Characterization of wheat monogenic lines with known Sr genes and wheat cultivars for resistance to three new races of Puccinia graminis f. sp. tritici in China

Wheat stem rust, caused by Puccinia graminis f. sp. tritici(Pgt), is a potentially devastating fungal disease of wheat worldwide. The present study was to evaluate the resistance of 42 wheat monogenic lines with known stem rust resistance(Sr) genes and 69 wheat cultivars to three new Pgt races(34C0MRGQM, 34C3MKGQM, and 34C6MTGSM)identified from aeciospores at the seedling and adult-plant stages. The phenotyping results revealed that monogenic lines harboring resistance genes Sr9e, Sr17, Sr21, Sr22, Sr26, Sr30, Sr31, Sr33, Sr35, Sr36, Sr37, Sr38, Sr47, SrTmp,and SrTt3 were effectively resistant to all three Pgt races at the seedling and adult-plant stages. In contrast, monogenic lines containing Sr5, Sr6, Sr7b, Sr9a, Sr9d, Sr9f, Sr9g, Sr9b, Sr16, Sr24, Sr28, and Sr39 were highly susceptible to these races at both seedling and adult-plant stages. The other lines with Sr8a, Sr10, Sr11, Sr13, Sr14, Sr15, Sr18, Sr20,Sr19, Sr23, Sr25, Sr27, Sr29, Sr32, and Sr34, displayed variable levels of resistance to one or two of the tested races.Seedling infection types(ITs) and adult-plant infection responses(IRs) indicated that 41(59.4%) of the wheat cultivars showed high resistance to all the three races. Molecular marker analysis showed that four wheat culitvars likely carried Sr2, 20 wheat culitvars likely carried Sr31, 9 wheat culitvars likely carried Sr38, and none of the cultivars carried Sr24,Sr25, and Sr26. Our results provide a scientific basis for rational utilization of the tested Sr genes and wheat cultivars against these novel Pgt races.

Yr5-virulent races of Puccinia striiformis f.sp.tritici possess relative parasitic fitness higher than current main predominant races and potential risk

Wheat stripe rust,caused by Puccinia striiformis f.sp.tritici(Pst),is one of the most destructive fungal diseases of wheat,and seriously threatens safe production of the crop worldwide.In China,new races historically appeared and rapidly developed to be predominant races and have resulted in ineffectiveness and replacement of wheat resistance cultivars as well as massive reduction in yield.In the present study,the relative parasitic fitness of the two newlyemerged Yr5-virulent races(TSA-6 and TSA-9)were compared with those of four currently predominant Chinese races(CYR31,CYR32,CYR33,and CYR34)based on evaluation on 10 Chinese wheat cultivars.As a result,there were significant differences in the relative parasitic fitness parameters among overall tested races based on multiple comparison(LSD)analysis(P<0.05).The principal component analysis(PCA)of overall parasitic fitness parameters indicated that the sporulation ability,infection and spore survivability,expansion capacity,and potential pathogenicity were the most important parasitic fitness attributes of the tested races.Based on the establishment of extracted three principal components and a comprehensive factor score mathematical models,evaluations of the parasitic fitness attributes of tested races showed that the level of relative parasitic fitness of the tested six races was:CYR32(1.15)>TSA-9(0.95)>TSA-6(0.92)>CYR34(0.29)>CYR31(–1.54)>CYR33(–1.77).The results indicated that two Yr5-virulent races TSA-9 and TSA-6 possessed relative parasitic fitness higher than races CYR34,CYR31,and CYR33,but lower than race CYR32,and have potential risks in developing to be predominant races.Therefore,continual monitoring of both Yr5-virulent races,and their variants is needed.The use of wheat cultivars(lines)with Yr5 resistance gene singly in wheat breeding is essential for being avoided,and is suggested to combine with other effective stripe rust resistance genes.

Research Advances in New Race Ug99 of Puccinia graminis f.sp. tritici

This paper reviewed the research advances of Ug99 and its resistance breeding from the aspects of its discovery, race variation, pathogenicity, distribution, spread, exploration of relative resistant genes, linked molecular marker selection and resistance breeding strategies, to provide basis for comprehensive understanding of the new Puccinia graminis f. sp. tritici race Ug99 and its potential threat to wheat production. Ug99 is a new Puccinia grarninis f. sp. tritici race with high variability, strong pathogenicity and rapid spread speed, which is likely to cause global damages to world wheat production. We should strengthen the exploration and utilization of new resistance genes in wheat and relative species and breeding of new wheat varieties with durable resistance, to control and prevent damages caused by Ug99 and its variants.

A FIASCO-Based Approach for Detection and Diagnosis of Puccinia graminis f.sp.tritici in China

Stem or black rust of wheat, caused by the fungus Puccinia graminis Pers. f. sp. tritici Eriks.＆E. Henn. （Pgt）, has historically caused severe losses to wheat （Triticum aestivum L.） production worldwide. In the Fujian and Guangdong provinces of China, six moderate-to-severe epidemics of wheat stem rust have occurred, which caused destructive losses of wheat between 1949 and 1966, although these were brought under control by integrated management. A rapid and reliable detection of the pathogen will contribute to the accurate forecast and seasonal control of this disease. The objective of this study was to develop a diagnostic molecular marker generated from simple sequence repeats （SSR） for the early rapid identiifcation of P. graminis. The genomic DNA of P. graminis, Puccinia striiformis, Puccinia triticina and seven other species was ampliifed by a pair of SSR primers generated by the FIASCO （fast isolation by AFLP sequences containing repeats） enrichment protocol. The primer set Pgtw （f）/Pgtw （r） generated a polymorphic pattern displaying a 330-bp DNA fragment speciifc for P. graminis whereas no DNA fragment was obtained from other non-target wheat fungal pathogens. The detection limit of the primer was 1 ng DNA in a 25-mL PCR reaction. The SSR markers of P. graminis can also be used to detect the presence of latent hyphae in Pgt-infected wheat leaves as early as 30 h post-inoculation. A rapid approach to distinguish P. graminis from similar pathogenic fungi would be anticipated in further study.

Relationship between the Hypersensitive Response of Wheat to Blumeria graminis f. sp. tritici and Hydrogen Peroxide,Three Enzyme Activities Changes

[Objective] The research aimed to study the relationship between the hypersensitive response of wheat to Blumeria graminis f.sp.tritici and hydrogen peroxide,3 enzyme activities changes and lay the foundation for discussing the resistant physiological mechanism of wheat to B.graminis.[Method] Taking B.graminis Bgt 17 and Bgt 6 and wheat cultivar Yang 158 as test materials,the number of hypersensitive cells and activities of POD,PPO and SOD in wheat leaves treated by H2O2 were determined.[Result] The mastoid...

Virulence and Diversity of Blumeria graminis f.sp.tritici Populations in China

Wheat powdery mildew, caused by Blumeria graminis f. sp. tritici, is an important disease in China. To characterize the virulence and diversity of the pathogen, 1 082 isolates were obtained from 8 major wheat-growing regions during the spring growing season in 2011. The virulence test was performed by inoculation on detached leaves of 22 differential lines with known Pm genes. Frequencies of virulence on these genotypes ranged from 0 to 97.4%. None of the 1 082 isolates was compatible to Pm21 and less than 20.0%were virulent to the genotype carrying Pm13. In contrast, the virulence frequencies of each population was more than 50.0%to differentials carrying Pm1a, Pm3b, Pm3c, Pm3f, Pm5a, Pm6 and Pm8. In total, 1 028 pathotypes were detected, of which 984 were unique. Phenotypic diversity indices revealed a high level of diversity within populations. Genetic distance between different populations correlated signiifcantly with geographical distance （R2=0.494, P 0.001）. In addition, isolates from Xinjiang appear to form a separate group. Signiifcant positive or negative associations between alleles at pairs of virulence loci were detected in 57 allele pairs to Pm genes. Virulence and diversity of the 8 populations suggested that varieties with effective resistance gene combinations should be developed at a regional level.

Population Genetic Analysis of Blumeria graminis f. sp. tritici in Qinghai Province, China

To gain more precise information about molecular genetic variation for wild populations of Blumeria graminis f. sp. tritici from Qinghai Province, China, 38 single-colony isolates were purified from samples collected from Haidong District, Xining City and Hainan Tibetan Autonomous Prefecture in 2010. The virulence of 21 isolates among them was tested at seedling stage on 34 wheat cultivars（lines） carrying known powdery mildew（Pm） resistant genes. The results showed that V1 a, V3 a, V3 c, V3 e, V5 a, V6, V7, V8 and V19 had high virulence frequencies（〉75%）, indicating a wide distribution; and V1 c, V5 b, V12, V13, V16, V21, VXBD, V2＋6, V2＋Mld and V4＋8, with less distribution, appeared to be lower in frequencies（0-20%）. The Nei＇s gene diversity（H）, Shannon＇s information index（I） and the percentage of polymorphic loci（P） were 0.23, 0.35 and 67.65%, respectively, which revealed a virulent diversity. The results from single nucleotide polymorphisms（SNPs） of 38 isolates showed that three housekeeping genes were found to contain a total of 9 SNP sites. 10 haplotypes（H1-H10） were inferred from the concatenated sequences, with 1 haplotype（H1） comprising of over 55% of Qinghai population. Phylogenic analysis did not show obvious geographical subdivision between the isolates. A multilocus haplotype network presented a radial structure, with H1 in the central as an inferred ancestor. Using analysis of molecular variance（AMOVA）, we found 1.63% of the total variation was among populations and 98.37% within populations, with a low fixations index（FST=0.01634, P〈0.05）. This revealed a relatively high genetic diversity but a low genetic divergence in Qinghai population. Moreover, the molecular data on gene flow（Nm=6.32） confirmed the migration of pathogen populations among areas in Qinghai Province.

Identification of eight Berberis species from the Yunnan-Guizhou plateau as aecial hosts for Puccinia striiformis f.sp.tritici,the wheat stripe rust pathogen

Puccinia striiformis Westend.f.sp.tritici Erikss.(Pst)infects wheat and causes stripe rust.The rust is heteroecious with wheat as the primary uredinial and telial host and barberry(Berberis spp.)as the alternate pycnial and aecial host.More than 40 Berberis species have been identified as alternate hosts for Pst,and most of these are Chinese Berberis species.However,little is known about Berberis species or their geographic distributions in the Yunnan-Guizhou plateau in southwestern China.The Yunnan-Guizhou plateau is considered to be an important and relatively independent region for the evolution of the wheat stripe rust pathogen in China because the entire disease cycle can be completed within the region.In this study,we conducted a survey of barberry plants in the Yunnan-Guizhou plateau and identified the eight Pst-susceptible Berberis species under controlled conditions,including B.julianae,B.tsienii,B.veitchii,B.wilsonae,B.wilsonae var.guhtzunica,B.franchetiana,B.lepidifolia and B.pruinosa.These species are reported here for the first time to serve as alternate hosts for the wheat stripe rust pathogen under controlled conditions.

Association Analysis of SP-SNPs and Avirulence Genes in Puccinia striiformis f. sp. tritici, the Wheat Stripe Rust Pathogen

Puccinia striiformis f. sp. tritici (Pst) is one of the pathogenic fungi on wheat, caused stripe rust that is a great threat for wheat production all over the world. Intensive efforts have been made to study genetics of wheat resistance to this disease, but few on avirulence of the pathogen due mainly to the nature of obligate biotrophism and the lack of systems for studying its genetics and molecular manipulations. To overcome these limitations, a natural Pst population comprising 352 isolates representative of a diverse virulence spectrum was genotyped using 97 secreted protein-single nucleotide polymorphism (SP-SNP) markers to identify candidate avirulence genes using association analysis. Among avirulence genes corresponding to 19 resistance genes, significantly associated SP-SNP markers were detected for avirulence genes AvYr1, AvYr2, AvYr6, AvYr7, AvYr8, AvYr44, AvYrExp2, AvYrSP, and AvYrTye. These results indicate that association analysis can be used to identify markers for avirulence genes. This study has laid the foundation for developing more SP-SNPs for mapping avirulence genes using segregating populations that can be generated through sexual reproduction on alternate hosts of the pathogen.

An improved method for RNA extraction from urediniospores of and wheat leaves infected by an obligate fungal pathogen, Puccinia striiformis f. sp. tritici

Stripe rust, caused by Puccinia striiformis f. sp. tritici, is an important wheat disease in China, seriously threatening wheat production. Understanding the winter survival of the fungus is a key for predicting the spring epidemics of the disease, which determines the crop loss. Estimation of P. striiformis f. sp. tritici winter survival requires processing a large number of samples for sensitive detection of the pathogen in wheat leaf tissue using real-time quantitative reverse transcription PCR （qRT-PCR）. A bottleneck for the analysis is the acquisition of a good yield of high quality RNA suitable for qRT-PCR to distinguish dead and alive fungal hyphae inside leaves. Although several methods have been described in the literatures and commercial kits are available for RNA extraction, these methods are mostly too complicated, expensive and inefficient. Thus, we modified three previously reported RNA extraction methods with common and low-cost reagents （LiCI, SDS and NaCI） to solve the problems and selected the best to obtain high quality and quantity RNA for use in qRT-PCR. In the three improved methods, the NaCI method was proven to be the best for extracting RNAfrom urediniospores of and wheat leaves infected by P. striiformis f. sp. tritici, although the modified LiCI and SDS methods also increased yield of RNA compared to the previous methods. The improved NaCI method has the following advantages： 1） Complete transfer of urediniospores of P. striiformis f. sp. tritici from the mortar and pestle can ensure the initial amount of RNA for the qRT-PCR analysis; 2） the use of low-cost NaCI to replace more expensive Trizol can reduce the cost; 3） the yield and quality of RNA can be increased; 4） the improved method is more suitable for a large number and high quantity of samples from fields. Using the improved NaCI method, the amount of RNA was increased three times from urediniospores of P. striiformis f. sp. tritici compared from the extraction kit. Approximately, 10.11 IJg total RNA of high quality was obtained from 100 mg of infected leaves, which was 8.8, 6.5, 3.4 and 2.1 folds of the amounts obtained from the previous LiCI, SDS, NaCI and traditional Trizol methods, respectively. The method could be used to study the overwintering rates of R striiformis f. sp. tritici over a large region of wheat production for predicting epidemic levels by determining pathogen survival levels after winter. The method can alsobe used in any studies which need a large number of high quality RNA samples.

Development of SSR Markers for a Phytopathogenic Fungus,Blumeria graminis f.sp.tritici,Using a FIASCO Protocol

Simple sequence repeats （SSR） have been widely used as molecular markers due to their abundance and high polymorphism, However, up to now, the SSR markers had not been developed in the obligate biotrophic phytopathogenic fungus, Blumeria graminis f.sp. tritici. From （AC）10 and （AG）10 enriched genomic libraries for Bgt, 25 primer pairs were designed using the FIASCO （fast isolation by AFLP of sequences containing repeats） protocol. Five primer pairs exhibited polymorphism with allelic diversity from two to seven alleles and produced 29 alleles in a survey of 90 isolates collected from six provinces （cities） in China, while the others displayed monomorphic. Levels of observed heterozygosity ranged from 0.000-0.044 （mean 0.025） and expected heterozygosity ranged from 0.297-0.816 （mean 0.538）. These molecular markers provide a novel source to genetic diversity assays and to genetic and physical mapping ofBgt. SSR markers of Bgt need to be further explored.

The TaFIM1 gene mediates wheat resistance against Puccinia striiformis f. sp. tritici and responds to abiotic stress

Fimbrin, a regulator of actin cytoskeletal dynamics that participates in numerous physiological and biochemical processes, controls multiple developmental processes in a variety of tissues and cell types. However, the role of fimbrin in pathogen defense of wheat and the mechanisms have not been well studied. Here, we investigated that the expression of TaFIM1 gene of wheat was significantly induced in response to avirulent race of Puccinia striiformis f. sp. tritici(Pst) and silencing of TaFIM1 by virus-induced gene silencing method. The results show that silencing of TaFIM1 resulted in a reduction of resistance against the stripe rust indicated by both phenotypes and a histological examination of Pst growth. Additionally, the expression level of Ta FIM1 gene was up-regulated under abiotic stresses. These findings suggest that Ta FIM1 functions as a positive regulator of pathogen resistance of wheat plants and response to abiotic stress. Our work may show new light on understanding the roles of fimbrin in wheat.

Effects of Different Cultivation Patterns of Wheat on Population Structure of Puccinia striiformis West.f. sp. tritici

The paper was to study the effects of different cultivation patterns( mix cultivation and monocultivation) of wheat on population structure of Puccinia striiformis West. f. sp. tritici in the fields. Five race-specific-markers( CY32,CY31,CY29,CY23 and Shuiyuan pathotype) were used to survey 113 infected samples collected from two cultivation patterns. The results indicated that frequency of race-specific-markers under monocultivation was higher than that under mix cultivation; the dominant race-specific-markers were CY32 and CY29 under monocultivation,and the frequency of detection were 81. 5% and 78. 5%,respectively. The dominant race-specific-markers were CY29 and Shuiyuan pathotype under mix cultivation,and the frequency of detection are 41. 7% and 18. 8%,respectively.Several race-specific-markers were detected in single infected leaf,and 41. 7% of infected single leaf were detected with more than two race-specific-markers,58. 3% of infected single leaf were detected with one race-specific-marker under mix cultivation pattern,while there were 75. 0% infected leaves with more than two race-specific-markers and 25. 0% infected single leaf detected with one race-specific-marker under monocultivation pattern. The results indicated that mix cultivation pattern of wheat can reduce races on single leaf,affect the distribution of races in infected leaves,and suppress the occurrence frequency of dominant races of P. striiformis in the fields significantly,subsequently reduced severity and prevalence of the disease.

Study Genetic Variation Using DNA Molecular Markers and Identification Physiological Races of Wheat Stripe （yellow） Rust Puccinia striiformis f.sp tritici during 2010-2014 in Some Regions of Syria

Yellow Rust （stripe） rust （Puccinia striiformis West. f. sp. tritici） is one of the most epidemic diseases infect wheat in cold and wet regions. In 1988, this disease caused a loss of seasonal production amounted 70% on wheat variety Mexipak in Syria, and recurrent infection in 2010, caused by a virulent race called Yr27, caused a considerable loss in the production of bread wheat cultivars （Cham 8, Cham 6 particularly） amounted 90%. Recently, 15 races of yellow rust had been addressed in Syria for seasons 2010-2014; 159E256, 166E254, 166E256, 255 E112, 0 E0, 64 E 6, 230 El50, 0 E 18, 198 El30, 166 El50, 102 El60, 128 E0, 126 El50, 214E150, and 6E16. The race 6E16 was the most frequent during the two seasons, while the race 255El12 was the most virulent, followed by the race 230E222 and the race 0E0 was the weakest one. This study revealed the presence of fourteen newly observed races in Syria. Molecular Variance Analysis of Molecular Variance （AMOVA） of 55 yellow rust Puccinia striiformis f.sp tritici isolates examined by Amplify Fragment Length Polymorphism （AFLP） revealed high genetic variation within population, and the dimensional scale analysis （MSD） and tree diagram showed that the Syrian yellow rust isolates were clustered in three groups： the first group contained isolates derived from durum wheat, the second one contained bread wheat isolates, but the third was made of isolates derived from both durum and bread wheat species.

Random Amplified Polymorphic DNA （RAPD） Analysis on Blumeria graminis f.sp. tritici Isolates Collected in Central Gansu Province, China

Twenty isolated strains of Blumeria graminis f.sp. tritici collected from central Gansu province were studied with random amplified polymorphic DNA （RAPD） analysis. PCR amplifications using nine random primers generated a total of 81 bands, of which, 54 were polymorphic. The total percentage of polymorphic bands varied from 50.0% to 88.9%. The average percentage based on RAPD patterns was approximately 66.7%, which indicated high heredity differentiation among isolates. Clustering analysis showed that the polymorphism of the twenty isolates was related to geographical origins but had little relationship with the physiological race.

Population Diversity of Puccinia graminis is Sustained Through Sexual Cycle on Alternate Hosts

A high degree of virulence diversity has been maintained in the population of Puccinia graminis f. sp. tritici （Pgt） in northwestern United States. Although Berberis vulgaris is present in the region and Pgt has been isolated from aecial infections on B. vulgaris, the population is too diverse to be explained by the limited presence of B. vulgaris alone. Since 2008, we have isolated P. graminis from aecial infections on fruits of Mahonia repens and Mahonia aquifolium from northwestern United States. These two native woody shrub species, widely distributed in western North America, were once classified as resistant to P. graminis based on artificial inoculations. By isolating P. graminis from aecia, we established that M. repens and M. aquifolium along with B. vulgaris （albeit infrequent） serve as the alternate hosts ofP. graminis in the region. The isolates of P. graminis from Mahonia of North America had diverse virulence patterns and most of the isolates could be differentiated on Morocco, Line E, Chinese Spring, Little Club, LMPG-6, Rusty, and other genotypes that are considered to be universally susceptible to most Pgt isolates. This discovery explained the persistence of virulence diversity of Pgt observed in isolates derived from uredinia on cereal crops in the region. In addition to cereal crops, uredinial stage of the P. graminis population is sustained by wild grasses, especially Elymus glaucus, a native grass sharing the same habitat with the rusted Mahonia spp. Although virulence to some important stem rust resistance genes was observed in some isolates derived from Mahonia of North America when tested against single stem rust resistance gene stocks, the overall virulence is very limited in these isolates. This is likely a result of limited selection pressure on the rust population. In contrast to northwestern United Sates, the Pgt population in east of the Rocky Mountains of North America has declined steadily with a single race, QFCSC, being predominant in the last decade. This decline is likely due to a combination of factors, of which a lack of sexual recombination in the region is perhaps the most important one.

High-throughput RNA sequencing reveals differences between the transcriptomes of the five spore forms of Puccinia striiformis f.sp.tritici,the wheat stripe rust pathogen

The devastating wheat stripe(yellow)rust pathogen,Puccinia striiformis f.sp.tritici(Pst),is a macrocyclic and heteroe-cious fungus.Pst produces urediniospores and teliospores on its primary host,wheat,and pycniospores and aeciospores are produced on its alternate hosts,barberry(Berberis spp.)or mahonia(Mahonia spp.).Basidiospores are developed from teliospores and infect alternate hosts.These five spore forms play distinct roles in Pst infection,disease development,and fungal survival,etc.However,the specific genes and mechanisms underlying these functional differences are largely unknown.In this study,we performed,for the first time in rust fungi,the deep RNA sequencing to examine the transcriptomic shift among all five Pst spore forms.Among a total of 29,591 identified transcripts,951 were specifically expressed in basidiospores,whereas 920,761,266,and 110 were specific for teliospores,pycniospores,aeciospores,and urediniospores,respectively.Additionally,transcriptomes of sexual spores,namely pycniospores and basidiospores,showed significant differences from those of asexual spores(urediniospores,teliospores,and aeciospores),and transcriptomes of urediniospores and aeciospores were more similar to each other than to the three other spore forms.Especially,the basidiospores and pycniospores which infected the berberis shows wide differences in the cell wall degrading-enzymes and mating and pheromone response genes.Besides,we also found that there are 6234 differential expressed genes between the urediniospores and pycniospores,while only have 3 genes have alternative splicing enents,suggesting that differential genes expression may make more contribution than AS.This comprehensive transcriptome profiling can substantially improve our understanding of the developmental biology of the wheat stripe rust fungus.

TaARPC5 is required for wheat defense signaling in response to infection by the stripe rust fungus

Numerous studies using a combination of confocal microscopic-and pharmacological-based approaches have demonstrated that the actin cytoskeleton dynamically responds to pathogen infection.Here,we observed that phalloidin treatment induced actin nucleation,resulting in enhanced resistance of wheat against the stripe rust pathogen Puccinia striiformis f.sp.tritici(Pst).To define the mechanism underpinning this process,we characterized a family of conserved actin-binding proteins,the actin related protein(ARP)family,which controls actin polymerization.Specifically,we identified and characterized a wheat ARPC gene(Ta ARPC5),which encodes a 136-amino acid protein containing a P16-Arc domain,the smallest subunit of the ARP2/3 complex.Ta ARPC5 m RNA accumulation was induced following the infection of plants with the avirulent Pst strain,and following the elicitation with flagellin(e.g.,flg22)as well.Subcellular localization analysis revealed that Ta ARPC5 is primarily localized to the cortical actin cytoskeleton,and its precise cellular localizations suggest the proximity to processes correlated with the actin-organelle interface.Upon treatment with virulent Pst,Ta ARPC5-knockdown plants exhibited a significant reduction in the expression of PTI-specific m RNAs.Conversely,we observed enhanced induction of reactive oxygen species(ROS)accumulation and a decrease in Ta CAT1 expression following infection with an incompatible Pst isolate.Together with yeast complementation assays,the current study demonstrates a role for Ta ARPC5 in resistance signaling in wheat against Pst infection by regulating the host actin cytoskeleton.

A small knottin-like peptide negatively regulates in wheat to stripe rust resistance during early infection of wheat

Although Blufensins(Bln)have important functions in the response of plants to biotic stress the precise functioning of Bln in wheat remains largely unknown.Here we isolated a Bln gene(TaBln4)from Suwon 11 infected by Puccinia striiformis f.sp.tritici(Pst).Expression of TaBln4 increased in host plants at the early stage of infection with a virulent Pst race(CYR31)but was unchanged in response to infection by an avirulent race(CYR23).Transcription levels of TaBln4 were also regulated by hormone and abiotic stresses.Expression of TaBln4 in tobacco leaves suppressed Bax-induced programmed cell death.Knockdown of TaBln4 by virus-induced gene silencing inhibited colonization of race CYR31 by increasing the accumulation of H2O2 and formation of hypersensitive responses(HR).Transient overexpression of TaBln4 by a transient overexpression system(BSMV-VOX)increased the susceptibility of wheat to CYR31.Results from bimolecular fluorescence complementation and pull-down assays demonstrated that TaBLN4 interacted with calmodulin.Taken together,our results suggest that TaBln4 negatively regulates resistance in wheat to Pst in a reactive oxygen species(ROS)-and HR-dependent manner.

The Puccinia striiformis effector Hasp98 facilitates pathogenicity by blocking the kinase activity of wheat TaMAPK4

The obligate biotrophic fungus Puccinia striiformis f.sp.tritici(Pst)employs virulence effectors to disturb host immunity and causes devastating stripe rust disease.However,our understanding of how Pst effectors regulate host defense responses remains limited.In this study,we determined that the Pst effector Hasp98,which is highly expressed in Pst haustoria,inhibits plant immune responses triggered by flg22or nonpathogenic bacteria.Overexpression of Hasp98 in wheat(Triticum aestivum)suppressed avirulent Pst-triggered immunity,leading to decreased H2O2accumulation and promoting P.striiformis infection,whereas stable silencing of Hasp98 impaired P.striiformis pathogenicity.Hasp98 interacts with the wheat mitogenactivated protein kinase TaMAPK4,a positive regulator of plant resistance to stripe rust.The conserved TEY motif of TaMAPK4 is important for its kinase activity,which is required for the resistance function.We demonstrate that Hasp98inhibits the kinase activity of TaMAPK4 and that the stable silencing of TaMAPK4 compromises wheat resistance against P.striiformis.These results suggest that Hasp98 acts as a virulence effector to interfere with the MAPK signaling pathway in wheat,thereby promoting P.striiformis infection.