploid wild‐type and clustered regularly interspaced palindromic repeats(CRISPR)–CRISPR‐associated protein 9 generated hexaploid mutants.These findings reveal a contribution of genomic imprinting to paternal‐excess interploidy hybridization barriers during wheat evolution history and explains why experienced breeders preferentially exploit maternal‐excess interploidy crosses in wheat breeding programs.

A highly conserved amino acid in high molecular weight glutenin subunit 1Dy12 contributes to gluten functionality and processing quality in wheat

Bread wheat(Triticum aestivum L.)is one of the most commonly consumed staples worldwide,with widespread uses in foods such as breads,noodles,cakes,and cookies(Veraverbeke and Delcour,2002).The specific cooking properties of wheat products are mainly conferred by the gluten proteins contained in wheat grains(Delcour et al.,2012).High molecular weight glutenin subunits(HMW-GSs)are important constituents of wheat gluten proteins,largely determining gluten elasticity and processing quality(Branlard and Dardevet,1985;Payne et al.,1988).

TaANR1-TaMADS25 module regulates lignin biosynthesis and root development in wheat(Triticum aestivum L.)

Common wheat is a staple food for 35%of the global population,therefore increasing wheat yield in an ever-changing environment is essential for food security in the present day(Peng et al.,2011).Root system is responsible for water and nutrient acquisition,thus crucial for competitive fitness and crop yield in challenging environments(Karlova et al.,2021;Liu et al.,2022).Over the past decades,extensive research has focused on identifying genes accountable for root growth and development in plants(Rogers and Benfey,2015).However,only a limited number of genes have been cloned in wheat(Li et al.,2021).

Wheat genomic study for genetic improvement of traits in China

Bread wheat(Triticum aestivum L.)is a major crop that feeds 40%of the world’s population.Over the past several decades,advances in genomics have led to tremendous achievements in understanding the origin and domestication of wheat,and the genetic basis of agronomically important traits,which promote the breeding of elite varieties.In this review,we focus on progress that has been made in genomic research and genetic improvement of traits such as grain yield,end-use traits,flowering regulation,nutrient use efficiency,and biotic and abiotic stress responses,and various breeding strategies that contributed mainly by Chinese scientists.Functional genomic research in wheat is entering a new era with the availability of multiple reference wheat genome assemblies and the development of cutting-edge technologies such as precise genome editing tools,highthroughput phenotyping platforms,sequencing-based cloning strategies,high-efficiency genetic transformation systems,and speed-breeding facilities.These insights will further extend our understanding of the molecular mechanisms and regulatory networks underlying agronomic traits and facilitate the breeding process,ultimately contributing to more sustainable agriculture in China and throughout the world.

A natural variation in Ribonuclease H-like gene underlies Rht8 to confer“Green Revolution”trait in wheat

Dear Editor,Introduction of gibberellin(GA)-insensitive Reduced height(Rht)genes,Rht-B1b and Rht-D1b,has resulted in the“Green Revolution”in modern wheat cultivars(Triticum aestivum)that has skyrocketed wheat grain yields worldwide since the 1960s(Peng et al.,1999;Velde et al.,2021).However,Rht-B1b/D1b also reduce coleoptiles,which is undesired in dryland regions where deep planting is essential for seedling establishment(Rebetzke et al.,1999,Rebetzke et al.,2001;Ellis et al.,2004).

Ectopic expression of VRT-A2 underlies the origin of Triticum polonicum and Triticum petropavlovskyi with long outer glumes and grains

Polish wheat (Triticum polonicum) is a unique tetraploid wheat species characterized by an elongated outer glume. The genetic control of the long-glume trait by a single semi-dominant locus, P1 (from Polish wheat), was established more than 100 years ago, but the underlying causal gene and molecular nature remain elusive. Here, we report the isolation of VRT-A2, encoding an SVP-clade MADS-box transcription factor, as the P1 candidate gene. Genetic evidence suggests that in T. polonicum, a naturally occurring sequence rearrangement in the intron-1 region of VRT-A2 leads to ectopic expression of VRT-A2 in floral organs where the long-glume phenotype appears. Interestingly, we found that the intron-1 region is a key ON/OFF molecular switch for VRT-A2 expression, not only because it recruits transcriptional repressors, but also because it confers intron-mediated transcriptional enhancement. Genotypic analyses using wheat accessions indicated that the P1 locus is likely derived from a single natural mutation in tetraploid wheat, which was subsequently inherited by hexaploid T. petropavlovskyi. Taken together, our findings highlight the promoter-proximal intron variation as a molecular basis for phenotypic differentiation, and thus species formation in Triticum plants.

一个小麦强优势组合的杂种优势遗传基础解析

北方冬麦区骨干亲本农大3338与京冬6号组配的杂交F1代,在株高和千粒重等方面表现较强的中亲杂种优势.为解析该组合杂种优势形成的遗传基础,利用农大3338和京冬6号构建了双单倍体(doubled haploid,DH)群体,并利用DH群体衍生了一套包含283个杂交组合的小麦永久F_(2)群体,在两个不同环境下进行杂种优势评价.利用包含单核苷酸多态性(single nucleotide polymorphism,SNP)和简单重复序列(simple sequence repeat,SSR)分子标记的高密度整合遗传连锁图谱,基于完备区间作图法,对永久F_(2)群体在两个环境下的株高、千粒重、中亲优势值和相应的BLUP值进行全基因组数量性状基因座(quantitative trait locus,QTL)定位和上位性互作分析.共检测到32个株高QTL和25个千粒重QTL,分别解释0.54%~36.05%和0.87%~25.78%的表型变异,包含加性效应、显性效应和超显性效应位点,其中2D、4B、4D和6A染色体上存在稳定主效QTL,主要以加性效应为主.利用中亲优势值分别检测到13个株高杂种优势QTL和15个千粒重杂种优势QTL,绝大部分QTL表现为超显性效应.株高和千粒重上位性互作分析结果表明,在加加互作、加显互作、显加互作和显显互作4种不同互作类型中,显显互作的效应值最大,且所占比例最高.因此,本研究结果表明,超显性、显性和上位性是该组合杂种优势遗传基础的重要组成部分,为3种遗传效应共同调控杂种优势形成提供了有力的证据,对杂交小麦亲本创制和强优势组合选配具有重要意义.

The genetic and molecular basis for improving heat stress tolerance in wheat

Wheat production requires at least-2.4%increase per year rate by 2050 globally to meet food demands.However,heat stress results in serious yield loss of wheat worldwide.Correspondingly,wheat has evolved genetic basis and molecular mechanisms to protect themselves from heat-induced damage.Thus,it is very urgent to understand the underlying genetic basis and molecular mechanisms responsive to elevated temperatures to provide important strategies for heat-tolerant varieties breeding.In this review,we focused on the impact of heat stress on morphology variation at adult stage in wheat breeding programs.We also summarize the recent studies of genetic and molecular factors regulating heat tolerance,including identification of heat stress tolerance related QTLs/genes,and the regulation pathway in response to heat stress.In addition,we discuss the potential ways to improve heat tolerance by developing new technologies such as genome editing.This review of wheat responses to heat stress may shed light on the understanding heat-responsive mechanisms,although the regu-latory network of heat tolerance is still ambiguous in wheat.