TaCRT3 Is a Positive Regulator of Resistance to Blumeria graminis f. sp. tritici in Wheat.

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most prevalent diseases of wheat worldwide and can lead to severe yield reductions. Identifying genes involved in powdery mildew resistance will be useful for disease resistance breeding and control. Calreticulin (CRT) is a member of multigene family widely found in higher plants and is associated with a variety of plant physiological functions and defense responses. However, the role of CRT in wheat resistance to powdery mildew remains unclear. TaCRT3 was identified from the proteomic sequence of an incompatible interaction between the wheat (Triticum aestivum) cultivar Xingmin 318 and the Bgt isolate E09. Following analysis of transient expression of the GFP-TaCRT3 fusion protein in Nicotiana benthamiana leaves, TaCRT3 was localized in the nucleus, cytoplasm, and cell membrane. Transcript expression levels of TaCRT3 were significantly upregulated in the wheat-Bgt incompatible interaction. More critically, knockdown of TaCRT3 using virus-induced gene silencing resulted in attenuated resistance to Bgt in wheat. Histological analysis showed a significant increase in Bgt development in TaCRT3-silenced plants, whereas the pathogen-related gene was significantly downregulated in TaCRT3-silenced leaves. In addition, overexpression of TaCRT3 in wheat enhanced the resistance to powdery mildew, the growth of Bgt was significantly inhibited, and the area of H2O2 near the infection site and the expression of defense-related genes of the salicylic acid pathway significantly increased. These findings imply that TaCRT3 may act as a disease resistance factor that positively regulates resistance to powdery mildew, during which SA signaling is probably activated.

Effector Protein Serine Carboxypeptidase FgSCP Is Essential for Full Virulence in F. graminearum and Is Involved in Modulating Plant Immune Responses.

Fusarium head blight (FHB) caused by Fusarium graminearum is a significant pathogen affecting wheat crops. During the infection process, effector proteins are secreted to modulate plant immunity and promote infection. The toxin deoxynivalenol (DON) is produced in infected wheat grains, posing a threat to human and animal health. Serine carboxypeptidases (SCPs) belong to the α/ß hydrolase family of proteases and are widely distributed in plant and fungal vacuoles as well as animal lysosomes. Research on SCPs mainly focuses on the isolation, purification of a small number of fungi as well as their study in plants.However, their functions in F. graminearum, a fungal pathogen, remain relatively unknown. In this study, the biological functions of the FgSCP gene in F. graminearum were investigated. The study revealed that mutations in FgSCP affected nutritional growth, sexual reproduction, and stress tolerance of F. graminearum. Furthermore, the deletion of FgSCP resulted in reduced pathogenicity and hindered the biosynthesis of DON. The upregulation of FgSCP expression three days after infection indicated its involvement in host invasion, possibly acting as a "smokescreen" to deceive the host and suppress the expression of host defensive genes. Subsequently, we confirmed the secretion ability of FgSCP and its ability to inhibit the cell death induced by INF1 in Nicotiana. benthamiana cells, indicating its potential role as an effector protein in suppressing plant immune responses and promoting infection. In summary, we have identified FgSCP as an essential effector protein in F. graminearum, playing critical roles in growth, virulence, secondary metabolism, and host invasion.

QTL Mapping of Adult Plant Resistance to Powdery Mildew in Chinese Wheat Landrace Baidatou.

Wheat powdery mildew, caused by the biotrophic fungus Blumeria graminis f. sp. tritici (Bgt), is one of the most devastating diseases affecting wheat throughout the world. Breeding and growing resistant wheat cultivars is one of the most economic and effective methods to control the disease, and as such, identifying and mapping the new and effective resistance genes is critical. Baidatou, a Chinese wheat landrace, shows excellent field resistance to powdery mildew. To identify the resistance gene(s) in Baidatou, 170 F7:8 recombinant inbred lines (RILs) derived from the cross Mingxian 169/Baidatou were evaluated for powdery mildew response at the adult-plant stage in the experimental fields in Yangling (YL) of Shaanxi Province and Tianshui (TS) in Gansu Province in 2019, 2020, and 2021. The relative area under disease progress curve (rAUDPC) of Mingxian 169/Baidatou F7:8 RILs indicated that the resistance of Baidatou to powdery mildew was controlled by quantitative trait loci (QTLs). Based on bulk segregation analysis combined with the 660K single nucleotide polymorphism (SNP) array and genotyping by target sequencing (16K SNP) of the entire RIL population, two QTLs, QPmbdt.nwafu-2AS and QPmbdt.nwafu-3AS, were identified, and these accounted for up to 44.5% of the phenotypic variation. One of the QTLs was located on the 3.32 cM genetic interval on wheat chromosome 2AS between the kompetitive allele-specific PCR markers AX-111012288 and AX_174233809, and another was located on the 9.6 cM genetic interval on chromosome 3AS between the SNP markers 3A_684044820 and 3A_686681822. These markers could be useful for successful breeding of powdery mildew resistance in wheat.

Favorable Loci Identified for Stripe Rust Resistance in Chinese Winter Wheat Accessions via Genome-Wide Association Study.

Stripe rust (or yellow rust), caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases of wheat worldwide. Currently, the utilization of resistant cultivars is the most viable way to reduce yield losses. In this study, a panel of 188 wheat accessions from China was evaluated for stripe rust resistance, and genome-wide association studies were performed using high-quality Diversity Arrays Technology markers. According to the phenotype and genotype data, a total of 26 significant marker-trait associations were identified, representing 18 quantitative trait loci (QTLs) on chromosomes 1B, 2A, 2B, 3A, 3B, 5A, 5B, 6B, 7B, and 7D. Of the 18 QTLs, almost all were associated with adult plant resistance (APR) except QYr.nwsuaf-6B.2, which was associated with all-stage resistance (also known as seedling resistance). Three of the 18 QTLs were mapped far from previously identified Pst resistance genes and QTLs and were considered potentially new loci. The other 15 QTLs were mapped close to known resistance genes and QTLs. Subsequent haplotype analysis for QYr.nwsuaf-2A and QYr.nwsuaf-7B.3 revealed the degrees of resistance of the panel in the APR stage. In summary, the favorable alleles identified in this study may be useful in breeding for disease resistance to stripe rust.

Genetic Analysis Reveals Relationships Among Populations of Puccinia striiformis f. sp. tritici from Shaanxi-Gansu-Ningxia-Xinjiang of Northwestern and Sichuan-Yunnan of Southwestern China.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most destructive diseases worldwide. In China, wheat stripe rust generally occurs in the northwestern and southwestern regions; however, the genetic relationships of Pst populations between these regions are largely unclear. To determine the population structure and potential migration route in these regions, 235 isolates collected from Xinjiang (XJ), Gansu (GS), Ningxia (NX), Shaanxi (SX), Sichuan (SC), and Yunnan (YN) provinces in 2021 and 2022 were phenotyped using two sets of Pst differentials and genotyped using 20 competitive allele-specific PCR-single nucleotide polymorphism (KASP-SNP) markers. The phenotype tests indicated that CYR34, CYR32, and CYR33 were the predominant races with different occurrence frequencies in different regions and years. Genotypic analysis revealed that a total of 183 multilocus genotypes were identified, and the genetic diversity in the YN subpopulation was the highest. The genetic background in the SX subpopulation was similar to that in the GS and NX subpopulations, and the genetic background in the YN subpopulation was similar to that in the SC and SX subpopulations. A high level of gene flow (Nm) was found between the SX and GS, SX and NX, GS and NX, and SC and YN subpopulations, suggesting the migration of Pst among these regions, while a small amount of Nm existed between the SX and SC subpopulations. SC may serve as a bridge connecting Pst subpopulations between the northwestern provinces (SX, GS, and NX) and the southwestern provinces (SC and YN). With a relatively high genetic distance and low Nm values compared with other Pst subpopulations, XJ is considered a relatively independent epidemiological region in China. These results improved our current understanding of the wheat stripe rust epidemic in northwestern and southwestern regions of China.

Genome-wide identification, phylogenetic and expression pattern analysis of HSF family genes in the Rye (Secale cereale L.).

BACKGROUND: Heat shock factor (HSF), a typical class of transcription factors in plants, has played an essential role in plant growth and developmental stages, signal transduction, and response to biotic and abiotic stresses. The HSF genes families has been identified and characterized in many species through leveraging whole genome sequencing (WGS). However, the identification and systematic analysis of HSF family genes in Rye is limited. RESULTS: In this study, 31 HSF genes were identified in Rye, which were unevenly distributed on seven chromosomes. Based on the homology of A. thaliana, we analyzed the number of conserved domains and gene structures of ScHSF genes that were classified into seven subfamilies. To better understand the developmental mechanisms of ScHSF family during evolution, we selected one monocotyledon (Arabidopsis thaliana) and five (Triticum aestivum L., Hordeum vulgare L., Oryza sativa L., Zea mays L., and Aegilops tauschii Coss.) specific representative dicotyledons associated with Rye for comparative homology mapping. The results showed that fragment replication events modulated the expansion of the ScHSF genes family. In addition, interactions between ScHSF proteins and promoters containing hormone- and stress-responsive cis-acting elements suggest that the regulation of ScHSF expression was complex. A total of 15 representative genes were targeted from seven subfamilies to characterize their gene expression responses in different tissues, fruit developmental stages, three hormones, and six different abiotic stresses. CONCLUSIONS: This study demonstrated that ScHSF genes, especially ScHSF1 and ScHSF3, played a key role in Rye development and its response to various hormones and abiotic stresses. These results provided new insights into the evolution of HSF genes in Rye, which could help the success of molecular breeding in Rye.

Glutathione S-transferase interactions enhance wheat resistance to powdery mildew but not wheat stripe rust.

Wheat stripe rust and powdery mildew are important worldwide diseases of wheat (Triticum aestivum). The wheat cultivar Xingmin318 (XM318) is resistant to both wheat stripe rust and powdery mildew, which are caused by Puccinia striiformis f. sp. tritici (Pst) and Blumeria graminis f. sp. tritici (Bgt), respectively. To explore the difference between wheat defense response against Pst and Bgt, quantitative proteomic analyses of XM318 inoculated with either Pst or Bgt were performed using tandem mass tags technology. A total of 741 proteins were identified as differentially accumulated proteins (DAPs). Bioinformatics analyses indicated that some functional categories, including antioxidant activity and immune system process, exhibited obvious differences between Pst and Bgt infections. Intriguingly, only 42 DAPs responded to both Pst and Bgt infections. Twelve DAPs were randomly selected for reverse transcription quantitative polymerase chain reaction (RT-qPCR) analysis, and the mRNA expression levels of 11 were consistent with their protein expression. Furthermore, gene silencing using the virus-induced gene silencing system indicated that glutathione S-transferase (TaGSTU6) has an important role in resistance to Bgt but not to Pst. TaGSTU6 interacted with the cystathionine beta-synthase (CBS) domain-containing protein (TaCBSX3) in both Pst and Bgt infections. Knockdown of TaCBSX3 expression only reduced wheat resistance to Bgt infection. Overexpression of TaGSTU6 and TaCBSX3 in Arabidopsis (Arabidopsis thaliana) promoted plant resistance to Pseudomonas syringae pv. Tomato DC3000. Our results indicate that TaGSTU6 interaction with TaCBSX3 only confers wheat resistance to Bgt, suggesting that wheat has different response mechanisms to Pst and Bgt stress.

Wheat Class III Peroxidase TaPOD70 Is a Potential Susceptibility Factor Negatively Regulating Wheat Resistance to Blumeria graminis f. sp. tritici.

Powdery mildew, caused by Blumeria graminis f. sp. tritici (Bgt), is one of the most important diseases on wheat worldwide and can lead to a large reduction in wheat production. Class III peroxidases (PODs), a kind of secretory enzyme and members of a multigene family in higher plants, have been linked to various plant physiological functions and defensive responses. However, the role of PODs in wheat resistance to Bgt remains unclear. TaPOD70, a class III POD gene, was identified from the proteomics sequencing of the incompatible interaction between wheat (Triticum aestivum) cultivar Xingmin 318 and Bgt isolate E09. After transient expression of the TaPOD70-GFP fusion protein in Nicotiana benthamiana leaves, TaPOD70 was located in the membrane region. Yeast secretion assay showed that TaPOD70 was a secretory protein. Furthermore, Bax-induced programmed cell death was inhibited by transient expression of TaPOD70 in N. benthamiana. The transcript expression level of TaPOD70 was significantly upregulated in the wheat-Bgt compatible interaction. More crucially, knocking down TaPOD70 using virus-induced gene silencing increased wheat resistance to Bgt compared with the control plants. In response to Bgt, histological analyses indicated that hyphal development of Bgt was significantly reduced, whereas H2O2 production was enhanced in TaPOD70-silenced leaves. These findings imply that TaPOD70 may act as a susceptibility factor, adversely regulating wheat resistance to Bgt.

Identification and Molecular Mapping of the Gene YrFL in Wheat Cultivar Flanders with Durable Resistance to Stripe Rust.

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most severe diseases of wheat (Triticum aestivum L.) worldwide. Identification and characterization of resistance genes is advantageous to cultivating wheat varieties with durable resistance, which is the most economic and effective strategy to control stripe rust. Flanders, a common wheat cultivar released in France in 1986, confers effective resistance to stripe rust both at the seedling and adult plant stages. To elucidate the genetic basis of resistance in Flanders, F1, F2, and F2:3 generations derived from the cross Mingxian169 × Flanders were evaluated with the most prevalent Chinese Pst race CYR33 at the seedling stage. Inheritance analysis showed that the stripe rust resistance of Flanders was controlled by a single dominant gene, temporarily designated as YrFL. Bulked segregant analysis (BSA) combined with a wheat 660K single-nucleotide polymorphism (SNP) array indicated that polymorphic SNP markers were mainly located in the 0 to 150 Mb on wheat chromosome 5A. One hundred and eleven kompetitive allele-specific PCR (KASP) and 39 simple sequence repeat (SSR) markers on chromosome 5A were used to locate the YrFL. Linkage analysis mapped YrFL with 19 KASP and three SSR markers on wheat chromosome 5AS, and the genetic distances of the closest flanking markers AX108925494 and Xbarc56 to YrFL were 0.6 and 2.0 cM, respectively. Chromosome location, resistance characterization, and molecular marker positions indicated that YrFL is likely a novel stripe rust resistance gene on wheat chromosome 5AS and could be pyramided with other resistance genes to improve resistance in wheat breeding programs.

Resistance to Powdery Mildew Is Conferred by Different Genetic Loci at the Adult-Plant and Seedling Stages in Winter Wheat Line Tianmin 668.

Winter wheat line Tianmin 668 was crossed with susceptible cultivar Jingshuang 16 to develop 216 recombinant inbred lines (RILs) for dissecting its adult-plant resistance (APR) and all-stage resistance (ASR) against powdery mildew. The RIL population was genotyped on a 16K genotyping by target sequencing single-nucleotide polymorphism array and phenotyped in six field trials and in the greenhouse. Three loci-QPmtj.caas-2BL, QPmtj.caas-2AS, and QPmtj.caas-5AL-conferring APR to powdery mildew were detected on chromosomes 2BL, 2AS, and 5AL, respectively, of Tianmin 668. The effect of resistance to powdery mildew for QPmtj.caas-2BL was greater than that of the other two loci. A Kompetitive allele-specific PCR marker specific for QPmtj.caas-2BL was developed and verified on 402 wheat cultivars or breeding lines. Results of virulence and avirulence patterns to 17 Blumeria graminis f. sp. tritici isolates, bulked segregant analysis-RNA-sequencing, and a genetic linkage mapping identified a resistance allele at locus Pm4 in Tianmin 668 based on the seedling phenotypes of the RIL population. The PCR-based DNA sequence alignment and cosegregation of the functional marker with the phenotypes of the RIL population demonstrated that Pm4d was responsible for the ASR to isolate Bgt1 in Tianmin 668. The dissection of genetic loci for APR and ASR may facilitate the application of Tianmin 668 in developing powdery mildew-resistant wheat cultivars.

Genome-wide identification and expression analysis of the SPL transcription factor family and its response to abiotic stress in Quinoa (Chenopodium quinoa).

BACKGROUND: Squamous promoter binding protein-like (SPL) proteins are a class of transcription factors that play essential roles in plant growth and development, signal transduction, and responses to biotic and abiotic stresses. The rapid development of whole genome sequencing has enabled the identification and characterization of SPL gene families in many plant species, but to date this has not been performed in quinoa (Chenopodium quinoa). RESULTS: This study identified 23 SPL genes in quinoa, which were unevenly distributed on 18 quinoa chromosomes. Quinoa SPL genes were then classified into eight subfamilies based on homology to Arabidopsis thaliana SPL genes. We selected three dicotyledonous and monocotyledonous representative species, each associated with C. quinoa, for comparative sympatric mapping to better understand the evolution of the developmental mechanisms of the CqSPL family. Furthermore, we also used 15 representative genes from eight subfamilies to characterize CqSPLs gene expression in different tissues and at different fruit developmental stages under six different abiotic stress conditions. CONCLUSIONS: This study, the first to identify and characterize SPL genes in quinoa, reported that CqSPL genes, especially CqSPL1, play a critical role in quinoa development and in its response to various abiotic stresses.

Molecular cytogenetics and development of St-chromosome-specific molecular markers of novel stripe rust resistant wheat-Thinopyrum intermedium and wheat-Thinopyrum ponticum substitution lines.

BACKGROUND: Owing to their excellent resistance to abiotic and biotic stress, Thinopyrum intermedium (2n = 6x = 42, JJJsJsStSt) and Th. ponticum (2n = 10x = 70) are both widely utilized in wheat germplasm innovation programs. Disomic substitution lines (DSLs) carrying one pair of alien chromosomes are valuable bridge materials for transmission of novel genes, fluorescence in situ hybridization (FISH) karyotype construction and specific molecular marker development. RESULTS: Six wheat-Thinopyrum DSLs derived from crosses between Abbondanza nullisomic lines (2n = 40) and two octoploid Trititrigia lines (2n = 8x = 56), were characterized by sequential FISH-genome in situ hybridization (GISH), multicolor GISH (mc-GISH), and an analysis of the wheat 15 K SNP array combined with molecular marker selection. ES-9 (DS2St (2A)) and ES-10 (DS3St (3D)) are wheat-Th. ponticum DSLs, while ES-23 (DS2St (2A)), ES-24 (DS3St (3D)), ES-25(DS2St (2B)), and ES-26 (DS2St (2D)) are wheat-Th. intermedium DSLs. ES-9, ES-23, ES-25 and ES-26 conferred high thousand-kernel weight and stripe rust resistance at adult stages, while ES-10 and ES-24 were highly resistant to stripe rust at all stages. Furthermore, cytological analysis showed that the alien chromosomes belonging to the same homoeologous group (2 or 3) derived from different donors carried the same FISH karyotype and could form a bivalent. Based on specific-locus amplified fragment sequencing (SLAF-seq), two 2St-chromosome-specific markers (PTH-005 and PTH-013) and two 3St-chromosome-specific markers (PTH-113 and PTH-135) were developed. CONCLUSIONS: The six wheat-Thinopyrum DSLs conferring stripe rust resistance can be used as bridging parents for transmission of valuable resistance genes. The utility of PTH-113 and PTH-135 in a BC1F2 population showed that the newly developed markers could be useful tools for efficient identification of St chromosomes in a common wheat background.

Genetic Analysis Reveals Relationships Among Populations of Puccinia striiformis f. sp. tritici from the Longnan, Longdong, and Central Shaanxi Regions of China.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici, is one of the most important diseases of wheat worldwide. In China, Longnan (LN) and Longdong (LD) in the south and east of Gansu province, respectively, are important P. striiformis f. sp. tritici oversummering areas and are a source of P. striiformis f. sp. tritici inoculum for the major wheat-growing regions in eastern China. Central Shaanxi (CS) is a wheat-growing region that acts as an important bridge zone for stripe rust epidemic development between LN and LD in the west and the Huanghuai wheat-growing region in the east, and thus, it plays an essential role in P. striiformis f. sp. tritici epidemics in China. To study the relationships among P. striiformis f. sp. tritici populations in the three regions (LN, LD, and CS), we sampled 284 isolates from different geographic locations. Based on 10 simple sequence repeat markers, the results demonstrated high genetic diversity in all three regions, although diversity did vary among regions, with LN > LD > CS. Genetic differentiation was lower, with more extensive gene flow between LD and CS. P. striiformis f. sp. tritici populations in the CS region were genetically closer to those from LD than those from LN, which may be a result of geographical proximity and topography. A positive and significant correlation existed between linearized fixation index (FST) and the log of geographical distances among all subpopulations. Linkage disequilibrium analysis showed that subpopulations of P. striiformis f. sp. tritici from Qinzhou, Qincheng, Beidao, and Maiji from LN and Qianyang and Longxian from CS were in equilibrium (P > 0.05), suggesting that somatic hybridization and/or sexual reproduction may exist in these subpopulations.

Molecular Mapping of a Recessive Gene for Stripe Rust Resistance at the YrCf75 Locus Using Bulked Segregant Analysis Combined with Single Nucleotide Polymorphism Genotyping Arrays and Bulked Segregant RNA-Sequencing.

Wheat stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most important diseases in wheat worldwide. Planting resistant varieties is the most economical, effective, and environment-friendly measure to control wheat stripe rust. Changfeng 75, a Chinese winter wheat variety, shows high stripe rust resistance in both seedling and adult-plant stages. The seedling tests of F1, F2, and F2:3 populations derived from Mingxian 169/Changfeng 75 inoculated with Chinese predominant Pst race CYR34 showed that the stripe rust resistance of Changfeng 75 was controlled by a single recessive gene. The locus was temporarily designated as YrCf75. Bulked segregant analysis (BSA) combined with the wheat 660K single-nucleotide polymorphism (SNP) array and bulked segregant RNA-sequencing indicated that the proportion of polymorphic SNPs on wheat chromosome 2A was the highest, which suggested that YrCf75 was likely located on chromosome 2A. Two hundred and twenty-five Kompetitive allele-specific PCR (KASP) and 75 simple sequence repeat (SSR) markers on chromosome 2A were used to map YrCf75 using the BSA approach. Linkage analysis indicated that 31 KASP markers and one SSR marker were linked to YrCf75, and the genetic distances of the two closest flanking KASP markers, AX-1110060462 and AX-111004763, were 1.2 and 2.7 cM, respectively. YrCf75 was located on wheat chromosome 2AL. The molecular detection, resistance specificity, and chromosome location showed that YrCf75 is likely a new gene that is different from the known stripe rust resistance genes (Yr1 and Yr32) on wheat chromosome 2AL.

Genome-Wide Association Mapping of Resistance to Powdery Mildew in Regional Trials of Wheat Mainly from China.

Wheat powdery mildew (Blumeria graminis f. sp. tritici [Bgt]) is a widespread disease that causes significant economic losses to common wheat (Triticum aestivum L.) crops worldwide. To identify effective resistance genes, we evaluated 120 common wheat accessions mainly from different wheat producing regions in China for responses to different Bgt isolates in the seedling stage and to natural infection in three field trials and genotyped them with a wheat 55K iSelect single-nucleotide polymorphism array for a genome-wide association study. A total of 26 loci were identified, which explained 6.6 to 26.2% of the phenotypic variation depending on individual locus. Of the 26 loci, 10 were detected in the A genomes, 10 in the B genomes, and only 6 in the D genome. Sixteen loci overlapped with known powdery mildew resistance genes or quantitative trait loci, and the remaining 10 loci were potentially novel. This study improves the understanding of the genetic structure of wheat powdery mildew resistance and provides germplasms and information on genes and markers for breeding new wheat cultivars with effective resistance to powdery mildew.

Rapid Identification of a Stripe Rust Resistance Gene YrXK in Chinese Wheat Line Xike01015 Using Specific Locus Amplified Fragment (SLAF) Sequencing.

Wheat stripe rust, an airborne fungal disease caused by Puccinia striiformis Westend. f. sp. tritici, is one of the most devastating diseases of wheat. Chinese wheat cultivar Xike01015 displays high levels of all-stage resistance (ASR) to the current predominant P. striiformis f. sp. tritici race CYR33. In this study, a single dominant gene, designated YrXk, was identified in Xike01015 conferring resistance to CYR33 with genetic analysis of F2 and BC1 populations from a cross of Mingxian169 (susceptible) and Xike01015. The specific length amplified fragment sequencing (SLAF-seq) strategy was used to construct a linkage map in the F2 population. Quantitative trait loci (QTL) analysis mapped YrXk to a 12.4-Mb segment on chromosome1 BS, explaining >86.96% of the phenotypic variance. Gene annotation in the QTL region identified three differential expressed candidate genes, TraesCS1B02G168600.1, TraesCS1B02G170200.1, and TraesCS1B02G172400.1. The qRT-PCR results showed that TraesCS1B02G172400.1 and TraesCS1B02G168600.1 are upregulated and that TraesCS1B02G170200.1 is slightly downregulated after inoculation with CYR33 in the seedling stage, which indicates that these genes may function in wheat resistance to stripe rust. The results of this study can be used in wheat breeding for improving resistance to stripe rust.

Molecular Mapping of a Recessive Powdery Mildew Resistance Gene in Wheat Cultivar Tian Xuan 45 Using Bulked Segregant Analysis with Polymorphic Single Nucleotide Polymorphism Relative Ratio Distribution.

Powdery mildew is a destructive foliar disease of wheat worldwide. Wheat cultivar Tian Xuan 45 exhibits resistance to the highly virulent isolate HY5. Genetic analysis of the F2 and F2:3 populations of a cultivar Ming Xian 169/Tian Xuan 45 cross revealed that the resistance to HY5 was controlled by a single recessive gene, temporarily designated as PmTx45. A Manhattan plot with the relative frequency distribution of single nucleotide polymorphisms (SNPs) was used to rapidly narrow down the possible chromosomal regions of the associated genes. This microarray-based bulked segregant analysis (BSA) largely improved traditional analytical methods. PmTx45 was located in chromosomal bin 4BL5-0.86-1.00 and was flanked by SNP marker AX-110673642 and intron length polymorphism (ILP) marker ILP-4B01G269900 with genetic distances of 3.0 and 2.6 cM, respectively. Molecular detection in a panel of wheat cultivars using the markers linked to PmTx45 showed that the presence of PmTx45 in commercial wheat cultivars was rare. Resistance spectrum and chromosomal position analyses indicated that PmTx45 may be a novel recessive gene with moderate powdery mildew resistance. This new microarray-based BSA method is feasible and effective and has the potential application for mapping genes in wheat in marker-assisted breeding.

Genetic and Physical Mapping of a Putative Leymus mollis-Derived Stripe Rust Resistance Gene on Wheat Chromosome 4A.

Wheat stripe rust is one of the most damaging diseases of wheat worldwide. The wheat-Leymus mollis introgression line M8664-3 exhibits all-stage resistance to Chinese stripe rust races. Genetic analysis of stripe rust resistance was performed by crossing M8664-3 with the susceptible line Mingxian169. Analysis of the disease resistance of F2 and F2:3 populations revealed that its resistance to Chinese stripe rust race 33 (CYR33) is controlled by a single dominant gene, temporarily designated as YrM8664-3. Genetic and physical mapping showed that YrM8664-3 is located in bin 4AL13-0.59-0.66 close to 4AL12-0.43-0.59 on chromosome 4AL and is flanked by single-nucleotide polymorphism markers AX111655681 and AX109496237 with genetic distances of 5.3 and 2.3 centimorgans, respectively. Resistance spectrum and position analyses indicated that YrM8664-3 may be a novel gene. Molecular detection using the markers linked to YrM8664-3 with wheat varieties commonly cultivated and wheat-L. mollis-derived lines showed that YrM8664-3 is also present in other wheat-L. mollis introgression lines but absent in commercial common wheat cultivars. Thus, YrM8664-3 is a potentially valuable source of stripe rust resistance for breeding.

Application of Geographic Information Systems to Identify the Oversummering Regions of Blumeria graminis f. sp. tritici in China.

Blumeria graminis f. sp. tritici, the pathogen that causes wheat powdery mildew, can oversummer as mycelia or conidia on leaves of volunteer wheat plants in cool mountainous areas in China. In this study, the regions in China where B. graminis f. sp. tritici can oversummer were identified on the basis of the probability that temperature remains below a critical temperature that is lethal to B. graminis f. sp. tritici. Two methods, one describing the relationship between the average temperature (20 to 26°C) in a given continuous 10-day period and wheat powdery mildew severity, the other describing the relationship between the average temperature (26 to 33°C) and the number of lethal days on powdery mildew development, were used to calculate the oversummering probability using weather data for 743 sites across China. Spatial interpolation based on the ordinary kriging method was conducted for the regions without observation. Oversummering probability values were similar for most locations estimated between the two methods. The B. graminis f. sp. tritici oversummering regions in China were identified to be in mountainous or high-elevation areas, including most regions of Yunnan, west and central areas of Guizhou, south and northwest Sichuan, south and east Gansu, south Ningxia, north and west Shaanxi, central-north Shanxi, west Henan and Hubei, and some regions in Qinghai, Tibet, and Xinjiang. When the oversummering sites from this study were compared with observed survey data for some of these sites, about 90% of sites where B. graminis f. sp. tritici oversummering was observed had been found suitable by both methods. The coincidence frequency and the area under the receiver operating characteristic curve for model 2 were higher, albeit only slightly, than those for model 1. Thus, both methods may be used to assist in disease management and further investigation on pathogen oversummering.

Protein Disulfide Isomerase FgEps1 Is a Secreted Virulence Factor in Fusarium graminearum.

Protein disulfide isomerase (PDI) is a member of the thioredoxin (Trx) superfamily with important functions in cellular stability, ion uptake, and cellular differentiation. While PDI has been extensively studied in humans and animals, its role in fungi remains relatively unknown. In this study, the biological functions of FgEps1, a disulfide bond isomerase in the fungal pathogen Fusarium graminearum, were investigated. It was found that FgEps1 mutation affected nutritional growth, asexual and sexual reproduction, and stress tolerance. Additionally, its deletion resulted in reduced pathogenicity and impaired DON toxin biosynthesis. The involvement of FgEps1 in host infection was also confirmed, as its expression was detected during the infection period. Further investigation using a yeast signal peptide secretion system and transient expression in Nicotiana benthamiana showed that FgEps1 suppressed the immune response of plants and promoted infection. These findings suggest that virulence factor FgEps1 plays a crucial role in growth, development, virulence, secondary metabolism, and host infection in F. graminearum.