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Ralph Hückelhoven - One of the best experts on this subject based on the ideXlab platform.
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Infection of barley with the parasitic fungus Blumeria graminis f.sp. hordei results in the induction of HvADH1 and HvADH2.
Plant signaling & behavior, 2011Co-Authors: Reinhard K. Proels, Wolfgang Westermeier, Ralph HückelhovenAbstract:Besides the established functions of alcohol dehydrogenase (ADH) in the flooding response and in seed and pollen metabolism there is increasing evidence for a role of the fermentative pathway in biotic interactions. We have recently shown that barley ADH may be involved in susceptibility to the parasitic fungus Blumeria graminis f.sp. hordei (Bgh). Here, the transcriptional regulation of the barley ADH genes HvADH1 and HvADH2 after challenge of susceptible barley leaves with Bgh is addressed. Bgh infection results in an induction of HvADH1 and HvADH2, whereas HvADH3 expression was not detectable in leaves. With the use of native polyacrylamide gels the iso-enzyme composition with and without challenge by Bgh was analyzed, showing an activation of HvADH1 and HvADH2 in Bgh treated leaves.
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Respiratory Burst Oxidase Homologue A of barley contributes to penetration by the powdery mildew fungus Blumeria graminis f. sp. hordei
Journal of experimental botany, 2006Co-Authors: Marco Trujillo, Lothar Altschmied, Patrick Schweizer, Karl-heinz Kogel, Ralph HückelhovenAbstract:Reactive oxygen intermediates (ROI) are closely related to defence reactions of plants against pathogens. A prominent role in the production of ROI has been attributed to the plant respiratory burst oxidase homologues (RBOH) of the human phagocyte GP91(phox). A barley RBOH, which encodes a putative superoxide (O2*-)) producing NADPH oxidase, is described here. Histochemical analysis of the barley-Blumeria graminis f. sp. hordei (Bgh) interaction showed that O(2*-) is produced locally at the site of penetration. In contrast, hydrogen peroxide (H2O2) is produced in non-penetrated cell wall appositions. A barley RBOHA cDNA was isolated and a minor induction of expression of RBOHA was observed during the interactions of barley with Bgh. Transient RNA interference-mediated gene silencing of HvRBOHA during the penetration process of Bgh led to an increase of basal penetration resistance. The results support a potential role of HvRBOHA in cellular accessibility to Blumeria graminis.
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Mechanistic and genetic overlap of barley host and non-host resistance to Blumeria graminis
Molecular plant pathology, 2004Co-Authors: Marco Trujillo, Karl-heinz Kogel, Rients E. Niks, Marcus Troeger, Ralph HückelhovenAbstract:SUMMARY Non-host resistance of barley to Blumeria graminis f.sp. tritici (Bgt), an inappropriate forma specialis of the grass powdery mildew fungus, is associated with formation of cell wall appositions (papillae) at sites of attempted fungal penetration and a hypersensitive cell death reaction (HR) of single attacked cells. Penetration resistance and HR are also typical features of race-non-specific and race-specific resistance of barley to the appropriate Blumeria graminis f.sp. hordei (Bgh), raising the question of whether genotypic differences in the cellular response of barley to Bgt are detectable. First, we analysed fungal penetration frequencies and HR in different barley accessions known to show altered non-host resistance. In genotypes with limited resistance to inappropriate cereal rust fungi, we concomitantly detected low penetration resistance to Bgt and significant differences of HR rates during attack from Bgt. Second, we tested barley mutants known to show altered host responses to Bgh. The rar1-mutation that suppresses many types of race-cultivar-specific resistances did not influence the non-host response of the Bgt-isolate used in this study. However, mutants of Ror1 and Ror2, two genes required for full race non-specific penetration resistance of mlo-barley to barley powdery mildew fungus, exhibited altered defence response to Bgt, including higher frequencies of fungal penetration. On these mutants, growth of the inappropriate fungus was arrested subsequent to penetration by HR. Together, the data show that barley defence response to the wheat powdery mildew fungus is determined by similar factors as race-specific and race-non-specific resistance to appropriate Bgh.
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The barley apoptosis suppressor homologue BAX inhibitor-1 compromises nonhost penetration resistance of barley to the inappropriate pathogen Blumeria graminis f. sp. tritici.
Molecular plant-microbe interactions : MPMI, 2004Co-Authors: Ruth Eichmann, Karl-heinz Kogel, Holger Schultheiss, Ralph HückelhovenAbstract:BAX inhibitor-1 (BI-1) proteins have been characterized as suppressors of programmed cell death in mammals and plants. The barley BI-1 is a suppressor of nonspecific background resistance and mlo-mediated penetration resistance to the biotrophic fungal pathogen Blumeria graminis f. sp. hordei when overexpressed in epidermal cells of barley. We report here that BI-1 expression is also slightly up-regulated during interaction with the inappropriate wheat pathogen Blumeria graminis f. sp. tritici. Significantly, overexpression of BI-1 in single epidermal cells of barley by microprojectile-mediated transformation rendered cells susceptible to penetration by inappropriate B. graminis f. sp. tritici. The degree of transgene-induced accessibility to B. graminis f. sp. tritici was thereby similar to the effect achieved by overexpression of the defense suppressor gene Mlo and could not be further enhanced by double expression of both BI-1 and Mlo. Confocal laser scanning microscopy was used to locate a functional green fluorescing GFP:BI-1 fusion protein in endomembranes and the nuclear envelope of barley epidermal cells. Together, enhanced expression of barley BI-1 suppresses penetration resistance to B. graminis f. sp. tritici, linking barley nonhost resistance with cell death regulation.
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Apoplastic pH signaling in barley leaves attacked by the powdery mildew fungus Blumeria graminis f. sp. hordei.
Molecular plant-microbe interactions : MPMI, 2004Co-Authors: Hubert H. Felle, Ralph Hückelhoven, Almut Herrmann, Stefan Hanstein, Karl-heinz KogelAbstract:To investigate apoplastic responses of barley (Hordeum vulgare L.) to the barley powdery mildew fungus Blumeria graminis f. sp. hordei, noninvasive microprobe techniques were employed. H(+)- and Ca(2+)-selective microprobes were inserted into open stomata of barley leaves inoculated with Blumeria graminis f. sp. hordei race A6 conidia. Resistance gene-mediated responses of barley genotype Ingrid (susceptible parent line) and the near-isogenic resistant Ingrid backcross lines (I-mlo5, I-Mla12, and I-Mlg) were continuously monitored from 20 min to 4 days after inoculation. The main events were categorized as short-term responses around 2 h after inoculation (hai), intermediate responses around 8 and 12 hai, and long-term responses starting between 21 and 24 hai. Short-term responses were rapid transient decreases of apoplastic H(+)- and Ca2+ activities that lasted minutes only. Kinetics were similar for all genotypes tested, and thus, these short-term responses were attributed as nonspecific first encounters of fungal surface material with the host plasma membrane. This is supported by the observation that a microinjected chitin oligomer (GlcNAc)8 yielded similar apoplastic alkalinization. Intermediate responses are trains of H+ (increase) spikes that, being different in susceptible Ingrid and penetration-resistant I-mlo5 (or I-Mlg), were interpreted as accompanying specific events of papillae formation. Long-term events were massive slow and long-lasting alkalinizations up to two pH units above control. Since these latter changes were only observed with near-isogenic hypersensitive reaction (HR)-mounting genotypes I-Mla12 and I-Mlg but not with I-mlo5 or, to a smaller extent, with susceptible Ingrid, both lacking significant rates of HR, they were rated as cell death specific. It is concluded that apoplastic pH changes are important indicators of host-pathogen interactions that correlate with both the different stages of fungal development and the different types of host defense response.
Karl-heinz Kogel - One of the best experts on this subject based on the ideXlab platform.
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Respiratory Burst Oxidase Homologue A of barley contributes to penetration by the powdery mildew fungus Blumeria graminis f. sp. hordei
Journal of experimental botany, 2006Co-Authors: Marco Trujillo, Lothar Altschmied, Patrick Schweizer, Karl-heinz Kogel, Ralph HückelhovenAbstract:Reactive oxygen intermediates (ROI) are closely related to defence reactions of plants against pathogens. A prominent role in the production of ROI has been attributed to the plant respiratory burst oxidase homologues (RBOH) of the human phagocyte GP91(phox). A barley RBOH, which encodes a putative superoxide (O2*-)) producing NADPH oxidase, is described here. Histochemical analysis of the barley-Blumeria graminis f. sp. hordei (Bgh) interaction showed that O(2*-) is produced locally at the site of penetration. In contrast, hydrogen peroxide (H2O2) is produced in non-penetrated cell wall appositions. A barley RBOHA cDNA was isolated and a minor induction of expression of RBOHA was observed during the interactions of barley with Bgh. Transient RNA interference-mediated gene silencing of HvRBOHA during the penetration process of Bgh led to an increase of basal penetration resistance. The results support a potential role of HvRBOHA in cellular accessibility to Blumeria graminis.
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Mechanistic and genetic overlap of barley host and non-host resistance to Blumeria graminis
Molecular plant pathology, 2004Co-Authors: Marco Trujillo, Karl-heinz Kogel, Rients E. Niks, Marcus Troeger, Ralph HückelhovenAbstract:SUMMARY Non-host resistance of barley to Blumeria graminis f.sp. tritici (Bgt), an inappropriate forma specialis of the grass powdery mildew fungus, is associated with formation of cell wall appositions (papillae) at sites of attempted fungal penetration and a hypersensitive cell death reaction (HR) of single attacked cells. Penetration resistance and HR are also typical features of race-non-specific and race-specific resistance of barley to the appropriate Blumeria graminis f.sp. hordei (Bgh), raising the question of whether genotypic differences in the cellular response of barley to Bgt are detectable. First, we analysed fungal penetration frequencies and HR in different barley accessions known to show altered non-host resistance. In genotypes with limited resistance to inappropriate cereal rust fungi, we concomitantly detected low penetration resistance to Bgt and significant differences of HR rates during attack from Bgt. Second, we tested barley mutants known to show altered host responses to Bgh. The rar1-mutation that suppresses many types of race-cultivar-specific resistances did not influence the non-host response of the Bgt-isolate used in this study. However, mutants of Ror1 and Ror2, two genes required for full race non-specific penetration resistance of mlo-barley to barley powdery mildew fungus, exhibited altered defence response to Bgt, including higher frequencies of fungal penetration. On these mutants, growth of the inappropriate fungus was arrested subsequent to penetration by HR. Together, the data show that barley defence response to the wheat powdery mildew fungus is determined by similar factors as race-specific and race-non-specific resistance to appropriate Bgh.
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The barley apoptosis suppressor homologue BAX inhibitor-1 compromises nonhost penetration resistance of barley to the inappropriate pathogen Blumeria graminis f. sp. tritici.
Molecular plant-microbe interactions : MPMI, 2004Co-Authors: Ruth Eichmann, Karl-heinz Kogel, Holger Schultheiss, Ralph HückelhovenAbstract:BAX inhibitor-1 (BI-1) proteins have been characterized as suppressors of programmed cell death in mammals and plants. The barley BI-1 is a suppressor of nonspecific background resistance and mlo-mediated penetration resistance to the biotrophic fungal pathogen Blumeria graminis f. sp. hordei when overexpressed in epidermal cells of barley. We report here that BI-1 expression is also slightly up-regulated during interaction with the inappropriate wheat pathogen Blumeria graminis f. sp. tritici. Significantly, overexpression of BI-1 in single epidermal cells of barley by microprojectile-mediated transformation rendered cells susceptible to penetration by inappropriate B. graminis f. sp. tritici. The degree of transgene-induced accessibility to B. graminis f. sp. tritici was thereby similar to the effect achieved by overexpression of the defense suppressor gene Mlo and could not be further enhanced by double expression of both BI-1 and Mlo. Confocal laser scanning microscopy was used to locate a functional green fluorescing GFP:BI-1 fusion protein in endomembranes and the nuclear envelope of barley epidermal cells. Together, enhanced expression of barley BI-1 suppresses penetration resistance to B. graminis f. sp. tritici, linking barley nonhost resistance with cell death regulation.
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Apoplastic pH signaling in barley leaves attacked by the powdery mildew fungus Blumeria graminis f. sp. hordei.
Molecular plant-microbe interactions : MPMI, 2004Co-Authors: Hubert H. Felle, Ralph Hückelhoven, Almut Herrmann, Stefan Hanstein, Karl-heinz KogelAbstract:To investigate apoplastic responses of barley (Hordeum vulgare L.) to the barley powdery mildew fungus Blumeria graminis f. sp. hordei, noninvasive microprobe techniques were employed. H(+)- and Ca(2+)-selective microprobes were inserted into open stomata of barley leaves inoculated with Blumeria graminis f. sp. hordei race A6 conidia. Resistance gene-mediated responses of barley genotype Ingrid (susceptible parent line) and the near-isogenic resistant Ingrid backcross lines (I-mlo5, I-Mla12, and I-Mlg) were continuously monitored from 20 min to 4 days after inoculation. The main events were categorized as short-term responses around 2 h after inoculation (hai), intermediate responses around 8 and 12 hai, and long-term responses starting between 21 and 24 hai. Short-term responses were rapid transient decreases of apoplastic H(+)- and Ca2+ activities that lasted minutes only. Kinetics were similar for all genotypes tested, and thus, these short-term responses were attributed as nonspecific first encounters of fungal surface material with the host plasma membrane. This is supported by the observation that a microinjected chitin oligomer (GlcNAc)8 yielded similar apoplastic alkalinization. Intermediate responses are trains of H+ (increase) spikes that, being different in susceptible Ingrid and penetration-resistant I-mlo5 (or I-Mlg), were interpreted as accompanying specific events of papillae formation. Long-term events were massive slow and long-lasting alkalinizations up to two pH units above control. Since these latter changes were only observed with near-isogenic hypersensitive reaction (HR)-mounting genotypes I-Mla12 and I-Mlg but not with I-mlo5 or, to a smaller extent, with susceptible Ingrid, both lacking significant rates of HR, they were rated as cell death specific. It is concluded that apoplastic pH changes are important indicators of host-pathogen interactions that correlate with both the different stages of fungal development and the different types of host defense response.
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Superoxide and Hydrogen Peroxide Play Different Roles in the Nonhost Interaction of Barley and Wheat with Inappropriate formae speciales of Blumeria graminis
Molecular plant-microbe interactions : MPMI, 2004Co-Authors: Marco Trujillo, Karl-heinz Kogel, Ralph HückelhovenAbstract:Nonhost resistance of cereals to inappropriate formae speciales of Blumeria graminis is little understood. However, on the microscopic level, nonhost defense to B. graminis is reminiscent of host defense preventing fungal development by penetration resistance and the hypersensitive cell death response (HR). We analyzed histochemically the accumulation of superoxide anion radicals (O2*-) and hydrogen peroxide (H2O2) at sites of B. graminis attack in nonhost barley and wheat. Superoxide visualized by subcellular reduction of nitroblue tetrazolium accumulated in association with successful fungal penetration in attacked cells and in cells neighboring HR. In contrast, H2O2 accumulated in cell wall appositions beneath fungal penetration attempts or in the entire epidermal cell during HR. The data provide evidence for different roles and sources of superoxide and H2O2 in the nonhost interaction of cereals with inappropriate formae speciales of B. graminis.
Timothy L. W. Carver - One of the best experts on this subject based on the ideXlab platform.
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Blumeria graminis interactions with barley conditioned by different single R genes demonstrate a temporal and spatial relationship between stomatal dysfunction and cell death
Phytopathology, 2010Co-Authors: Elena Prats, B. J. Thomas, Timothy L. W. Carver, Peter C. Roberts, Ruth Sanderson, Neil Paveley, Michael Foged Lyngkjær, Luis A. J. MurAbstract:Prats, E., Gay, A. P., Roberts, P. C., Thomas, B. J., Sanderson, R., l Paveley, N., Lyngkjaer, M. F., Carver, T. L. W., Mur, L. A. J. (2010). Blumeria graminis interactions with barley conditioned by different single R genes demonstrate a temporal and spatial relationship between stomatal dysfunction and cell death. Phytopathology, 100, (1), 21-32 IMPF: 02.42 RONO: 00 Sponsorship: Marie Curie European Reintegration Grant; Defra; ERDF interreg
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Pathogen-derived nitric oxide influences formation of the appressorium infection structure in the phytopathogenic fungus Blumeria graminis.
Research in microbiology, 2008Co-Authors: Elena Prats, Timothy L. W. Carver, Luis A. J. MurAbstract:Nitric oxide (NO) is an important signal in plant resistance to pathogens. Here we report that NO is also generated by Blumeria graminis f.sp. hordei as a pathogenesis determinant on barley. Infection by B. graminis f.sp. hordei is dependent on appressorium formation in order to penetrate the host. Using fluorescent dye diaminofluorescein-2 diacetate (DAF-2DA) and confocal laser scanning microscopy, transient NO generation was detected within the B. graminis f.sp. hordei appressorium during its maturation. To confirm that NO was indeed being measured, DAF-2DA fluorescence was suppressed using a NO scavenger and a mammalian NO synthase inhibitor. Both chemicals affected the number of appressorial lobes produced by the fungus. These data indicate that NO plays a key role in formation of B. graminis f.sp. hordei appressoria.
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Cellular basis of resistance to different formae speciales of Blumeria graminis in Hordeum chilense, wheat, and tritordeum and agroticum amphiploids
Canadian Journal of Plant Pathology, 2006Co-Authors: Elena Prats, Sara Fondevilla, Diego Rubiales, Timothy L. W. CarverAbstract:Tritordeum and agroticum amphiploids, derived from hybridization of Triticum species with Hordeum chilense or Agropyron cristatum, were assessed for resistance to Blumeria graminis. In glasshouse tests, all parental lines of H. chilense and A. cristatum showed complete resistance to wheat powdery mildew [Blumeria graminis f. sp. tritici] while all Triticum parents, except one, were highly susceptible. The amphiploids were all resistant to B. graminis f. sp. tritici, allowing the development of only a few sporulating colonies on leaves. Microscopic examination of host-cell responses to B. graminis revealed that resistance in H. chilense and amphiploids was attributable to two major factors: (i) a significant reduction in successful fungal penetration by rapid deposition of papillae in the host epidermal cell wall and (ii) a significant increase in frequency of death of penetrated epidermal cells. Papillae formation was associated with localized autofluorescence in host epidermal cells. Cell death prevented...
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Of genes and genomes, needles and haystacks: Blumeria graminis and functionality.
Molecular plant pathology, 2005Co-Authors: Ziguo Zhang, B. J. Thomas, Timothy L. W. Carver, Catherine Henderson, E. Perfect, Pari Skamnioti, Sarah J GurrAbstract:SUMMARY Here, we consider the barley powdery mildew fungus, Blumeria graminis (DC Speer) f.sp. hordei (Marchal), and review recent research which has added to our understanding of the biology and molecular biology which underpins the asexual life cycle of this potentially devastating pathogen. We focus on the early stages of the host-pathogen interaction and report current understanding in the areas of leaf perception, fungal signal transduction and host-imposed oxidative stress management. Through this, it is becoming increasingly clear how closely and subtly both sides of the relationship are regulated. Collectively, however, this review highlights the high degree of complexity in working with an obligate parasite. Our experiences suggest that we would make more efficient progress towards understanding the basis of susceptibility and resistance to this true obligate biotroph if its genome sequence was available.
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Expression of Resistance to Blumeria Graminis f.sp. Tritici in ‘Chinese Spring’ Wheat Addition Lines Containing Chromosomes from Hordeum Vulgare and H. Chilense
Hereditas, 2004Co-Authors: Diego Rubiales, Timothy L. W. Carver, A. MartínAbstract:Blumeria graminis f.sp. tritici (syn. Erysiphe gruminis f.sp. rritici ) causes an important disease of wheat (powdery mildew) to which Hordeum uulgare and H. chilense are resistant. The study of chromosomal addition lines of H. uulgare and H. chilense in wheat showed that they possessed resistance to wheat powdery mildew. This was expressed as a reduction of disease severity but it was not associated with increased macroscopically visible necrosis. The resistance is of broad genetic basis, conferred by gene(s) present on different chromosomes of both H. uulgure and H. chilense. The feasibility of transferring this resistance to wheat is discussed.
Thomas Wicker - One of the best experts on this subject based on the ideXlab platform.
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rapid turnover of effectors in grass powdery mildew Blumeria graminis
BMC Evolutionary Biology, 2017Co-Authors: Fabrizio Menardo, Thomas Wicker, Coraline R Praz, Beat KellerAbstract:Grass powdery mildew (Blumeria graminis, Ascomycota) is a major pathogen of cereal crops and has become a model organism for obligate biotrophic fungal pathogens of plants. The sequenced genomes of two formae speciales (ff.spp.), B.g. hordei and B.g. tritici (pathogens of barley and wheat), were found to be enriched in candidate effector genes (CEGs). Similar to other filamentous pathogens, CEGs in B. graminis are under positive selection. Additionally, effectors are more likely to have presence-absence polymorphisms than other genes among different strains. Here we identified effectors in the genomes of three additional host-specific lineages of B. graminis (B.g. poae, B.g. avenae and B.g. infecting Lolium) which diverged between 24 and 5 million years ago (Mya). We found that most CEGs in B. graminis are clustered in families and that most families are present in both reference genomes (B.g. hordei and B.g. tritici) and in the genomes of all three newly annotated lineages. We identified conserved protein domains including a novel lipid binding domain. The phylogenetic analysis showed that frequent gene duplications and losses shaped the diversity of the effector repertoires of the different lineages through their evolutionary history. We observed several lineage-specific expansions where large clades of CEGs originated in only one lineage from a single gene through repeated gene duplications. When we applied a birth-death model we found that the turnover rate (the rate at which genes are deleted and duplicated) of CEG families is much higher than for non-CEG families. The analysis of genomic context revealed that the immediate surroundings of CEGs are enriched in transposable elements (TE) which could play a role in the duplication and deletion of CEGs. The CEG repertoires of related pathogens diverged dramatically in short evolutionary times because of rapid turnover and of positive selection fixing non-synonymous mutations. While signatures of positive selection on effector sequences are the expected outcome of the evolutionary “arms race” between pathogen and plant immune system, it is more difficult to infer the mechanisms and evolutionary forces that maintained an extreme turnover rate in CEG families of B. graminis for several millions of years.
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Genetic and molecular characterization of a locus involved in avirulence of Blumeria graminis f. sp. tritici on wheat Pm3 resistance alleles.
Fungal genetics and biology : FG & B, 2015Co-Authors: Francis Parlange, Stefan Roffler, Fabrizio Menardo, Roi Ben-david, Salim Bourras, Kaitlin E. Mcnally, Simone Oberhaensli, Daniel Stirnweis, Gabriele Buchmann, Thomas WickerAbstract:Wheat powdery mildew is caused by the obligate biotrophic fungus Blumeria graminis f. sp. tritici. The allelic series of the wheat Pm3 gene conferring race-specific resistance against powdery mildew has been well characterized functionally, and recently the corresponding avirulence gene AvrPm3a/f triggering the specific recognition by Pm3a and Pm3f alleles was cloned. Here, we describe the genetic and molecular analysis of two additional Blumeria loci involved in the resistance mediated by the Pm3c and Pm3f alleles. We genetically identified the two loci and mapped at high resolution one locus involved in the avirulence towards both Pm3c and Pm3f. The single candidate gene Bcg1 was identified in a physical target interval of 26kb defined by flanking genetic markers. Bcg1 encodes a small secreted protein sharing structural homology with ribonucleases and belongs to a family of clustered putative effector genes under diversifying selection. We found a very good, but not complete, correlation of Bcg1 haplotypes with the phenotypes of natural isolates. Two mutants were generated that were affected in their phenotypes towards Pm3a and Pm3f but did not show any sequence polymorphism in Bcg1. Our results suggest that avirulence to Pm3 in Blumeria is determined by a complex network of genes, in which Bcg1 might have a central role as a modifier of the Pm3/AvrPm3 interactions.
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A major invasion of transposable elements accounts for the large size of the Blumeria graminis f. sp. tritici genome
Functional & integrative genomics, 2011Co-Authors: Francis Parlange, Simone Oberhaensli, Thomas Wicker, James Breen, Matthias Platzer, Stefan Taudien, Hana Šimková, Jaroslav Doležel, Beat KellerAbstract:Powdery mildew of wheat (Triticum aestivum L.) is caused by the ascomycete fungus Blumeria graminis f.sp. tritici. Genomic approaches open new ways to study the biology of this obligate biotrophic pathogen. We started the analysis of the Bg tritici genome with the low-pass sequencing of its genome using the 454 technology and the construction of the first genomic bacterial artificial chromosome (BAC) library for this fungus. High-coverage contigs were assembled with the 454 reads. They allowed the characterization of 56 transposable elements and the establishment of the Blumeria repeat database. The BAC library contains 12,288 clones with an average insert size of 115 kb, which represents a maximum of 7.5-fold genome coverage. Sequencing of the BAC ends generated 12.6 Mb of random sequence representative of the genome. Analysis of BAC-end sequences revealed a massive invasion of transposable elements accounting for at least 85% of the genome. This explains the unusually large size of this genome which we estimate to be at least 174 Mb, based on a large-scale physical map constructed through the fingerprinting of the BAC library. Our study represents a crucial step in the perspective of the determination and study of the whole Bg tritici genome sequence.
Marco Trujillo - One of the best experts on this subject based on the ideXlab platform.
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Respiratory Burst Oxidase Homologue A of barley contributes to penetration by the powdery mildew fungus Blumeria graminis f. sp. hordei
Journal of experimental botany, 2006Co-Authors: Marco Trujillo, Lothar Altschmied, Patrick Schweizer, Karl-heinz Kogel, Ralph HückelhovenAbstract:Reactive oxygen intermediates (ROI) are closely related to defence reactions of plants against pathogens. A prominent role in the production of ROI has been attributed to the plant respiratory burst oxidase homologues (RBOH) of the human phagocyte GP91(phox). A barley RBOH, which encodes a putative superoxide (O2*-)) producing NADPH oxidase, is described here. Histochemical analysis of the barley-Blumeria graminis f. sp. hordei (Bgh) interaction showed that O(2*-) is produced locally at the site of penetration. In contrast, hydrogen peroxide (H2O2) is produced in non-penetrated cell wall appositions. A barley RBOHA cDNA was isolated and a minor induction of expression of RBOHA was observed during the interactions of barley with Bgh. Transient RNA interference-mediated gene silencing of HvRBOHA during the penetration process of Bgh led to an increase of basal penetration resistance. The results support a potential role of HvRBOHA in cellular accessibility to Blumeria graminis.
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Mechanistic and genetic overlap of barley host and non-host resistance to Blumeria graminis
Molecular plant pathology, 2004Co-Authors: Marco Trujillo, Karl-heinz Kogel, Rients E. Niks, Marcus Troeger, Ralph HückelhovenAbstract:SUMMARY Non-host resistance of barley to Blumeria graminis f.sp. tritici (Bgt), an inappropriate forma specialis of the grass powdery mildew fungus, is associated with formation of cell wall appositions (papillae) at sites of attempted fungal penetration and a hypersensitive cell death reaction (HR) of single attacked cells. Penetration resistance and HR are also typical features of race-non-specific and race-specific resistance of barley to the appropriate Blumeria graminis f.sp. hordei (Bgh), raising the question of whether genotypic differences in the cellular response of barley to Bgt are detectable. First, we analysed fungal penetration frequencies and HR in different barley accessions known to show altered non-host resistance. In genotypes with limited resistance to inappropriate cereal rust fungi, we concomitantly detected low penetration resistance to Bgt and significant differences of HR rates during attack from Bgt. Second, we tested barley mutants known to show altered host responses to Bgh. The rar1-mutation that suppresses many types of race-cultivar-specific resistances did not influence the non-host response of the Bgt-isolate used in this study. However, mutants of Ror1 and Ror2, two genes required for full race non-specific penetration resistance of mlo-barley to barley powdery mildew fungus, exhibited altered defence response to Bgt, including higher frequencies of fungal penetration. On these mutants, growth of the inappropriate fungus was arrested subsequent to penetration by HR. Together, the data show that barley defence response to the wheat powdery mildew fungus is determined by similar factors as race-specific and race-non-specific resistance to appropriate Bgh.
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Superoxide and Hydrogen Peroxide Play Different Roles in the Nonhost Interaction of Barley and Wheat with Inappropriate formae speciales of Blumeria graminis
Molecular plant-microbe interactions : MPMI, 2004Co-Authors: Marco Trujillo, Karl-heinz Kogel, Ralph HückelhovenAbstract:Nonhost resistance of cereals to inappropriate formae speciales of Blumeria graminis is little understood. However, on the microscopic level, nonhost defense to B. graminis is reminiscent of host defense preventing fungal development by penetration resistance and the hypersensitive cell death response (HR). We analyzed histochemically the accumulation of superoxide anion radicals (O2*-) and hydrogen peroxide (H2O2) at sites of B. graminis attack in nonhost barley and wheat. Superoxide visualized by subcellular reduction of nitroblue tetrazolium accumulated in association with successful fungal penetration in attacked cells and in cells neighboring HR. In contrast, H2O2 accumulated in cell wall appositions beneath fungal penetration attempts or in the entire epidermal cell during HR. The data provide evidence for different roles and sources of superoxide and H2O2 in the nonhost interaction of cereals with inappropriate formae speciales of B. graminis.