Susceptible Wheat Varieties Research Articles

The role of jasmonic acid signalling in wheat (Triticum aestivum L.) powdery mildew resistance reaction

Jasmonic acid (JA) signalling plays an important role in plant resistance to pathogens. Previously, JA has been found to play a role in induced disease resistance to necrotrophic pathogens in various plant species, but current researches showed that JA also enhanced resistance to biotrophic pathogens. However, its role in wheat (Triticum aestivum L.) powdery mildew (Blumeria graminis f. sp. tritici, Bgt) resistance reaction is largely unknown. To settle this issue, several typical powdery mildew resistant and susceptible wheat varieties were employed. The sensitivity to exogenous methyl jasmonate (MeJA) to wheat powdery mildew resistance, the concentration fluctuation of endogenous JAs after Bgt inoculation, and the expression profiles of nine pathogenesis-related protein genes (PR genes) after MeJA and Bgt treatments were studied systematically. Exogenous MeJA significantly enhanced the powdery mildew resistance of the susceptible varieties. After inoculation with Bgt, endogenous JAs accumulated rapidly, reached the maxima at 2 to 5 h post-inoculation (hpi), then decreased rapidly, and the concentration was almost the same as that of un-inoculated control at 96 hpi. The expression levels of the nine PRs were measured by real time quantitative RT-PCR (qRT-PCR) at different time points after MeJA application or Bgt inoculation respectively. The MeJA and Bgt strongly activated PR1, PR2, PR3, PR4, PR5, PR9, PR10 and Ta-JA2, but almost didn’t affect Ta-GLP2a. The induced powdery mildew resistance was positively correlated with the activated PR genes. JA plays a positive role in defence against Bgt. JA is a signalling molecule in wheat powdery mildew resistance and future manipulation of this pathway may improve powdery mildew resistance in wheat breeding.

Fitness Attributes ofFusarium graminearumIsolates from Wheat in New York Possessing a 3-ADON or 15-ADON Trichothecene Genotype

In all, 50 isolates of Fusarium graminearum from wheat spikes in New York, including 25 isolates each of the 15-acetyl-deoxynivalenol (15-ADON) and 3-ADON genotype, were tested to determine whether 3-ADON isolates are more fit for saprophytic survival and pathogenicity on wheat spikes than are 15-ADON isolates. The isolates were characterized and compared for 14 different attributes of saprophytic fitness and pathogenic fitness on a susceptible wheat variety. Isolates of the two genotypes could not be differentiated for most of these traits. Three principle components-ascospore production on corn stalks, total trichothecene amount in wheat kernels, and incidence of diseased spikelets up from the point of inoculation-accounted for 29.4, 18.9, and 10.8% of the variation among the isolates, respectively. A bootstrapping procedure grouped the isolates into two distinct groups, with 27 and 23 isolates each, with isolates from both genotypes represented in similar proportions (15-ADON/3-ADON, n = 14/13 and 11/12). Within the contemporary population of F. graminearum causing wheat head blight in New York, isolates with a 3-ADON genotype did not possess any detectable advantage over isolates with a 15-ADON genotype in saprophytic fitness or in pathogenic fitness on a susceptible wheat cultivar.

Combining multiple rust resistance genes by phenotypic and marker assisted selection in wheat(Triticum aestivumL.)

Development of cultivars with genetic resistance has been the most effective and economical strategy to control rust diseases of wheat (Triticum aestivum L.). Leaf rust (Puccinia triticina) and stripe rust (Puccinia striiformis) are the two most important diseases of wheat in India. Combining two or more major rust resistance genes into one highly adapted cultivar is one of the important strategies for obtaining durable resistance. Molecular markers have made it possible to identify and pyramid valuable genes of agronomic importance in resistance breeding. The leaf rust resistance genes Lr24, Lr28 and stripe rust resistance gene Yr15 were pyramided into a popular but rust susceptible wheat variety HD2687 using marker assisted backcross breeding. SCAR markers SCS1302607 for Lr24 and SCS421570 for Lr28 and SSR marker Xgwm273 for Yr15 gene were used to select gene positive plants. Different combinations of the three resistance genes were selected in BC4F2 generation of HD2687 with the help of linked molecular markers. Agronomic performance of improved lines was compared with that of the recipient parent.

Spontaneous loss of Yr2 avirulence in two lineages of Puccinia striiformis did not affect pathogen fitness

Fitness costs associated with the emergence of virulence (loss of avirulence) have been a subject of much debate in plant pathology. Here, differences in fitness between two pairs of wild types and spontaneous virulence mutants in Puccinia striiformis were studied. The mutants differed from their respective wild types in virulence corresponding to the Yr2 resistance gene in wheat. The wildtype and mutant pairs represented different genetic lineages and virulence phenotypes. Colony size, latent period, lesion growth rate and uredinium density and size were assessed on susceptible and Yr2 resistant wheat varieties. No significant difference was observed for any of the evaluated parameters within wildtype and mutant pairs, i.e. the results did not support a hypothesis of a fitness cost for acquiring virulence in P. striiformis. In contrast, significant differences were found for most of the parameters when isolates were compared according to genetic lineage, which confirm that the applied methodologies were appropriate for detecting differences in pathogen fitness.

The comparison of leaf protein patterns between two tolerant and susceptible varieties of wheat under drought stress

The comparison of leaf protein patterns between two tolerant and susceptible varieties of wheat under drought stress

RLP1.1, a novel wheat receptor-like protein gene, is involved in the defence response against Puccinia striiformis f. sp. tritici

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most serious diseases of wheat; therefore, exploring effective resistance-related genes is critical for breeding and studying resistance mechanisms. However, only a few stripe rust resistance genes and defence-related genes have been cloned. Moreover, transgenic wheat with enhanced stripe rust resistance has rarely been reported. Receptor-like proteins (RLPs) are known to be involved in defence and developmental pathways. In this research, a novel RLP gene TaRLP1.1 was characterized as an important stripe rust defence gene. TaRLP1.1 was screened by GeneChip and was found to be induced by Pst specifically in the resistant variety. Knock down of TaRLP1.1 in the stripe rust-resistant plants resulted in increased susceptibility to Pst, and phenolic autofluorogen accumulation at the pathogen–host interaction sites, usually correlated with the hypersensitive response, was decreased dramatically. However, when the TaRLP1.1 gene was transformed into the susceptible wheat variety Yangmai158, the transgenic plants showed highly increased resistance to Pst, and the hypersensitive response was enhanced at the infection sites. Meanwhile, the expression of pathogenesis-related genes decreased in the TaRLP1.1-silenced plants and increased in the TaRLP1.1-overexpressing plants. Thus, it was proposed that TaRLP1.1 greatly contributed to the hypersensitive response during the pathogen–host interaction. Along with the functional analysis, an evolutionary study of the TaRLP1 family was performed. Characterization of TaRLP1.1 may facilitate breeding for stripe rust resistance and better understanding of the evolution of the RLP genes in wheat.

Seeding date and location affect winter wheat infection by common bunt (Tilletia tritici and T. laevis) in western Canada

Gaudet, D. A., Puchalski, B. J., Despins, T., McCartney, C., Menzies, J. G. and Graf, R. J. 2013. Seeding date and location affect winter wheat infection by common bunt (Tilletia tritici and T. laevis) in western Canada. Can. J. Plant Sci. 93: 483–489. The majority of western Canadian winter wheat varieties are susceptible to common bunt (Tilletia tritici and T. laevis) and the risk to production, particularly in Saskatchewan and Manitoba, where the majority of production occurs, is unknown. Inoculated trials were employed to determine the effects of fall seeding date on bunt infection levels on one resistant and two susceptible winter wheat varieties at three locations in western Canada during three growing seasons from 2007/2008 to 2009/2010. Among the three locations, average infection levels were highest in Lethbridge, AB, followed by Glenlea, MB, and Saskatoon, SK. Later seeding resulted in high infection levels at all three locations in the susceptible varieties, particularly in Lethbridge, but high infection levels were observed in the earliest seeded treatments at both the Saskatchewan and Manitoba locations. The resistant variety Blizzard consistently exhibited infection levels of less than 3% infection across all environments. In a second test at conducted at Lethbridge, 10 of the 11 currently grown winter wheat varieties were susceptible to common bunt. These results indicate that there is a general risk of common bunt infection to winter wheat production across western Canada and that control measures must be taken until resistant varieties are developed.

English

Wheat is an important staple food crop in sub-Saharan Africa. However, the current wheat consumption of 900 000 tons in Kenya outweighs the wheat production of 350 000 tons given the high population growth and inflation. The stem rust currently poses the greatest threat to wheat production due to the emergence of the virulent race of thePuccinia graminis f. sp tritici, Ug99 (TTKS) and its variants Ug99 + Sr24 (TTKSK) andUg99 + Sr36 (TTKST) leading to about 70 to 100% yield losses. This study aimed at evaluating twenty-five wheat genotypes for both field and seedling resistance to stem rust. The genotypes were grown in an alpha lattice design and in two replicates both in the greenhouse and in the field at Kenya Agricultural Research Institute (KARI), Njoro.  The seedling stage infection types were scored based on Stakman et al. (1962) scale. At the adult plant stages, the stem rust disease severity was based on modified Cobb’s scale. The genotypes showed diverse seedling and adult plant resistance responses. The most resistant entries, KSL-2, KSL-3 and KSL-20 also exhibited the pseudo black chaff (PBC) trait implying they contain the Sr2 gene in their background; the basis of breeding for durable resistance to stem rust in wheat. These lines with high stem rust resistance could be backcrossed to the adapted and high yielding but susceptible Kenyan wheat varieties to avert further wheat yield declines.   Key words: Stem rust, wheat, Ug99, resistance, disease severity.

Cloning of a Conserved Receptor-Like Protein Kinase Gene and Its Use as a Functional Marker for Homoeologous Group-2 Chromosomes of the Triticeae Species

Receptor-like kinases (RLKs) play broad biological roles in plants. We report on a conserved receptor-like protein kinase (RPK) gene from wheat and other Triticeae species. The TaRPK1 was isolated from the Triticum aestivum cv. Prins - Triticum timopheevii introgression line IGVI-465 carrying the powdery mildew resistance gene Pm6. The TaRPK1 was mapped to homoeologous chromosomes 2A (TaRPK1-2A), 2D (TaRPK1-2D) and the Pm6-carrier chromosome 2G (TaRPK1-2G) of IGVI-465. Under the tested conditions, only the TaRPK1-2G allele was actively transcribed, producing two distinct transcripts via alternative splicing. The predicted 424-amino acid protein of TaRPK1-2G contained a signal peptide, a transmembrane domain and an intracellular serine/threonine kinase domain, but lacked a typical extracellular domain. The expression of TaRPK1-2G gene was up-regulated upon the infection by Blumeria graminis f.sp. tritici (Bgt) and treatment with methyl jasmonate (MeJA), but down-regulated in response to treatments of SA and ABA. Over-expression of TaRPK1-2G in the powdery mildew susceptible wheat variety Prins by a transient expression assay showed that it slightly reduced the haustorium index of the infected Bgt. These data indicated that TaRPK1-2G participated in the defense response to Bgt infection and in the JA signaling pathway. Phylogenetic analysis indicated that TaRPK1-2G was highly conserved among plant species, and the amino acid sequence similarity of TaRPK1-2G among grass species was more than 86%. Based on its conservation, the RPK gene-based STS primers were designed, and used to amplify the RPK orthologs from the homoeologous group-2 chromosomes of all the tested Triticeae species, such as chromosome 2G of T. timopheevii, 2R of Secale cereale, 2H of Hordeum vulgare, 2S of Aegilops speltoides, 2Sl of Ae. longissima, 2Mg of Ae. geniculata, 2Sp and 2Up of Ae. peregrina. The developed STS markers serve as conserved functional markers for the identification of homoeologous group-2 chromosomes of the Triticeae species.

3-D imaging of temporal and spatial development of Puccinia striiformis haustoria in wheat

Differentiation of haustoria on primary infection hyphae of the fungal pathogen Puccinia striiformis was studied in wheat seedlings with two-photon microscopy in combination with a classical staining technique. Our results showed a significant increase in the average haustorium size 22, 44, 68, 92 and 116 h after inoculation (hai). After 116 hai no significant change was observed until 336 hai. Haustorium morphology also changed significantly during the time of infection. Initially small spherical haustoria were seen, but as they grew the haustoria gradually became apically branched. At 22 hai all observed haustoria were spherical, but at 44 hai most haustoria had an irregular structure, and at 92 hai all observed haustoria appeared branched. Along with the changes of the haustorial body the haustorial neck changed from narrow and slender to having an expanded appearance with a rough and invaginated structure. The structural changes were similar in two susceptible wheat varieties, 514W and Cartago, although the mean haustorium size was larger in 514W than in Cartago at all intervals.

Vp1 expression profiles during kernel development in six genotypes of wheat, triticale and rye

During the last few decades, the physiological and genetic background of dormancy, and correlated pre-harvest sprouting (PHS) have been intensively investigated. Special attention has often been paid to genetic factors that may explain and predict PHS susceptible behaviour. A major candidate is the Vp1 gene which is involved in embryo development and maturation as well as in dormancy establishment. In this study, Vp1 gene expression during kernel development was studied in wheat, triticale and rye as a potential biomarker for selecting PHS tolerant varieties in cereal breeding programs. Plants of known PHS tolerant and PHS susceptible varieties were grown under controlled conditions from flowering until harvest ripeness. During that period, kernels were regularly harvested for RNA extraction and cDNA synthesis. Calibrated and normalized relative Vp1 expression levels were obtained in an RT-qPCR assay. During kernel development, Vp1 expression levels generally showed a typical peak during the soft dough stage, after which they decreased and remained low until harvest maturity. Differences in Vp1 expression levels could be observed between the PHS susceptible and PHS tolerant varieties of wheat, with the PHS tolerant variety showing higher levels of relative Vp1 expression compared to the PHS susceptible variety. In triticale, however, this difference was only seen once and could not be confirmed in further experiments. It seems that the Vp1 gene in triticale behaves in a similar way as in rye, in which no specific trends could be observed.

Physiological parameters for evaluating drought tolerance in durum wheat varieties grown in the fields in Syria

Wheat is necessary to ensure a stable food style everywhere in the world. During the past few years wheat production in Syria fluctuated enormously, one important reason was climate change and more precisely drought. A physiological approach can complement empirical breeding and can enhance the rate of yield improvement under drought condition by identification important physiological traits associated with drought tolerance. This investigation was carried out under field conditions in the 1st and 2nd settlement zone in Syria (under water limited condition) with some drought tolerant and susceptible durum wheat varieties. Membrane stability index, relative water content, chlorophyll content and chlorophyll fluorescence were measured at vegetative, anthesis and post anthesis stage. Our findings showed that all varieties were superior in all physiological parameters under study as grown in the 1st settlement zone compared with the 2nd zone at all growth stages. More reduction in all physiological characters was recorded in drought susceptible variety in bohouth, which showed also more reduction in yield and yield components. Drought tolerant variety in douma were more stable and showed better adaptation and comparatively better physiological performance and higher yield under drought stress condition. This study lays emphasis on the importance of these traits particularly for breeder for improving drought stress tolerance.

Effect of Drought on Different Physiological Characters and Yield Component in Different Varieties of Syrian Durum Wheat

Tolerant and susceptible durum wheat varieties were grown in the 1st and 2nd settlement zone under rainfed conditions inDaraa province-Syria, In order to expose plants to different level of water regime, since the two zones differ in total amount of rainfall during the growing season. Plants were suffered from terminal drought stress in both zones, however, the drought was more sever in the 2nd settlement zone. All measured parameters: chlorophyll content, MSI, RWC, Fv/Fm decreased significantly in the 2nd compared to the 1st zone at all growth stages, however more reduction was recorded in drought susceptible varieties. Yield all yield components also affected negatively and drought tolerant varieties have maintained good performance in the 2nd zone. Our results proved that Chlorophyll content, MSI, RWC and Fv/Fm are good physiological indices of drought tolerance and can be used for improvement drought tolerance in wheat.

Enhancing Fusarium crown rot resistance of durum wheat by introgressing chromosome segments from hexaploid wheat

Compared with hexaploid wheat, tetraploid durum is more susceptible to Fusarium crown rot (FCR) infection. The feasibility of enhancing FCR resistance in durum wheat by introgressing chromosome segments of hexaploid wheat was investigated by generating and analysing a backcross population derived from a susceptible durum wheat variety ‘Bellaroi’ (recurrent parent) and a resistant hexaploid genotype ‘CSCR6’ (donor parent). Together with a few scattered segments on various chromosomes, segments of a large section of the donor chromosome 6B showed a significant effect in enhancing FCR resistance in the durum background. However, a known major locus on the donor 3BL conferring high level of resistance to FCR in hexaploid wheat failed to provide any improvement in resistance than that of the genome average once it was introduced into the durum wheat. A small proportion of the backcross population gave similar resistance to the bread wheat variety ‘Kennedy’, a level of FCR resistance acceptable to durum growers. These lines share a 4B segment from the hexaploid donor, although the segment was not among those with the largest individual effect across the whole population. These results show that it is feasible to improve FCR resistance of durum wheat by exploiting hexaploid chromosome segments, although resistance loci of the hexaploid wheat may not function properly in durum backgrounds.

Serine/threonine kinase gene Stpk-V , a key member of powdery mildew resistance gene Pm21 , confers powdery mildew resistance in wheat

Powdery mildew resistance gene Pm21, located on the chromosome 6V short arm of Haynaldia villosa and transferred to wheat as a 6VS·6AL translocation (T6VS·6AL), confers durable and broad-spectrum resistance to wheat powdery mildew. Pm21 has become a key gene resource for powdery mildew resistance breeding all over the world. In China, 12 wheat varieties containing Pm21 have been planted on more than 3.4 million hectares since 2002. Pm21 has been intractable to molecular genetic mapping because the 6VS does not pair and recombine with the 6AS. Moreover, all known accessions of H. villosa are immune to powdery mildew fungus. Pm21 is still defined by cytogenetics as a locus. In the present study, a putative serine and threonine protein kinase gene Stpk-V was cloned and characterized with an integrative strategy of molecular and cytogenetic techniques. Stpk-V is located on the Pm21 locus. The results of a single cell transient expression assay showed that Stpk-V could decrease the haustorium index dramatically. After the Stpk-V was transformed into a susceptible wheat variety Yangmai158, the characterized transgenic plants showed high and broad-spectrum powdery mildew resistance similar to T6VS·6AL. Silencing of the Stpk-V by virus-induced gene silencing in both T6VS·6AL and H. villosa resulted in their increased susceptibility. Stpk-V could be induced by Bgt and exogenous H(2)O(2), but it also mediated the increase of endogenous H(2)O(2), leading to cell death and plant resistance when the plant was attacked by Bgt.

The differential expression of Rhopalosiphum padi resistance in sibling wheat-rye amphiploids

Thirteen amphiploids were synthesized by chromosome doubling of an F1 plant of a cross between Triticum aestivum Mianyang11 × S. cereale Kustro, which shows resistance to Bird cherry-oat aphid (Rhopalosiphum padi). The amphiploids were confirmed by GISH analysis and tested for their reaction to R. padi. Eleven amphiploids exhibited resistance to R. padiand two of them exhibited high level of susceptibility. The PCR analysis using rye-specific markers provided evidence for the elimination of W-box elements from the susceptible amphiploids. The possible mechanism of loss resistance in some amphiploids was discussed. The resistant amphiploids can be exploited in wheat breeding programs to transfer R. padi resistance to susceptible wheat varieties. Key words: Rhopalosiphum padi, amphiploid, wheat, rye.

Molecular cloning of a new wheat calreticulin gene TaCRT1 and expression analysis in plant defense responses and abiotic stress resistance

Calreticulin proteins play essential roles in regulating various metabolic processes and in molecular signal transduction in animals and plants. Using homologous PCR, we screened a cDNA library of the wheat resistance gene Yr5 from a near-isogenic line in the susceptible common wheat variety Taichung 29, which was inoculated with an incompatible race CYR32 of Puccinia striiformis. We isolated a novel full-length cDNA encoding calreticulin protein, which we named TaCRT1. Sequence analyses indicated that TaCRT1 contains an open reading frame of 1287 bp in length; it was deduced to encode 428 amino acids. Clustering analysis showed that TaCRT1 belongs to group III of the calreticulin protein family. Semi-quantitative RT-PCR was used to analyze expression profiles of the isolated gene under biotic and abiotic stresses. Expression of TaCRT1 was suppressed by exogenous application of phytohormones, such as abscisic acid and methyl jasmonate, and by dehydration; but it was induced by CYR32 infection and cold treatment. Based on the expression patterns, we propose that TaCRT1 participates in regulatory processes involved in defense responses and stress resistance in wheat.

On-farm experiments over 5 years in a grain maize/winter wheat rotation: effect of maize residue treatments on Fusarium graminearum infection and deoxynivalenol contamination in wheat

Over the course of 5 years, different maize residue treatments were conducted on 14 zero tillage on-farm sites in Switzerland to evaluate their effect on the development of Fusarium head blight (FHB) and the contamination with the mycotoxin deoxynivalenol (DON) in winter wheat grains and wheat straw following grain maize. Two experimental series with three and five different treatments were carried out, respectively. Fusarium graminearum (Schwabe) was the predominant FHB-causing species with an overall incidence of 15% infected wheat grains. A significant correlation between symptoms in the field, F. graminearum incidence and DON content in wheat grains and wheat straw was observed. The average DON content in both wheat grains and wheat straw was approximately 5,000 μg/kg and thus several times higher than the European maximum limit of 1,250 μg/kg for unprocessed small-grain cereals for human consumption. Of all grain samples, 74% were above the maximum limit. Pooled over both experimental series, the average reduction of DON in grains through treatments of the maize residue compared with a control treatment ranged between 21 and 38%. The effect of various other factors, including the year, the wheat variety, the site, the maize hybrid and the production system was evaluated as well. The year and the wheat variety were the most important FHB influencing factors. Over all treatments, the variety Levis showed a fivefold higher average DON content compared with the variety Titlis. From different categories of maize residue particles, intact pieces of 5-15 cm length were strongly correlated with F. graminearum incidence and DON content in grains. During the time course of this study, the recommendation from a preliminary version of the internet-based DON forecasting system FusaProg to apply or to omit a fungicide treatment was correct in 32 out of 42 cases. The results are currently being used to optimise the FusaProg models. This study has shown that in a grain maize/winter wheat rotation, the DON content in wheat grains frequently exceeded the European maximum limit, even with a thorough treatment of maize residues and less susceptible wheat varieties. Hence, in order to reduce the contamination risk in a zero tillage system, the crop rotation needs to be modified.

Phylogenetic Relationship to Study the Ploidy Status and Resistance to Karnal Bunt in Indian Wheat Cultivars Using RAPD Technique

Tetraploid and hexaploid Indian wheat accessions were analyzed for genetic polymorphism using RAPD-PCR in order to study the gene rearrangements during polyploidization. Ten RAPD primers were employed to establish the evolutionary relationship amongst 10 tetraploid and 17 hexaploid wheat accessions. Tetraploid accession showed 75.7% polymorphism whereas hexaploid accessions showed 65.3% polymorphism. The Genetic Distance (GD) value of the tetraploid accessions ranged 0.400 to 0.966 was significantly higher than the GD values of the hexaploid accessions (0.630 to 0.952). RAPD primers clearly categorized tetraploid to hexaploid accessions in different groups according to similarity coefficient. Nearly all tetraploid accessions were grouped together. The same set of primers was also able enough to establish polymorphism amongst 20 Karnal bunt susceptible and resistant tetra and hexaploid wheat varieties. Like tetraploid accessions, susceptible varieties showed low genetic relationship. Some of the primers gave a distinct RAPD pattern for the discrimination between resistant and susceptible varieties but none of the primer was able to discriminate the resistant, susceptible and moderately susceptible wheat varieties. The phylogenetic polymorphism according to ploidy level and resistant status to KB is interpreted as the result of alteration in gene loci during polyploidization, genetic drift during inter and intra specific breeding andlor selection pressure for improved fertility.

Plastidial Glutathione Reductase from Haynaldia villosa is an Enhancer of Powdery Mildew Resistance in Wheat (Triticum aestivum)

A full-length cDNA (Hv-GR) whose transcript accumulation increased in response to infection by Blumeria graminis DC.f.sp. tritici (Bgt) was isolated from Haynaldia villosa. Southern analysis revealed a single copy of Hv-GR present in H. villosa. This gene encodes a glutathione reductase (GR) with high similarity to chloroplastic GRs from other plant species. Chloroplastic localization of Hv-GR was confirmed by targeting of the green fluorescent protein (GFP)-Hv-GR fusion protein to chloroplasts of epidermal guard cells. Following inoculation with Bgt, transcript accumulation of Hv-GR increased in a resistant line of wheat, but no significant change was observed in a susceptible line. In vivo function of Hv-GR in converting oxidized glutathione (GSSG) to the reduced form (GSH) was verified through heterologous expression of Hv-GR in a yeast GR-deficient mutant. As expected, overexpression of this gene resulted in increased resistance of the mutant to H(2)O(2), indicating a critical role for Hv-GR in protecting cells against oxidative stress. Moreover, overexpression of Hv-GR in a susceptible wheat variety, Triticum aestivum cv. Yangmai 158, enhanced resistance to powdery mildew and induced transcript accumulation of other pathogenesis-related genes, PR-1a and PR-5, through increasing the foliar GSH/GSSG ratio. Therefore, we concluded that a high ratio of GSH to GSSG is required for wheat defense against Bgt, and that chloroplastic GR enzymes might serve as a redox mediator for NPR1 activation.