TaAbc1, a Member of Abc1-Like Family Involved in Hypersensitive Response against the Stripe Rust Fungal Pathogen in Wheat

To search for genes involved in wheat (Triticum aestivum L.) defense response to the infection of stripe rust pathogen Puccinia striiformis f. sp. tritici (Pst), we identified and cloned a new wheat gene similar to the genes in the Abc1-like gene family. The new gene, designated as TaAbc1, encodes a 717-amino acid, 80.35 kD protein. The TaAbc1 protein contains two conserved domains shared by Abc1-like proteins, two trans-membrane domains at the C-terminal, and a 36-amino acid chloroplast targeting presequence at the N-terminal. Characterization of TaAbc1 expression revealed that gene expression was tissue-specific and could be up-regulated by biotic agents (e.g., stripe rust pathogen) and/or by an abiotic stress like wounding. High-fold induction was associated with the hypersensitive response (HR) triggered only by avirulent stripe rust pathotypes, suggesting that TaAbc1 is a rust-pathotype specific HR-mediator. Down-regulating TaAbc1 reduced HR but not the overall resistance level in Suwon11 to CYR23, suggesting TaAbc1 was involved in HR against stripe rust, but overall host resistance is not HR-dependent.     

Identification and genetic mapping of a recessive gene for resistance to stripe rust in wheat line LM168-1

Stripe rust (or yellow rust), caused by the fungus Puccinia striiformis f. sp. tritici (Pst), is one of the most important foliar diseases of wheat. Characterization and utilization of novel resistant genes is the most effective, economic and environmentally friendly approach to controlling the disease. Wheat line LM168-1, which was derived from a cross between common wheat Chuannong 16 and Milan, has good adult-plant resistance to stripe rust, based on field tests over several years. To elucidate the genetic basis of resistance, LM168-1 was crossed with susceptible variety SY95-71. Parents and F1, F2, BC1 and F2:3 progenies were tested in 2009–2011 in a field inoculated with the predominant races of Pst in China. The genetic analysis showed that resistance to stripe rust in LM168-1 was controlled by a single recessive gene, temporarily designated yrLM168. Simple sequence repeat (SSR), resistance gene analog polymorphism (RGAP) and target region amplification polymorphism (TRAP) techniques were used to identify molecular markers linked to the resistance locus. Finally, a linkage group consisting of two SSR, four RGAP and five TRAP markers was constructed for yrLM168 with 102 F2 plants. The closest markers R1 and R2 flanked the resistance gene locus at 2.4 and 2.4 cM, respectively. Furthermore, two SSR markers Xwmc59 and Xwmc145 assigned the gene to chromosome 6A. Because yrLM168 confers high-level resistance to the predominant races of Pst in China, it should be useful in stripe rust resistance breeding programs. The closely linked markers can be used for rapidly transferring yrLM168 to wheat breeding populations.     

小麦锌指蛋白基因TaLOL2的克隆及特征分析

通过电子克隆与RT-PCR相结合的方法,在条锈菌诱导的小麦叶片中克隆获得1个新的LSD1型锌指蛋白基因TaLOL2,并用qRT-PCR技术分析了其转录表达特征。结果显示:(1)小麦锌指蛋白基因TaLOL2的cDNA全长1 095bp,编码179个氨基酸。(2)TaLOL2含有3个典型的zf-LSD1型(CxxCxRxxLMYxxGASxVxCxxC)保守结构域,与水稻、拟南芥、大麦等植物LSD1型锌指蛋白序列具有高度相似性,其中与水稻OsLOL2相似度达86.0%。(3)进化树分析表明,TaLOL2与水稻、拟南芥和大麦中部分含有3个保守zf-LSD1锌指结构的基因亲缘关系较近,而与其它包含不同数目的zf-LSD1锌指结构的基因亲缘关系较远。(4)qRT-PCR定量分析表明,TaLOL2在条锈菌侵染前期呈上调表达,在亲和及非亲和反应中差异表达。研究表明,TaLOL2参与了条锈菌诱导的小麦抗病防卫反应,很可能作为正调控因子参与了小麦-条锈菌非亲和互作中对条锈菌的抗性信号途径。     

Population genetic diversity of Puccinia striiformis f. sp. tritici on different wheat varieties in Tianshui, Gansu Province

Population genetic diversity in Tianshui city was analyzed with SSR markers in 605 single-pustule isolates of the stripe rust pathogen, Puccinia striiformis f. sp. tritici (Pst), obtained from 19 varieties of wheat. Significant differences in genetic diversity among populations were defected. Genetic diversity was highest in population on Tian 863-13, a highly resistant variety, whereas genetic diversity was lowest in population on Huixianhong, a highly susceptible variety. Seven populations from seven varieties that carried the common Yr18 resistance gene were clustered as one sub-group at 0.88 similarity coefficient, which showed that resistance gene selection had close relation with pathogen??s component. The results of present study can provide a theoretical basis for integrated management of wheat stripe rust and effective deployment of resistance genes in Pst over-summering zones in China.     

Genome-Wide Association Mapping for Seedling and Adult Plant Resistance to Stripe Rust in Synthetic Hexaploid Wheat

Use of genetic diversity from related wild and domesticated species has made a significant contribution to improving wheat productivity. Synthetic hexaploid wheats (SHWs) exhibit natural genetic variation for resistance and/or tolerance to biotic and abiotic stresses. Stripe rust caused by (Puccinia striiformis f. sp. tritici; Pst), is an important disease of wheat worldwide. To characterise loci conferring resistance to stripe rust in SHWs, we conducted a genome-wide association study (GWAS) with a panel of 181 SHWs using the wheat 9K SNP iSelect array. The SHWs were evaluated for their response to the prevailing races of Pst at the seedling and adult plant stages, the latter in replicated field trials at two sites in Ethiopia in 2011. About 28% of the SHWs exhibited immunity at the seedling stage while 56% and 83% were resistant to Pst at the adult plant stage at Meraro and Arsi Robe, respectively. A total of 27 SNPs in nine genomic regions (1BS, 2AS, 2BL, 3BL, 3DL, 5A, 5BL, 6DS and 7A) were linked with resistance to Pst at the seedling stage, while 38 SNPs on 18 genomic regions were associated with resistance at the adult plant stage. Six genomic regions were commonly detected at both locations using a mixed linear model corrected for population structure, kinship relatedness and adjusted for false discovery rate (FDR). The loci on chromosome regions 1AS, 3DL, 6DS and 7AL appeared to be novel QTL; our results confirm that resynthesized wheat involving its progenitor species is a rich source of new stripe (yellow) rust resistance that may be useful in choosing SHWs and incorporating diverse yellow rust (YR) resistance loci into locally adapted wheat cultivars.     

A Novel Fungal Hyperparasite of Puccinia striiformis f. sp. tritici,the Causal Agent of Wheat Stripe Rust

Puccinia striiformis f. sp. tritici (Pst), the causal fungus of wheat stripe rust, was previously reported to be infected by Lecanicillium lecanii, Microdochium nivale and Typhula idahoensis. Here, we report a novel hyperparasite on Pst. This hyperparasitic fungus was identified as Cladosporium cladosporioides (Fresen.) GA de Vries based on morphological characteristics observed by light and scanning electron microscopy together with molecular data. The hyperparasite reduced the production and viability of urediniospores and, therefore, could potentially be used for biological control of wheat stripe rust.     

Genetic and Molecular Mapping of Stripe Rust Resistance Genes in Wheat Cultivar Zhongliang 12

Stripe rust, caused by Puccinia striiformis f.sp. tritici (Pst), is one of the most widespread and destructive diseases of wheat worldwide. Resistance breeding is constantly pursued for decades to tackle the variations of prevalent Pst races. Zhongliang 12 has strong resistance to abiotic stresses, wide adaptability, higher resistance to stripe rust and excellent biological characteristics. To identify the resistance gene(s) against stripe rust, Zhongliang 12 was crossed with stripe rust susceptible genotype Mingxian 169, and F₁, F₂, F_2 : 3 and BC₁ progenies were tested with Chinese Pst race CYR30 and CYR31 in seedling stage in greenhouse. Zhongliang 12 possessed different dominant genes for resistance to each race. Linkage maps were constructed with four simple sequence repeats (SSRs) markers, Xwmc695, Xcfd20, Xbarc121 and Xbarc49, for the gene on wheat chromosome 7AL conferring resistance to CYR30 (temporarily designated as Yrzhong12‐1) with genetic distance ranging from 3.1 to 10.8 cM and four SSR markers, Xpsp3003, Xcfd2129, Xwmc673 and Xwmc51, for the gene on wheat chromosome 1AL conferring resistance to CYR31 (temporarily designated as Yrzhong12‐2) with genetic distance ranging from 3.9 cM to 9.3 cM. The molecular markers closely linked to each gene should be useful in marker‐assisted selection in breeding programmes for against stripe rust.     

Genetic analysis and molecular mapping of a stripe rust resistance gene derived from Psathynrostachys huashanica Keng in wheat line H9014-121-5-5-9

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most devastating diseases worldwide and is also an important disease in China. The wheat translocation line H9014-121-5-5-9 was originally developed from interspecific hybridization between wheat (Triticum aestivum L.) line 7182 and Psathyrostachys huashanica Keng. This translocation line showed resistance to predominant stripe rust races in China when it was tested with nine races of Pst. To determine the inheritance and map the resistance gene, segregating populations were developed from the cross between H9014-121-5-5-9 and the susceptible cultivar Mingxian 169. The seedlings of the F1, F2, and F2:3 generations were tested with race CYR31. The results showed that the resistance in H9014-121-5-5-9 was conferred by a single dominant gene. Bulked segregant analysis and simple sequence repeat (SSR) markers were used to identify polymorphic markers associated with the resistance gene locus. Seven polymorphic SSR markers were linked to the resistance gene. A linkage map was constructed according to the genotypes of the seven SSR markers and the resistance gene. Based on the SSR marker positions on the wheat chromosome, the resistance gene was assigned on chromosome 1AL, temporarily designated YrHA. Based on chromosomal location, reaction patterns and pedigree analysis, YrHA should be a novel resistance gene to stripe rust. The molecular markers of the new resistance gene in H9014-121-5-5-9 could be useful for marker-assisted selection in breeding programs against stripe rust.     

TaLHY,a 1R-MYB Transcription Factor,Plays an Important Role in Disease Resistance against Stripe Rust Fungus and Ear Heading in Wheat

LHY (late elongated hypocotyl) is an important gene that regulates and controls biological rhythms in plants. Additionally, LHY is highly expressed in the SSH (suppression subtractive hybridization) cDNA library-induced stripe rust pathogen (CYR32) in our previous research. To identify the function of the LHY gene in disease resistance against stripe rust, we used RACE-PCR technology to clone TaLHY in the wheat variety Chuannong19. The cDNA of TaLHY is 3085 bp long with an open reading frame of 1947 bp. TaLHY is speculated to encode a 70.3 kDa protein of 648 amino acids , which has one typical plant MYB-DNA binding domain; additionally, phylogenetic tree shows that TaLHY has the highest homology with LHY of Brachypodium distachyon(BdLHY-like). Quantitative fluorescence PCR indicates that TaLHY has higher expression in the leaf, ear and stem of wheat but lower expression in the root. Infestation of CYR32 can result in up-regulated expression of TaLHY, peaking at 72 h. Using VIGS (virus-induced gene silencing) technology to disease-resistant wheat in the fourth leaf stage, plants with silenced TaLHY cannot complete their heading stage. Through the compatible interaction with the stripe rust physiological race CYR32, Chuannong 19 loses its immune capability toward the stripe rust pathogen, indicating that TaLHY may regulate and participate in the heading of wheat, as well as the defense responses against stripe rust infection.     

The RLK protein TaCRK10 activates wheat high-temperature seedling-plant resistance to stripe rust through interacting with TaH2A.1

Plants sense various pathogens and activate immunity responses through receptor-like kinases (RLKs). Cysteine-rich receptor-like kinases (CRKs) are involved in massive transduction pathways upon perception of a pathogen. However, the roles of CRKs in response to stripe rust are unclear. In the present study, we identified a CRK gene (designated TaCRK10) from wheat variety Xiaoyan 6 (XY6) that harbors high-temperature seedling-plant (HTSP) resistance to stripe rust caused by fungal pathogen Puccinia striiformis f. sp. tritici (Pst). The expression level of TaCRK10 was induced by Pst inoculation and high temperature treatment. Knockdown of TaCRK10 by virus-induced gene silencing resulted in attenuated wheat HTSP resistance to Pst, whereas there is no effect on Pst development and host responses under normal temperatures. Notably, overexpression of TaCRK10 in susceptible variety Fielder provided resistance only under normal temperatures at 14 days with reactive oxygen species accumulation and defense-related gene expression of the salicylic acid pathway. Moreover, TaCRK10 physically interacted with and phosphorylated a histone variant TaH2A.1, which belongs to the H2A.W group. Silencing of TaH2A.1 suppressed wheat resistance to Pst, indicating that TaH2A.1 plays a positive role in wheat resistance to Pst. Thus, TaCRK10 serves as an important sensor of Pst infection and high temperatures, and it activates wheat resistance to Pst through regulating nuclear processes. This knowledge helps elucidate the molecular mechanism of wheat HTSP resistance to Pst and promotes efforts in developing wheat varieties with resistance to stripe rust.     

Genome-Wide Association Mapping for Resistance to Leaf and Stripe Rust in Winter-Habit Hexaploid Wheat Landraces

Leaf rust, caused by Puccinia triticina (Pt), and stripe rust, caused by P. striiformis f. sp. tritici (Pst), are destructive foliar diseases of wheat worldwide. Breeding for disease resistance is the preferred strategy of managing both diseases. The continued emergence of new races of Pt and Pst requires a constant search for new sources of resistance. Here we report a genome-wide association analysis of 567 winter wheat (Triticum aestivum) landrace accessions using the Infinium iSelect 9K wheat SNP array to identify loci associated with seedling resistance to five races of Pt (MDCL, MFPS, THBL, TDBG, and TBDJ) and one race of Pst (PSTv-37) frequently found in the Northern Great Plains of the United States. Mixed linear models identified 65 and eight significant markers associated with leaf rust and stripe rust, respectively. Further, we identified 31 and three QTL associated with resistance to Pt and Pst, respectively. Eleven QTL, identified on chromosomes 3A, 4A, 5A, and 6D, are previously unknown for leaf rust resistance in T. aestivum.     

Characterization of protein kinase PsSRPKL,a novel pathogenicity factor in the wheat stripe rust fungus

As in other eukaryotes, protein kinases (PKs) are generally evolutionarily conserved and play major regulatory roles in plant pathogenic fungi. Many PKs have been proven to be important for pathogenesis in model fungal plant pathogens, but little is currently known about their roles in the pathogenesis of cereal rust fungi, devastating pathogens in agriculture worldwide. Here, we report on an in planta highly induced PK gene PsSRPKL from the wheat stripe rust fungus Puccinia striiformis f. sp. tritici (Pst), one of the most important cereal rust fungi. PsSRPKL belongs to a group of PKs that are evolutionarily specific to cereal rust fungi. It shows a high level of intraspecies polymorphism in the kinase domains and directed green fluorescent protein chimers to plant nuclei. Overexpression of PsSRPKL in fission yeast induces aberrant cell morphology and a decreased resistance to environmental stresses. Most importantly, PsSRPKL is proven to be an important pathogenicity factor responsible for fungal growth and responses to environmental stresses, therefore contributing significantly to Pst virulence in wheat. We hypothesize that cereal rust fungi have developed specific PKs as pathogenicity factors for adaptation to their host species during evolution. Thus, our findings provide significant insights into pathogenicity and virulence evolution in cereal rust fungi.     

Molecular mapping of Yr53, a new gene for stripe rust resistance in durum wheat accession PI 480148 and its transfer to common wheat

Stripe rust, caused by Puccinia striiformis f. sp. tritici (Pst), is one of the most damaging diseases of wheat worldwide. It is essential to identify new genes for effective resistance against the disease. Durum wheat PI 480148, originally from Ethiopia, was resistant in all seedling tests with several predominant Pst races in the US under controlled greenhouse conditions and at multiple locations subject to natural infection for several years. To map the resistance gene(s) and to transfer it to common wheat, a cross was made between PI 480148 and susceptible common wheat genotype Avocet S (AvS). Resistant F₃ plants with 42 chromosomes were selected cytologically and by testing with Pst race PST-100. A total of 157 F₄ plants from a single F₃ plant with 2n = 42 tested with PST-100 segregated in a 3 resistant: 1 susceptible ratio, indicating that a single dominant gene from PI 480148 conferred resistance. Using the F_3:4 population and the resistance gene-analog polymorphism (RGAP) and simple sequence repeat (SSR) markers, the gene was mapped to the long arm of chromosome 2B. SSR marker Xwmc441 and RGAP marker XLRRrev/NLRRrev ₃₅₀ flanked the resistance gene by 5.6 and 2.7 cM, respectively. The effective resistance of the gene to an Australian Pst isolate virulent to Yr5, which is also located on 2BL and confers resistance to all US Pst races, together with an allelism test of the two genes, indicated that the gene from PI 480148 is different from Yr5 and should be a new and useful gene for resistance to stripe rust. Resistant common wheat lines with plant types similar to AvS were selected for use in breeding programs.     

Remapping of the stripe rust resistance gene <Emphasis Type="Italic">Yr10</Emphasis> in common wheat

Key message

Yr10 is an important gene to control wheat stripe rust, and the search for Yr10 needs to be continued.

Abstract

Wheat stripe rust or yellow rust is a devastating fungal disease caused by Puccinia striiformis f. sp. tritici (Pst). Host disease resistance offers a primary source for controlling wheat stripe rust. The stripe rust resistance gene Yr10 confers the race-specific resistance to most tested Pst races in China including CYR29. Early studies proposed that Yr10 was a nucleotide-binding site, leucine-rich repeat gene archived as GenBank accession AF149112 (hereafter designated the Yr10 candidate gene or Yr10 _CG ). In this study, we revealed that 15 Chinese wheat cultivars positive for Yr10 _CG are susceptible to CYR29. We then expressed the Yr10 _CG cDNA in the common wheat ‘Bobwhite’. The Yr10 _CG -cDNA positive transgenic plants were also susceptible to CYR29. Thus, it is highly unlikely that Yr10 _CG corresponds to the Yr10 resistance gene. Using the Yr10 donor ‘Moro’ and the Pst-susceptible wheat ‘Huixianhong’, we generated two F₃ populations that displayed a single Mendelian segregation on the Yr10 gene, and used them to remap the Yr10 gene. Six markers were placed in the Yr10 region, with the Yr10 _CG gene now mapping about 1.2-cM proximal to the Yr10 locus and the Xsdauw79 marker is completely linked to the Yr10 locus. Apparently, the Yr10 gene has not yet been identified. Fine mapping and positional cloning of Yr10 is important for gene pyramiding for stripe rust resistance in wheat.