The Experts below are selected from a list of 360 Experts worldwide ranked by ideXlab platform

Gregory J. Lawrence - One of the best experts on this subject based on the ideXlab platform.

  • crystal structure of the Melampsora lini effector avrp reveals insights into a possible nuclear function and recognition by the flax disease resistance protein p
    Molecular Plant Pathology, 2018
    Co-Authors: Xiaoxiao Zhang, Ann-maree Catanzariti, Nadya Farah, Laura Rolston, Daniel J Ericsson, Maud Bernoux, Katerina Bendak, Chunhong Chen, Joel P Mackay, Gregory J. Lawrence
    Abstract:

    The effector protein AvrP is secreted by the flax rust fungal pathogen (Melampsora lini) and recognized specifically by the flax (Linum usitatissimum) P disease resistance protein, leading to effector-triggered immunity. To investigate the biological function of this effector and the mechanisms of specific recognition by the P resistance protein, we determined the crystal structure of AvrP. The structure reveals an elongated zinc-finger-like structure with a novel interleaved zinc-binding topology. The residues responsible for zinc binding are conserved in AvrP effector variants and mutations of these motifs result in a loss of P-mediated recognition. The first zinc-coordinating region of the structure displays a positively charged surface and shows some limited similarities to nucleic acid-binding and chromatin-associated proteins. We show that the majority of the AvrP protein accumulates in the plant nucleus when transiently expressed in Nicotiana benthamiana cells, suggesting a nuclear pathogenic function. Polymorphic residues in AvrP and its allelic variants map to the protein surface and could be associated with differences in recognition specificity. Several point mutations of residues on the non-conserved surface patch result in a loss of recognition by P, suggesting that these residues are required for recognition.

  • genome analysis and avirulence gene cloning using a high density radseq linkage map of the flax rust fungus Melampsora lini
    BMC Genomics, 2016
    Co-Authors: Claire Anderson, Gregory J. Lawrence, Adrienne R. Hardham, Adnane Nemri, Ann-maree Catanzariti, Muhammad Adil Khan, Cameron Jack, Narayana M Upadhyaya, Jeffrey G Ellis
    Abstract:

    Rust fungi are an important group of plant pathogens that cause devastating losses in agricultural, silvicultural and natural ecosystems. Plants can be protected from rust disease by resistance genes encoding receptors that trigger a highly effective defence response upon recognition of specific pathogen avirulence proteins. Identifying avirulence genes is crucial for understanding how virulence evolves in the field. To facilitate avirulence gene cloning in the flax rust fungus, Melampsora lini, we constructed a high-density genetic linkage map using single nucleotide polymorphisms detected in restriction site-associated DNA sequencing (RADseq) data. The map comprises 13,412 RADseq markers in 27 linkage groups that together span 5860 cM and contain 2756 recombination bins. The marker sequences were used to anchor 68.9 % of the M. lini genome assembly onto the genetic map. The map and anchored assembly were then used to: 1) show that M. lini has a high overall meiotic recombination rate, but recombination distribution is uneven and large coldspots exist; 2) show that substantial genome rearrangements have occurred in spontaneous loss-of-avirulence mutants; and 3) identify the AvrL2 and AvrM14 avirulence genes by map-based cloning. AvrM14 is a dual-specificity avirulence gene that encodes a predicted nudix hydrolase. AvrL2 is located in the region of the M. lini genome with the lowest recombination rate and encodes a small, highly-charged proline-rich protein. The M. lini high-density linkage map has greatly advanced our understanding of virulence mechanisms in this pathogen by providing novel insights into genome variability and enabling identification of two new avirulence genes.

  • the genome sequence and effector complement of the flax rust pathogen Melampsora lini
    Frontiers in Plant Science, 2014
    Co-Authors: Adnane Nemri, Gregory J. Lawrence, Claire Anderson, Narayana M Upadhyaya, Jeffrey G Ellis, Diane G O Saunders, Joe Win, David A Jones, Sophien Kamoun, Peter N. Dodds
    Abstract:

    Rust fungi cause serious yield reductions on crops, including wheat, barley, soybean, coffee, and represent real threats to global food security. Of these fungi, the flax rust pathogen Melampsora lini has been developed extensively over the past 80 years as a model to understand the molecular mechanisms that underpin pathogenesis. During infection, M. lini secretes virulence effectors to promote disease. The number of these effectors, their function and their degree of conservation across rust fungal species is unknown. To assess this, we sequenced and assembled de novo the genome of M. lini isolate CH5 into 21,130 scaffolds spanning 189 Mbp (scaffold N50 of 31 kbp). Global analysis of the DNA sequence revealed that repetitive elements, primarily retrotransposons, make up at least 45% of the genome. Using ab initio predictions, transcriptome data and homology searches, we identified 16,271 putative protein-coding genes. An analysis pipeline was then implemented to predict the effector complement of M. lini and compare it to that of the poplar rust, wheat stem rust and wheat stripe rust pathogens to identify conserved and species-specific effector candidates. Previous knowledge of four cloned M. lini avirulence effector proteins and two basidiomycete effectors was used to optimise parameters of the effector prediction pipeline. Markov clustering based on sequence similarity was performed to group effector candidates from all four rust pathogens. Clusters containing at least one member from M. lini were further analysed and prioritized based on features including expression in isolated haustoria and infected leaf tissue and conservation across rust species. Herein, we describe 200 of 940 clusters that ranked highest on our priority list, representing 725 flax rust candidate effectors. Our findings on this important model rust species provide insight into how effectors of rust fungi are conserved across species and how they may act to promote infection on their hosts.

  • internalization of flax rust avirulence proteins into flax and tobacco cells can occur in the absence of the pathogen
    The Plant Cell, 2010
    Co-Authors: Maryam Rafiqi, Gregory J. Lawrence, Adrienne R. Hardham, Jeffrey G Ellis, David A Jones, Pamela H P Gan, Michael Ravensdale, Peter N. Dodds
    Abstract:

    Translocation of pathogen effector proteins into the host cell cytoplasm is a key determinant for the pathogenicity of many bacterial and oomycete plant pathogens. A number of secreted fungal avirulence (Avr) proteins are also inferred to be delivered into host cells, based on their intracellular recognition by host resistance proteins, including those of flax rust (Melampsora lini). Here, we show by immunolocalization that the flax rust AvrM protein is secreted from haustoria during infection and accumulates in the haustorial wall. Five days after inoculation, the AvrM protein was also detected within the cytoplasm of a proportion of plant cells containing haustoria, confirming its delivery into host cells during infection. Transient expression of secreted AvrL567 and AvrM proteins fused to cerulean fluorescent protein in tobacco (Nicotiana tabacum) and flax cells resulted in intracellular accumulation of the fusion proteins. The rust Avr protein signal peptides were functional in plants and efficiently directed fused cerulean into the secretory pathway. Thus, these secreted effectors are internalized into the plant cell cytosol in the absence of the pathogen, suggesting that they do not require a pathogen-encoded transport mechanism. Uptake of these proteins is dependent on signals in their N-terminal regions, but the primary sequence features of these uptake regions are not conserved between different rust effectors.

  • transformation of the flax rust fungus Melampsora lini selection via silencing of an avirulence gene
    Plant Journal, 2009
    Co-Authors: Gregory J. Lawrence, Peter N. Dodds, Jeffrey G Ellis
    Abstract:

    Rust fungi cause devastating diseases on many important food crops, with a damaging stem rust epidemic currently affecting wheat production in Africa and the Middle East. These parasitic fungi propagate exclusively on plants, precluding the use of many biotechnological tools available for other culturable fungi. In particular the lack of a stable transformation system has been an impediment to the genetic manipulation required for molecular analysis of rust pathogenicity. We have developed an Agrobacterium-mediated genetic transformation procedure for the model flax rust fungus Melampsora lini, which infects flax (Linum usitatissimum). Selection of transgenic rust lines is based on silencing of AvrL567, which encodes a rust effector protein that is recognised by the flax L6 immune receptor. The non-transgenic rust line is unable to infect flax plants expressing L6, while silenced transgenic lines are virulent on these plants, providing an effective selection system. This directly confirms that the cloned AvrL567 gene is responsible for flax rust virulence phenotypes, and demonstrates the utility of this system to probe rust gene function.

Peter N. Dodds - One of the best experts on this subject based on the ideXlab platform.

  • Production of small cysteine-rich effector proteins in Escherichia coli for structural and functional studies.
    Molecular plant pathology, 2016
    Co-Authors: Xiaoxiao Zhang, Peter S. Solomon, Susan Breen, Megan A. Outram, Bostjan Kobe, Neal Nguyen, Peter N. Dodds, Simon J. Williams
    Abstract:

    Although the lifestyles and infection strategies of plant pathogens are diverse, a prevailing feature is the use of an arsenal of secreted proteins, known as effectors, which aid in microbial infection. In the case of eukaryotic filamentous pathogens, such as fungi and oomycetes, effector proteins are typically dissimilar, at the protein sequence level, to known protein families and functional domains. Consequently, we currently have a limited understanding of how fungal and oomycete effectors promote disease. Protein biochemistry and structural biology are two methods that can contribute greatly to the understanding of protein function. Both techniques are dependent on obtaining proteins that are pure and functional, and generally require the use of heterologous recombinant protein expression systems. Here, we present a general scheme and methodology for the production and characterization of small cysteine-rich (SCR) effectors utilizing Escherichia coli expression systems. Using this approach, we successfully produced cysteine-rich effectors derived from the biotrophic fungal pathogen Melampsora lini and the necrotrophic fungal pathogen Parastagonospora nodorum. Access to functional recombinant proteins facilitated crystallization and functional experiments. These results are discussed in the context of a general workflow that may serve as a template for others interested in understanding the function of SCR effector(s) from their plant pathogen(s) of interest.

  • the genome sequence and effector complement of the flax rust pathogen Melampsora lini
    Frontiers in Plant Science, 2014
    Co-Authors: Adnane Nemri, Gregory J. Lawrence, Claire Anderson, Narayana M Upadhyaya, Jeffrey G Ellis, Diane G O Saunders, Joe Win, David A Jones, Sophien Kamoun, Peter N. Dodds
    Abstract:

    Rust fungi cause serious yield reductions on crops, including wheat, barley, soybean, coffee, and represent real threats to global food security. Of these fungi, the flax rust pathogen Melampsora lini has been developed extensively over the past 80 years as a model to understand the molecular mechanisms that underpin pathogenesis. During infection, M. lini secretes virulence effectors to promote disease. The number of these effectors, their function and their degree of conservation across rust fungal species is unknown. To assess this, we sequenced and assembled de novo the genome of M. lini isolate CH5 into 21,130 scaffolds spanning 189 Mbp (scaffold N50 of 31 kbp). Global analysis of the DNA sequence revealed that repetitive elements, primarily retrotransposons, make up at least 45% of the genome. Using ab initio predictions, transcriptome data and homology searches, we identified 16,271 putative protein-coding genes. An analysis pipeline was then implemented to predict the effector complement of M. lini and compare it to that of the poplar rust, wheat stem rust and wheat stripe rust pathogens to identify conserved and species-specific effector candidates. Previous knowledge of four cloned M. lini avirulence effector proteins and two basidiomycete effectors was used to optimise parameters of the effector prediction pipeline. Markov clustering based on sequence similarity was performed to group effector candidates from all four rust pathogens. Clusters containing at least one member from M. lini were further analysed and prioritized based on features including expression in isolated haustoria and infected leaf tissue and conservation across rust species. Herein, we describe 200 of 940 clusters that ranked highest on our priority list, representing 725 flax rust candidate effectors. Our findings on this important model rust species provide insight into how effectors of rust fungi are conserved across species and how they may act to promote infection on their hosts.

  • structural and functional analysis of a plant resistance protein tir domain reveals interfaces for self association signaling and autoregulation
    Cell Host & Microbe, 2011
    Co-Authors: Maud Bernoux, Bostjan Kobe, Simon J. Williams, Xiaoxiao Zhang, Jeffrey G Ellis, Christopher Warren, Danny M Hatters, Eugene Valkov, Peter N. Dodds
    Abstract:

    The Toll/interleukin-1 receptor (TIR) domain occurs in animal and plant immune receptors. In the animal Toll-like receptors, homodimerization of the intracellular TIR domain is required for initiation of signaling cascades leading to innate immunity. By contrast, the role of the TIR domain in cytoplasmic nucleotide-binding/leucine-rich repeat (NB-LRR) plant immune resistance proteins is poorly understood. L6 is a TIR-NB-LRR resistance protein from flax (Linum usitatissimum) that confers resistance to the flax rust phytopathogenic fungus (Melampsora lini). We determine the crystal structure of the L6 TIR domain and show that, although dispensable for pathogenic effector protein recognition, the TIR domain alone is both necessary and sufficient for L6 immune signaling. We demonstrate that the L6 TIR domain self-associates, most likely forming a homodimer. Analysis of the structure combined with site-directed mutagenesis suggests that self-association is a requirement for immune signaling and reveals distinct surface regions involved in self-association, signaling, and autoregulation.

  • internalization of flax rust avirulence proteins into flax and tobacco cells can occur in the absence of the pathogen
    The Plant Cell, 2010
    Co-Authors: Maryam Rafiqi, Gregory J. Lawrence, Adrienne R. Hardham, Jeffrey G Ellis, David A Jones, Pamela H P Gan, Michael Ravensdale, Peter N. Dodds
    Abstract:

    Translocation of pathogen effector proteins into the host cell cytoplasm is a key determinant for the pathogenicity of many bacterial and oomycete plant pathogens. A number of secreted fungal avirulence (Avr) proteins are also inferred to be delivered into host cells, based on their intracellular recognition by host resistance proteins, including those of flax rust (Melampsora lini). Here, we show by immunolocalization that the flax rust AvrM protein is secreted from haustoria during infection and accumulates in the haustorial wall. Five days after inoculation, the AvrM protein was also detected within the cytoplasm of a proportion of plant cells containing haustoria, confirming its delivery into host cells during infection. Transient expression of secreted AvrL567 and AvrM proteins fused to cerulean fluorescent protein in tobacco (Nicotiana tabacum) and flax cells resulted in intracellular accumulation of the fusion proteins. The rust Avr protein signal peptides were functional in plants and efficiently directed fused cerulean into the secretory pathway. Thus, these secreted effectors are internalized into the plant cell cytosol in the absence of the pathogen, suggesting that they do not require a pathogen-encoded transport mechanism. Uptake of these proteins is dependent on signals in their N-terminal regions, but the primary sequence features of these uptake regions are not conserved between different rust effectors.

  • transformation of the flax rust fungus Melampsora lini selection via silencing of an avirulence gene
    Plant Journal, 2009
    Co-Authors: Gregory J. Lawrence, Peter N. Dodds, Jeffrey G Ellis
    Abstract:

    Rust fungi cause devastating diseases on many important food crops, with a damaging stem rust epidemic currently affecting wheat production in Africa and the Middle East. These parasitic fungi propagate exclusively on plants, precluding the use of many biotechnological tools available for other culturable fungi. In particular the lack of a stable transformation system has been an impediment to the genetic manipulation required for molecular analysis of rust pathogenicity. We have developed an Agrobacterium-mediated genetic transformation procedure for the model flax rust fungus Melampsora lini, which infects flax (Linum usitatissimum). Selection of transgenic rust lines is based on silencing of AvrL567, which encodes a rust effector protein that is recognised by the flax L6 immune receptor. The non-transgenic rust line is unable to infect flax plants expressing L6, while silenced transgenic lines are virulent on these plants, providing an effective selection system. This directly confirms that the cloned AvrL567 gene is responsible for flax rust virulence phenotypes, and demonstrates the utility of this system to probe rust gene function.

Jeffrey G Ellis - One of the best experts on this subject based on the ideXlab platform.

  • genome analysis and avirulence gene cloning using a high density radseq linkage map of the flax rust fungus Melampsora lini
    BMC Genomics, 2016
    Co-Authors: Claire Anderson, Gregory J. Lawrence, Adrienne R. Hardham, Adnane Nemri, Ann-maree Catanzariti, Muhammad Adil Khan, Cameron Jack, Narayana M Upadhyaya, Jeffrey G Ellis
    Abstract:

    Rust fungi are an important group of plant pathogens that cause devastating losses in agricultural, silvicultural and natural ecosystems. Plants can be protected from rust disease by resistance genes encoding receptors that trigger a highly effective defence response upon recognition of specific pathogen avirulence proteins. Identifying avirulence genes is crucial for understanding how virulence evolves in the field. To facilitate avirulence gene cloning in the flax rust fungus, Melampsora lini, we constructed a high-density genetic linkage map using single nucleotide polymorphisms detected in restriction site-associated DNA sequencing (RADseq) data. The map comprises 13,412 RADseq markers in 27 linkage groups that together span 5860 cM and contain 2756 recombination bins. The marker sequences were used to anchor 68.9 % of the M. lini genome assembly onto the genetic map. The map and anchored assembly were then used to: 1) show that M. lini has a high overall meiotic recombination rate, but recombination distribution is uneven and large coldspots exist; 2) show that substantial genome rearrangements have occurred in spontaneous loss-of-avirulence mutants; and 3) identify the AvrL2 and AvrM14 avirulence genes by map-based cloning. AvrM14 is a dual-specificity avirulence gene that encodes a predicted nudix hydrolase. AvrL2 is located in the region of the M. lini genome with the lowest recombination rate and encodes a small, highly-charged proline-rich protein. The M. lini high-density linkage map has greatly advanced our understanding of virulence mechanisms in this pathogen by providing novel insights into genome variability and enabling identification of two new avirulence genes.

  • the genome sequence and effector complement of the flax rust pathogen Melampsora lini
    Frontiers in Plant Science, 2014
    Co-Authors: Adnane Nemri, Gregory J. Lawrence, Claire Anderson, Narayana M Upadhyaya, Jeffrey G Ellis, Diane G O Saunders, Joe Win, David A Jones, Sophien Kamoun, Peter N. Dodds
    Abstract:

    Rust fungi cause serious yield reductions on crops, including wheat, barley, soybean, coffee, and represent real threats to global food security. Of these fungi, the flax rust pathogen Melampsora lini has been developed extensively over the past 80 years as a model to understand the molecular mechanisms that underpin pathogenesis. During infection, M. lini secretes virulence effectors to promote disease. The number of these effectors, their function and their degree of conservation across rust fungal species is unknown. To assess this, we sequenced and assembled de novo the genome of M. lini isolate CH5 into 21,130 scaffolds spanning 189 Mbp (scaffold N50 of 31 kbp). Global analysis of the DNA sequence revealed that repetitive elements, primarily retrotransposons, make up at least 45% of the genome. Using ab initio predictions, transcriptome data and homology searches, we identified 16,271 putative protein-coding genes. An analysis pipeline was then implemented to predict the effector complement of M. lini and compare it to that of the poplar rust, wheat stem rust and wheat stripe rust pathogens to identify conserved and species-specific effector candidates. Previous knowledge of four cloned M. lini avirulence effector proteins and two basidiomycete effectors was used to optimise parameters of the effector prediction pipeline. Markov clustering based on sequence similarity was performed to group effector candidates from all four rust pathogens. Clusters containing at least one member from M. lini were further analysed and prioritized based on features including expression in isolated haustoria and infected leaf tissue and conservation across rust species. Herein, we describe 200 of 940 clusters that ranked highest on our priority list, representing 725 flax rust candidate effectors. Our findings on this important model rust species provide insight into how effectors of rust fungi are conserved across species and how they may act to promote infection on their hosts.

  • Crystal Structures of Flax Rust Avirulence Proteins AvrL567-A and-D Reveal Details of the Structural Basis for Flax Disease Resistance Specificity W
    2013
    Co-Authors: Ching-i A. Wang, Ann-maree Catanzariti, Jeffrey G Ellis, Gregor Gunčar, Jade K. Forwood, Trazel Teh, Peter C N. Dodds
    Abstract:

    The gene-for-gene mechanism of plant disease resistance involves direct or indirect recognition of pathogen avirulence (Avr) proteins by plant resistance (R) proteins. Flax rust (Melampsora lini) AvrL567 avirulence proteins and the corresponding flax (Linum usitatissimum) L5, L6, and L7 resistance proteins interact directly. We determined the three-dimensional structures of two members of the AvrL567 family, AvrL567-A and AvrL567-D, at 1.4- and 2.3-A ˚ resolution, respectively. The structures of both proteins are very similar and reveal a b-sandwich fold with no close known structural homologs. The polymorphic residues in the AvrL567 family map to the surface of the protein, and polymorphisms in residues associated with recognition differences for the R proteins lead to significant changes in surface chemical properties. Analysis of single amino acid substitutions in AvrL567 proteins confirm the role of individual residues in conferring differences in recognition and suggest that the specificity results from the cumulative effects of multiple amino acid contacts. The structures also provide insights into possible pathogen-associated functions of AvrL567 proteins, with nucleic acid binding activity demonstrated in vitro. Our studie

  • structural and functional analysis of a plant resistance protein tir domain reveals interfaces for self association signaling and autoregulation
    Cell Host & Microbe, 2011
    Co-Authors: Maud Bernoux, Bostjan Kobe, Simon J. Williams, Xiaoxiao Zhang, Jeffrey G Ellis, Christopher Warren, Danny M Hatters, Eugene Valkov, Peter N. Dodds
    Abstract:

    The Toll/interleukin-1 receptor (TIR) domain occurs in animal and plant immune receptors. In the animal Toll-like receptors, homodimerization of the intracellular TIR domain is required for initiation of signaling cascades leading to innate immunity. By contrast, the role of the TIR domain in cytoplasmic nucleotide-binding/leucine-rich repeat (NB-LRR) plant immune resistance proteins is poorly understood. L6 is a TIR-NB-LRR resistance protein from flax (Linum usitatissimum) that confers resistance to the flax rust phytopathogenic fungus (Melampsora lini). We determine the crystal structure of the L6 TIR domain and show that, although dispensable for pathogenic effector protein recognition, the TIR domain alone is both necessary and sufficient for L6 immune signaling. We demonstrate that the L6 TIR domain self-associates, most likely forming a homodimer. Analysis of the structure combined with site-directed mutagenesis suggests that self-association is a requirement for immune signaling and reveals distinct surface regions involved in self-association, signaling, and autoregulation.

  • internalization of flax rust avirulence proteins into flax and tobacco cells can occur in the absence of the pathogen
    The Plant Cell, 2010
    Co-Authors: Maryam Rafiqi, Gregory J. Lawrence, Adrienne R. Hardham, Jeffrey G Ellis, David A Jones, Pamela H P Gan, Michael Ravensdale, Peter N. Dodds
    Abstract:

    Translocation of pathogen effector proteins into the host cell cytoplasm is a key determinant for the pathogenicity of many bacterial and oomycete plant pathogens. A number of secreted fungal avirulence (Avr) proteins are also inferred to be delivered into host cells, based on their intracellular recognition by host resistance proteins, including those of flax rust (Melampsora lini). Here, we show by immunolocalization that the flax rust AvrM protein is secreted from haustoria during infection and accumulates in the haustorial wall. Five days after inoculation, the AvrM protein was also detected within the cytoplasm of a proportion of plant cells containing haustoria, confirming its delivery into host cells during infection. Transient expression of secreted AvrL567 and AvrM proteins fused to cerulean fluorescent protein in tobacco (Nicotiana tabacum) and flax cells resulted in intracellular accumulation of the fusion proteins. The rust Avr protein signal peptides were functional in plants and efficiently directed fused cerulean into the secretory pathway. Thus, these secreted effectors are internalized into the plant cell cytosol in the absence of the pathogen, suggesting that they do not require a pathogen-encoded transport mechanism. Uptake of these proteins is dependent on signals in their N-terminal regions, but the primary sequence features of these uptake regions are not conserved between different rust effectors.

J J Burdon - One of the best experts on this subject based on the ideXlab platform.

  • genetic analysis reveals long standing population differentiation and high diversity in the rust pathogen Melampsora lini
    PLOS Pathogens, 2020
    Co-Authors: Hanna Susi, Peter H Thrall, J J Burdon, Adnane Nemri, Luke G Barrett
    Abstract:

    A priority for research on infectious disease is to understand how epidemiological and evolutionary processes interact to influence pathogen population dynamics and disease outcomes. However, little is understood about how population adaptation changes across time, how sexual vs. asexual reproduction contribute to the spread of pathogens in wild populations and how diversity measured with neutral and selectively important markers correlates across years. Here, we report results from a long-term study of epidemiological and genetic dynamics within several natural populations of the Linum marginale-Melampsora lini plant-pathogen interaction. Using pathogen isolates collected from three populations of wild flax (L. marginale) spanning 16 annual epidemics, we probe links between pathogen population dynamics, phenotypic variation for infectivity and genomic polymorphism. Pathogen genotyping was performed using 1567 genome-wide SNP loci and sequence data from two infectivity loci (AvrP123, AvrP4). Pathogen isolates were phenotyped for infectivity using a differential set. Patterns of epidemic development were assessed by conducting surveys of infection prevalence in one population (Kiandra) annually. Bayesian clustering analyses revealed host population and ecotype as key predictors of pathogen genetic structure. Despite strong fluctuations in pathogen population size and severe annual bottlenecks, analysis of molecular variance revealed that pathogen population differentiation was relatively stable over time. Annually, varying levels of clonal spread (0-44.8%) contributed to epidemics. However, within populations, temporal genetic composition was dynamic with rapid turnover of pathogen genotypes, despite the dominance of only four infectivity phenotypes across the entire study period. Furthermore, in the presence of strong fluctuations in population size and migration, spatial selection may maintain pathogen populations that, despite being phenotypically stable, are genetically highly dynamic.

  • local demographic and epidemiological patterns in the linum marginale Melampsora lini association a multi year study
    Journal of Ecology, 2017
    Co-Authors: Peter H Thrall, Hanna Susi, Luke G Barrett, J J Burdon
    Abstract:

    Summary 1.Many theoretical and empirical studies operate from an assumption that pathogens have a significant influence on the fecundity and lifespan of their host species. However, there is surprisingly little data investigating the long-term fitness impacts and genetic consequences that arise from pathogen infection in natural populations. Here, we address this gap through the analysis of a dataset investigating the local population dynamics of a native host plant (Linum marginale) and an associated rust pathogen (Melampsora lini) across 12 years. 2.To investigate patterns of disease prevalence and severity and track effects on host fecundity and demography we conducted censuses on an annual basis at a single site. Annual M. lini infection prevalence ranged from 0% to 99%. Severe epidemics occurred in 3-4 year cycles causing high overwintering mortality and subsequent changes in the relative abundance of different host phenotypes. Host population size oscillated in response to epidemics and declined towards the end of the observation period. Changes in host numbers were found to affect disease severity but not infection prevalence. 3.Melampsora lini infection increased L. marginale fecundity; the infected plants produced three fold more seed capsules on average than uninfected plants (13.3 vs 4.3 seed capsules per plant). 4.To investigate how variation in environmental conditions affects epidemiology and host demography, we identified climatic factors affecting host growth, overwintering, and disease severity. Winter (June) rainfall increased host overwintering success and summer (December) rainfall favoured host growth. The progress of Melampsora lini disease epidemics benefited from optimal temperatures in February and suffered from rainfall in January. 5.We further examined links between the genetic structure of the pathogen population and disease dynamics. There was a positive correlation between mean pathogen infectivity (as measured across a host differential set) and the severity of disease epidemics. 6.Synthesis. Our results provide new insights into local drivers and consequences of pathogen epidemiology in natural populations. Melampsora lini infection can have profound consequences on the phenotype, demography and population structure of Linum marginale by increasing host fecundity, overwinter mortality and disease resistance. This article is protected by copyright. All rights reserved.

  • below ground abiotic and biotic heterogeneity shapes above ground infection outcomes and spatial divergence in a host parasite interaction
    New Phytologist, 2015
    Co-Authors: Annaliisa Laine, J J Burdon, Ayco J M Tack, Andrew Bissett, Peter H Thrall
    Abstract:

    genotype9genotype9 environment (G 9G9 E), tradeoffs. Summary We investigated the impact of below-ground and above-ground environmental heterogeneity on the ecology and evolution of a natural plant–pathogen interaction. We combined field measurements and a reciprocal inoculation experiment to investigate the potential for natural variation in abiotic and biotic factors to mediate infection outcomes in the association between the fungal pathogen Melampsora lini and its wild flax host, Linum marginale, where pathogen strains and plant lines originated from two ecologically distinct habitat types that occur in close proximity (‘bog’ and ‘hill’). The two habitat types differed strikingly in soil moisture and soil microbiota. Infection outcomes for different host–pathogen combinations were strongly affected by the habitat of origin of the plant lines and pathogen strains, the soil environment and their interactions. Our results suggested that tradeoffs play a key role in explaining the evolutionary divergence in interaction traits among the two habitat types. Overall, we demonstrate that soil heterogeneity, by mediating infection outcomes and evolutionary divergence, can contribute to the maintenance of variation in resistance and pathogenicity within a natural host–pathogen metapopulation.

  • host ecotype generates evolutionary and epidemiological divergence across a pathogen metapopulation
    Proceedings of The Royal Society B: Biological Sciences, 2014
    Co-Authors: Annaliisa Laine, J J Burdon, Adnane Nemri, Peter H Thrall
    Abstract:

    The extent and speed at which pathogens adapt to host resistance varies considerably. This presents a challenge for predicting when—and where—pathogen evolution may occur. While gene flow and spatially heterogeneous environments are recognized to be critical for the evolutionary potential of pathogen populations, we lack an understanding of how the two jointly shape coevolutionary trajectories between hosts and pathogens. The rust pathogen Melampsora lini infects two ecotypes of its host plant Linum marginale that occur in close proximity yet in distinct populations and habitats. In this study, we found that within-population epidemics were different between the two habitats. We then tested for pathogen local adaptation at host population and ecotype level in a reciprocal inoculation study. Even after controlling for the effect of spatial structure on infection outcome, we found strong evidence of pathogen adaptation at the host ecotype level. Moreover, sequence analysis of two pathogen infectivity loci revealed strong genetic differentiation by host ecotype but not by distance. Hence, environmental variation can be a key determinant of pathogen population genetic structure and coevolutionary dynamics and can generate strong asymmetry in infection risks through space.

  • population processes at multiple spatial scales maintain diversity and adaptation in the linum marginale Melampsora lini association
    PLOS ONE, 2012
    Co-Authors: Adnane Nemri, Annaliisa Laine, J J Burdon, Luke G Barrett, Peter H Thrall
    Abstract:

    Host-pathogen coevolution is a major driver of species diversity, with an essential role in the generation and maintenance of genetic variation in host resistance and pathogen infectivity. Little is known about how resistance and infectivity are structured across multiple geographic scales and what eco-evolutionary processes drive these patterns. Across southern Australia, the wild flax Linum marginale is frequently attacked by its rust fungus Melampsora lini. Here, we compare the genetic and phenotypic structure of resistance and infectivity among population pairs from two regions where environmental differences associate with specific life histories and mating systems. We find that both host and pathogen populations are genetically distinct between these regions. The region with outcrossing hosts and pathogens that go through asexual cycles followed by sexual reproduction showed greater diversity of resistance and infectivity phenotypes, higher levels of resistance and less clumped within-population spatial distribution of resistance. However, in the region where asexual pathogens infect selfing hosts, pathogens were more infective and better adapted to sympatric hosts. Our findings largely agree with expectations based on the distinctly different host mating systems in the two regions, with a likely advantage for hosts undergoing recombination. For the pathogen in this system, sexual reproduction may primarily be a survival mechanism in the region where it is observed. While it appears to potentially have adverse effects on local adaptation in the short term, it may be necessary for longer-term coevolution with outcrossing hosts.

Peter H Thrall - One of the best experts on this subject based on the ideXlab platform.

  • genetic analysis reveals long standing population differentiation and high diversity in the rust pathogen Melampsora lini
    PLOS Pathogens, 2020
    Co-Authors: Hanna Susi, Peter H Thrall, J J Burdon, Adnane Nemri, Luke G Barrett
    Abstract:

    A priority for research on infectious disease is to understand how epidemiological and evolutionary processes interact to influence pathogen population dynamics and disease outcomes. However, little is understood about how population adaptation changes across time, how sexual vs. asexual reproduction contribute to the spread of pathogens in wild populations and how diversity measured with neutral and selectively important markers correlates across years. Here, we report results from a long-term study of epidemiological and genetic dynamics within several natural populations of the Linum marginale-Melampsora lini plant-pathogen interaction. Using pathogen isolates collected from three populations of wild flax (L. marginale) spanning 16 annual epidemics, we probe links between pathogen population dynamics, phenotypic variation for infectivity and genomic polymorphism. Pathogen genotyping was performed using 1567 genome-wide SNP loci and sequence data from two infectivity loci (AvrP123, AvrP4). Pathogen isolates were phenotyped for infectivity using a differential set. Patterns of epidemic development were assessed by conducting surveys of infection prevalence in one population (Kiandra) annually. Bayesian clustering analyses revealed host population and ecotype as key predictors of pathogen genetic structure. Despite strong fluctuations in pathogen population size and severe annual bottlenecks, analysis of molecular variance revealed that pathogen population differentiation was relatively stable over time. Annually, varying levels of clonal spread (0-44.8%) contributed to epidemics. However, within populations, temporal genetic composition was dynamic with rapid turnover of pathogen genotypes, despite the dominance of only four infectivity phenotypes across the entire study period. Furthermore, in the presence of strong fluctuations in population size and migration, spatial selection may maintain pathogen populations that, despite being phenotypically stable, are genetically highly dynamic.

  • local demographic and epidemiological patterns in the linum marginale Melampsora lini association a multi year study
    Journal of Ecology, 2017
    Co-Authors: Peter H Thrall, Hanna Susi, Luke G Barrett, J J Burdon
    Abstract:

    Summary 1.Many theoretical and empirical studies operate from an assumption that pathogens have a significant influence on the fecundity and lifespan of their host species. However, there is surprisingly little data investigating the long-term fitness impacts and genetic consequences that arise from pathogen infection in natural populations. Here, we address this gap through the analysis of a dataset investigating the local population dynamics of a native host plant (Linum marginale) and an associated rust pathogen (Melampsora lini) across 12 years. 2.To investigate patterns of disease prevalence and severity and track effects on host fecundity and demography we conducted censuses on an annual basis at a single site. Annual M. lini infection prevalence ranged from 0% to 99%. Severe epidemics occurred in 3-4 year cycles causing high overwintering mortality and subsequent changes in the relative abundance of different host phenotypes. Host population size oscillated in response to epidemics and declined towards the end of the observation period. Changes in host numbers were found to affect disease severity but not infection prevalence. 3.Melampsora lini infection increased L. marginale fecundity; the infected plants produced three fold more seed capsules on average than uninfected plants (13.3 vs 4.3 seed capsules per plant). 4.To investigate how variation in environmental conditions affects epidemiology and host demography, we identified climatic factors affecting host growth, overwintering, and disease severity. Winter (June) rainfall increased host overwintering success and summer (December) rainfall favoured host growth. The progress of Melampsora lini disease epidemics benefited from optimal temperatures in February and suffered from rainfall in January. 5.We further examined links between the genetic structure of the pathogen population and disease dynamics. There was a positive correlation between mean pathogen infectivity (as measured across a host differential set) and the severity of disease epidemics. 6.Synthesis. Our results provide new insights into local drivers and consequences of pathogen epidemiology in natural populations. Melampsora lini infection can have profound consequences on the phenotype, demography and population structure of Linum marginale by increasing host fecundity, overwinter mortality and disease resistance. This article is protected by copyright. All rights reserved.

  • Population Processes at Multiple Spatial Scales Maintain Diversity and Adaptation in the Linum marginale- Melampsora lini Association
    2016
    Co-Authors: Marginale Melampsora Lini Association, Jeremy J. Burdon, Peter H Thrall, Annaliisa Laine, Adnane Nemri, Luke G Barrett, Jeremy Burdon
    Abstract:

    Host-pathogen coevolution is a major driver of species diversity, with an essential role in the generation and maintenance of genetic variation in host resistance and pathogen infectivity. Little is known about how resistance and infectivity are structured across multiple geographic scales and what eco-evolutionary processes drive these patterns. Across southern Australia, the wild flax Linum marginale is frequently attacked by its rust fungus Melampsora lini. Here, we compare the genetic and phenotypic structure of resistance and infectivity among population pairs from two regions where environmental differences associate with specific life histories and mating systems. We find that both host and pathogen populations are genetically distinct between these regions. The region with outcrossing hosts and pathogens that go through asexual cycles followed by sexual reproduction showed greater diversity of resistance and infectivity phenotypes, higher levels of resistance and less clumped within-population spatial distribution of resistance. However, in the region where asexual pathogens infect selfing hosts, pathogens were more infective and better adapted to sympatric hosts. Ou

  • below ground abiotic and biotic heterogeneity shapes above ground infection outcomes and spatial divergence in a host parasite interaction
    New Phytologist, 2015
    Co-Authors: Annaliisa Laine, J J Burdon, Ayco J M Tack, Andrew Bissett, Peter H Thrall
    Abstract:

    genotype9genotype9 environment (G 9G9 E), tradeoffs. Summary We investigated the impact of below-ground and above-ground environmental heterogeneity on the ecology and evolution of a natural plant–pathogen interaction. We combined field measurements and a reciprocal inoculation experiment to investigate the potential for natural variation in abiotic and biotic factors to mediate infection outcomes in the association between the fungal pathogen Melampsora lini and its wild flax host, Linum marginale, where pathogen strains and plant lines originated from two ecologically distinct habitat types that occur in close proximity (‘bog’ and ‘hill’). The two habitat types differed strikingly in soil moisture and soil microbiota. Infection outcomes for different host–pathogen combinations were strongly affected by the habitat of origin of the plant lines and pathogen strains, the soil environment and their interactions. Our results suggested that tradeoffs play a key role in explaining the evolutionary divergence in interaction traits among the two habitat types. Overall, we demonstrate that soil heterogeneity, by mediating infection outcomes and evolutionary divergence, can contribute to the maintenance of variation in resistance and pathogenicity within a natural host–pathogen metapopulation.

  • host ecotype generates evolutionary and epidemiological divergence across a pathogen metapopulation
    Proceedings of The Royal Society B: Biological Sciences, 2014
    Co-Authors: Annaliisa Laine, J J Burdon, Adnane Nemri, Peter H Thrall
    Abstract:

    The extent and speed at which pathogens adapt to host resistance varies considerably. This presents a challenge for predicting when—and where—pathogen evolution may occur. While gene flow and spatially heterogeneous environments are recognized to be critical for the evolutionary potential of pathogen populations, we lack an understanding of how the two jointly shape coevolutionary trajectories between hosts and pathogens. The rust pathogen Melampsora lini infects two ecotypes of its host plant Linum marginale that occur in close proximity yet in distinct populations and habitats. In this study, we found that within-population epidemics were different between the two habitats. We then tested for pathogen local adaptation at host population and ecotype level in a reciprocal inoculation study. Even after controlling for the effect of spatial structure on infection outcome, we found strong evidence of pathogen adaptation at the host ecotype level. Moreover, sequence analysis of two pathogen infectivity loci revealed strong genetic differentiation by host ecotype but not by distance. Hence, environmental variation can be a key determinant of pathogen population genetic structure and coevolutionary dynamics and can generate strong asymmetry in infection risks through space.