Publications by authors named "Ioannis Stergiopoulos"

39 Publications

Repeated exposure of spores to the antifungal bacterium Ter331 selects for delayed spore germination.

Appl Environ Microbiol 2021 Apr 2. Epub 2021 Apr 2.

Department of Plant Pathology, University of California Davis, Davis, California, USA.

The bacterial strain Ter331 (CfTer331) inhibits mycelial growth and spore germination in N402 (AnN402). The mechanisms underlying this antagonistic bacterial-fungal interaction have been extensively studied, but knowledge on the long-term outcome of this interaction is currently lacking. Here, we used experimental evolution to explore the dynamics of fungal adaptation to recurrent exposure to CfTer331. Specifically, five single-spore isolates (SSIs) of AnN402 were evolved under three selection scenarios in liquid culture, i.e. (i) in the presence of CfTer331 for 80 growth cycles, (ii) in the absence of the bacterium for 80 cycles, and (iii) in the presence of CfTer331 for 40 cycles and then another 40 cycles in its absence. The evolved SSI lineages were then evaluated for phenotypic changes from the founder fungal strain, such as germinability with or without CfTer331. The analysis showed that recurrent exposure to CfTer331 selected for fungal lineages with reduced germinability and slower germination, even in the absence of CfTer331. In contrast, when AnN402 evolved in the absence of the bacteria, then lineages with increased germinability and faster germination were favored. SSIs that were first evolved in the presence of CfTer331 and then in its absence, showed intermediate phenotypes but overall were more similar to SSIs that evolved in the absence of CfTer331 for 80 cycles. This suggests that traits acquired from exposure to CfTer331 were reversible upon removal of the selection pressure. Overall, our study provides insights into the effects on fungi from the long-term co-culture with bacteria.The use of antagonistic bacteria for managing fungal diseases is becoming increasingly popular, and thus there is a need to understand the implications of their long-term use against fungi. Most efforts have so far focused on characterizing the antifungal properties and mode of action of the bacterial antagonists, but the possible outcomes of the persisting interaction between antagonistic bacteria and fungi are not well understood. In this study, we used experimental evolution in order to explore the evolutionary aspects of an antagonistic bacterial-fungal interaction, using the antifungal bacterium and the fungus as a model system. We show that evolution in the presence or absence of the bacteria selects for fungal lineages with opposing and conditionally beneficial traits such as slow and fast spore germination, respectively. Overall, our studies reveal that fungal responses to biotic factors related to antagonism could be to some extent predictable and reversible.
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http://dx.doi.org/10.1128/AEM.00233-21DOI Listing
April 2021

A world-wide analysis of reduced sensitivity to DMI fungicides in the banana pathogen Pseudocercospora fijiensis.

Pest Manag Sci 2021 Mar 25. Epub 2021 Mar 25.

Wageningen Research, Wageningen University and Research, Wageningen, The Netherlands.

Background: Pseudocercospora fijiensis is the causal agent of the black leaf streak disease (BLSD) of banana. Bananas are important global export commodities and a major staple food. Their susceptibility to BLSD pushes disease management towards excessive fungicide use, largely relying on multisite inhibitors and sterol demethylation inhibitors (DMIs). These fungicides are ubiquitous in plant disease control, targeting the CYP51 enzyme. We examined sensitivity to DMIs in P. fijiensis field isolates collected from various major banana production zones in Colombia, Costa Rica, Dominican Republic, Ecuador, the Philippines, Guadalupe, Martinique and Cameroon and determined the underlying genetic reasons for the observed phenotypes.

Results: We observed a continuous range of sensitivity towards the DMI fungicides difenoconazole, epoxiconazole and propiconazole with clear cross-sensitivity. Sequence analyses of PfCYP51 in 266 isolates showed 28 independent amino acid substitutions, nine of which correlated with reduced sensitivity to DMIs. In addition to the mutations, we observed up to six insertions in the Pfcyp51 promoter. Such promoter insertions contain repeated elements with a palindromic core and correlate with the enhanced expression of Pfcyp51 and hence with reduced DMI sensitivity. Wild-type isolates from unsprayed bananas fields did not contain any promoter insertions.

Conclusion: The presented data significantly contribute to understanding of the evolution and global distribution of DMI resistance mechanisms in P. fijiensis field populations and facilitate the prediction of different DMI efficacy. The overall reduced DMI sensitivity calls for the deployment of a wider range of solutions for sustainable control of this major banana disease.
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http://dx.doi.org/10.1002/ps.6372DOI Listing
March 2021

Targeted Delivery of Gene Silencing in Fungi Using Genetically Engineered Bacteria.

J Fungi (Basel) 2021 Feb 9;7(2). Epub 2021 Feb 9.

Department of Plant Pathology, University of California Davis, Davis, CA 95616, USA.

Exploiting RNA interference (RNAi) in disease control through non-transformative methods that overcome the hurdle of producing transgenic plants has attracted much attention over the last years. Here, we explored such a method and used non-pathogenic bacteria as a versatile system for delivering RNAi to fungi. Specifically, the RNaseIII-null mutant strain of HT115(DE3) was transformed with two plasmid vectors that enabled the constitutive or IPTG-inducible production of double-stranded RNAs (dsRNAs) against genes involved in aflatoxins production in () or virulence of (). To facilitate the release of the dsRNAs, the bacterial cells were further genetically engineered to undergo a bacteriophage endolysin R-mediated autolysis, following a freeze-thaw cycle. Exposure under in vitro conditions of or to living bacteria or their whole-cell autolysates induced silencing of and in a bacteria concentration-dependent manner, and instigated a reduction in aflatoxins production and mycelial growth, respectively. In planta applications of the living bacteria or their crude whole-cell autolysates produced similar results, thus creating a basis for translational research. These results demonstrate that bacteria can produce biologically active dsRNA against target genes in fungi and that bacteria-mediated RNAi can be used to control fungal pathogens.
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http://dx.doi.org/10.3390/jof7020125DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC7914413PMC
February 2021

Allele-Specific Detection Methods for QoI Fungicide-Resistant in Vineyards.

Plant Dis 2021 Jan 13;105(1):175-182. Epub 2020 Nov 13.

United States Department of Agriculture-Agricultural Research Service, Corvallis, OR 97330.

Grapevine powdery mildew (GPM), caused by the fungus , is a constant threat to worldwide production of grape berries, requiring repeated use of fungicides for management. The frequent fungicide applications have resulted in resistance to commonly used quinone outside inhibitor (QoI) fungicides and the resistance is associated with single-nucleotide polymorphisms (SNPs) in the mitochondrial gene (). In this study, we attempted to detect the most common SNP causing a glycine to alanine substitution at amino acid position 143 (i.e., G143A) in the protein, to track this resistance using allele-specific TaqMan probe and digital-droplet PCR-based assays. Specificity and sensitivity of these assays showed that these two assays could discriminate SNPs and were effective on mixed samples. These diagnostic assays were implemented to survey samples collected from leaf and air samples from California and Oregon grape-growing regions. Sequencing of PCR amplicons and phenotyping of isolates also revealed that these assays accurately detected each allele (100% agreement), and there was an absolute agreement between the presence or absence of the G143A mutation and resistance to QoIs in the sampled. These results indicate that the developed diagnostic tools will help growers make informed decisions about fungicide selections and applications which, in turn, will facilitate GPM disease management and improve grape production systems.
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http://dx.doi.org/10.1094/PDIS-11-19-2395-REDOI Listing
January 2021

First Draft Genome Resource for the Tomato Black Leaf Mold Pathogen .

Mol Plant Microbe Interact 2020 Dec 12;33(12):1441-1445. Epub 2020 Oct 12.

Department of Plant Pathology, University of California Davis, One Shields Avenue, Davis, CA 95616-8751, U.S.A.

is a fungus that causes black leaf mold, an important disease of tomato in tropical and subtropical regions of the world. Despite its economic importance, genomic resources for this pathogen are scarce and no reference genome was available thus far. Here, we report a 50.6-Mb genome assembly for consisting of 348 contigs with an N value of 0.407 Mb. In total, 13,764 protein-coding genes were predicted with an estimated BUSCO completeness of 98%. Among the predicted genes there were 179 candidate effectors, 445 carbohydrate-active enzymes, and 30 secondary metabolite gene clusters. The resources presented in this study will allow genome-wide comparative analyses and population genomic studies of this pathogen, ultimately improving management strategies for black leaf mold of tomato.
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http://dx.doi.org/10.1094/MPMI-06-20-0139-ADOI Listing
December 2020

Interruption of Aspergillus niger spore germination by the bacterially produced secondary metabolite collimomycin.

Environ Microbiol Rep 2020 06 21;12(3):306-313. Epub 2020 Mar 21.

Department of Plant Pathology, University of California Davis, One Shields Avenue, Davis, CA, 95616-8751.

Collimonas fungivorans Ter331 (CfTer331) is a soil bacterium that produces collimomycin, a secondary metabolite that inhibits the vegetative growth of fungi. Here we show that CfTer331 can also interfere with fungal spore germination and that collimomycin biosynthesis is required for this activity. More specifically, in co-cultures of Aspergillus niger N402 (AnN402) co-nidiospores with CfTer331, the rate of transition from the isotropic to polarized stage of the germination process was reduced and the relatively few AnN402 conidiospores that completed the germination process were less likely to survive than those that were arrested in the isotropic phase. By contrast, a collimomycin-deficient mutant of CfTer331 had no effect on germination: in its presence, as in the absence or delayed presence of CfTer331, unhindered germination of conidiospores allowed rapid establishment of AnN402 mycelium and the subsequent acidification of the culture medium to the detriment of any bacteria present. However, when challenged early enough with CfTer331, the collimomycin-dependent arrest of the AnN402 germination process enabled CfTer331 to prevent AnN402 from forming mycelia and to gain dominance in the culture. We propose that the collimomycin-dependent arrest of spore germination represents an early intervention strategy used by CfTer331 to mitigate niche construction by fungi in nature.
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http://dx.doi.org/10.1111/1758-2229.12833DOI Listing
June 2020

Cloning of the Cytochrome Gene From the Tomato Powdery Mildew Fungus Reveals High Levels of Allelic Variation and Heteroplasmy for the G143A Mutation.

Front Microbiol 2019 10;10:663. Epub 2019 Apr 10.

Department of Plant Pathology, University of California, Davis, Davis, CA, United States.

is a major pathogen of tomato and several other crops that can cause substantial yield losses in favorable conditions for the fungus. Quinone outside inhibitor fungicides (QIs) are routinely used for the control of the pathogen in tomato fields across California, but their recurrent use could lead to the emergence of resistance against these compounds. Here, we partially cloned the cytochrome gene from () and searched within populations of the fungus collected from tomato fields across California for mutations that confer resistance to QIs. A total of 21 single nucleotide polymorphisms (SNPs) were identified within a 704 bp fragment of the gene analyzed, of which five were non-synonymous substitutions. Among the most frequent SNPs encountered within field populations of the pathogen was the G143A substitution that confers high levels of resistance against QIs in several fungi. The other four amino acid substitutions were novel mutations, whose effect on QI resistance is currently unknown. Sequencing of the gene from individual single-cell conidia of the fungus further revealed that most SNPs, including the one leading to the G143A substitution, were present in a heteroplasmic state, indicating the co-existence of multiple mitotypes in single cells. Analysis of the field samples showed that the G143A substitution is predominantly heteroplasmic also within field populations of in California, suggesting that QI resistance in this fungus is likely to be quantitative rather than qualitative.
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http://dx.doi.org/10.3389/fmicb.2019.00663DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6467933PMC
April 2019

Structure of the Cladosporium fulvum Avr4 effector in complex with (GlcNAc)6 reveals the ligand-binding mechanism and uncouples its intrinsic function from recognition by the Cf-4 resistance protein.

PLoS Pathog 2018 08 27;14(8):e1007263. Epub 2018 Aug 27.

Department of Chemistry, University of California, Davis, Davis, California, United States of America.

Effectors are microbial-derived secreted proteins with an essential function in modulating host immunity during infections. CfAvr4, an effector protein from the tomato pathogen Cladosporium fulvum and the founding member of a fungal effector family, promotes parasitism through binding fungal chitin and protecting it from chitinases. Binding of Avr4 to chitin is mediated by a carbohydrate-binding module of family 14 (CBM14), an abundant CBM across all domains of life. To date, the structural basis of chitin-binding by Avr4 effector proteins and of recognition by the cognate Cf-4 plant immune receptor are still poorly understood. Using X-ray crystallography, we solved the crystal structure of CfAvr4 in complex with chitohexaose [(GlcNAc)6] at 1.95Å resolution. This is the first co-crystal structure of a CBM14 protein together with its ligand that further reveals the molecular mechanism of (GlcNAc)6 binding by Avr4 effector proteins and CBM14 family members in general. The structure showed that two molecules of CfAvr4 interact through the ligand and form a three-dimensional molecular sandwich that encapsulates two (GlcNAc)6 molecules within the dimeric assembly. Contrary to previous assumptions made with other CBM14 members, the chitohexaose-binding domain (ChBD) extends to the entire length of CfAvr4 with the reducing end of (GlcNAc)6 positioned near the N-terminus and the non-reducing end at the C-terminus. Site-directed mutagenesis of residues interacting with (GlcNAc)6 enabled the elucidation of the precise topography and amino acid composition of Avr4's ChBD and further showed that these residues do not individually mediate the recognition of CfAvr4 by the Cf-4 immune receptor. Instead, the studies highlighted the dependency of Cf-4-mediated recognition on CfAvr4's stability and resistance against proteolysis in the leaf apoplast, and provided the evidence for structurally separating intrinsic function from immune receptor recognition in this effector family.
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http://dx.doi.org/10.1371/journal.ppat.1007263DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6128652PMC
August 2018

Silencing of the Mitogen-Activated Protein Kinases (MAPK) and in Reduces Growth and Virulence on Host Plants.

Front Plant Sci 2018 13;9:291. Epub 2018 Mar 13.

International Institute of Tropical Agriculture, Nairobi, Kenya.

, causal agent of the black Sigatoka disease (BSD) of spp., has spread globally since its discovery in Fiji 1963 all the banana and plantain growing areas across the globe. It is becoming the most damaging and economically important disease of this crop. The identification and characterization of genes that regulate infection processes and pathogenicity in will provide important knowledge for the development of disease-resistant cultivars. In many fungal plant pathogens, the and are reported to be essential for pathogenicity. regulates filamentous-invasion pathways including the formation of infection structures, sporulation, virulence, and invasive and filamentous growth, whereas is involved in the cell-wall integrity pathway, virulence, invasive growth, and colonization in host tissues. Here, we used RNAi-mediated gene silencing to investigate the role of the and homologs in in pathogen invasiveness, growth and pathogenicity. The and silenced transformants showed significantly lower gene expression and reduced virulence, invasive growth, and lower biomass in infected leaf tissues of East African Highland Banana (EAHB). This study suggests that and MAPK signaling pathways play important roles in plant infection and pathogenic growth of fungal pathogens. The silencing of these vital fungal genes through host-induced gene silencing (HIG) could be an alternative strategy for developing transgenic banana and plantain resistant to BSD.
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http://dx.doi.org/10.3389/fpls.2018.00291DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5859377PMC
March 2018

A new mechanism for reduced sensitivity to demethylation-inhibitor fungicides in the fungal banana black Sigatoka pathogen Pseudocercospora fijiensis.

Mol Plant Pathol 2018 06 13;19(6):1491-1503. Epub 2018 Feb 13.

Wageningen University and Research, Wageningen Plant Research, 6700 AA Wageningen, the Netherlands.

The Dothideomycete Pseudocercospora fijiensis, previously Mycosphaerella fijiensis, is the causal agent of black Sigatoka, one of the most destructive diseases of bananas and plantains. Disease management depends on fungicide applications, with a major contribution from sterol demethylation-inhibitors (DMIs). The continued use of DMIs places considerable selection pressure on natural P. fijiensis populations, enabling the selection of novel genotypes with reduced sensitivity. The hitherto explanatory mechanism for this reduced sensitivity was the presence of non-synonymous point mutations in the target gene Pfcyp51, encoding the sterol 14α-demethylase enzyme. Here, we demonstrate a second mechanism involved in DMI sensitivity of P. fijiensis. We identified a 19-bp element in the wild-type (wt) Pfcyp51 promoter that concatenates in strains with reduced DMI sensitivity. A polymerase chain reaction (PCR) assay identified up to six Pfcyp51 promoter repeats in four field populations of P. fijiensis in Costa Rica. We used transformation experiments to swap the wt promoter of a sensitive field isolate with a promoter from a strain with reduced DMI sensitivity that comprised multiple insertions. Comparative in vivo phenotyping showed a functional and proportional up-regulation of Pfcyp51, which consequently decreased DMI sensitivity. Our data demonstrate that point mutations in the Pfcyp51 coding domain, as well as promoter inserts, contribute to the reduced DMI sensitivity of P. fijiensis. These results provide new insights into the importance of the appropriate use of DMIs and the need for the discovery of new molecules for black Sigatoka management.
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http://dx.doi.org/10.1111/mpp.12637DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6637983PMC
June 2018

-Mediated Transformation of to Determine the Role of in Osmotic Stress Regulation and Virulence Modulation.

Front Microbiol 2017 16;8:830. Epub 2017 May 16.

International Institute of Tropical AgricultureNairobi, Kenya.

Black Sigatoka disease, caused by is a serious constraint to banana production worldwide. The disease continues to spread in new ecological niches and there is an urgent need to develop strategies for its control. The high osmolarity glycerol (HOG) pathway in is well known to respond to changes in external osmolarity. HOG pathway activation leads to phosphorylation, activation and nuclear transduction of the HOG1 mitogen-activated protein kinases (MAPKs). The activated HOG1 triggers several responses to osmotic stress, including up or down regulation of different genes, regulation of protein translation, adjustments to cell cycle progression and synthesis of osmolyte glycerol. This study investigated the role of the MAPK-encoding gene on osmotic stress adaptation and virulence of nsis. RNA interference-mediated gene silencing of significantly suppressed growth of on potato dextrose agar media supplemented with 1 M NaCl, indicating that regulates osmotic stress. In addition, virulence of the -silenced mutants of on banana was significantly reduced, as observed from the low rates of necrosis and disease development on the infected leaves. Staining with lacto phenol cotton blue further confirmed the impaired mycelial growth of the in the infected leaf tissues, which was further confirmed with quantification of the fungal biomass using absolute- quantitative PCR. Collectively, these findings demonstrate that plays a critical role in osmotic stress regulation and virulence of on its host banana. Thus, could be an interesting target for the control of black Sigatoka disease in banana.
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http://dx.doi.org/10.3389/fmicb.2017.00830DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5432539PMC
May 2017

Comparative Genomics of the Sigatoka Disease Complex on Banana Suggests a Link between Parallel Evolutionary Changes in Pseudocercospora fijiensis and Pseudocercospora eumusae and Increased Virulence on the Banana Host.

PLoS Genet 2016 08 11;12(8):e1005904. Epub 2016 Aug 11.

Department of Plant Pathology, University of California Davis, Davis, California, United States of America.

The Sigatoka disease complex, caused by the closely-related Dothideomycete fungi Pseudocercospora musae (yellow sigatoka), Pseudocercospora eumusae (eumusae leaf spot), and Pseudocercospora fijiensis (black sigatoka), is currently the most devastating disease on banana worldwide. The three species emerged on bananas from a recent common ancestor and show clear differences in virulence, with P. eumusae and P. fijiensis considered the most aggressive. In order to understand the genomic modifications associated with shifts in the species virulence spectra after speciation, and to identify their pathogenic core that can be exploited in disease management programs, we have sequenced and analyzed the genomes of P. eumusae and P. musae and compared them with the available genome sequence of P. fijiensis. Comparative analysis of genome architectures revealed significant differences in genome size, mainly due to different rates of LTR retrotransposon proliferation. Still, gene counts remained relatively equal and in the range of other Dothideomycetes. Phylogenetic reconstruction based on a set of 46 conserved single-copy genes strongly supported an earlier evolutionary radiation of P. fijiensis from P. musae and P. eumusae. However, pairwise analyses of gene content indicated that the more virulent P. eumusae and P. fijiensis share complementary patterns of expansions and contractions in core gene families related to metabolism and enzymatic degradation of plant cell walls, suggesting that the evolution of virulence in these two pathogens has, to some extent, been facilitated by convergent changes in metabolic pathways associated with nutrient acquisition and assimilation. In spite of their common ancestry and shared host-specificity, the three species retain fairly dissimilar repertoires of effector proteins, suggesting that they likely evolved different strategies for manipulating the host immune system. Finally, 234 gene families, including seven putative effectors, were exclusively present in the three Sigatoka species, and could thus be related to adaptation to the banana host.
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http://dx.doi.org/10.1371/journal.pgen.1005904DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4981473PMC
August 2016

Combating a Global Threat to a Clonal Crop: Banana Black Sigatoka Pathogen Pseudocercospora fijiensis (Synonym Mycosphaerella fijiensis) Genomes Reveal Clues for Disease Control.

PLoS Genet 2016 08 11;12(8):e1005876. Epub 2016 Aug 11.

Plant Research International, Wageningen University and Research, Wageningen, The Netherlands.

Black Sigatoka or black leaf streak disease, caused by the Dothideomycete fungus Pseudocercospora fijiensis (previously: Mycosphaerella fijiensis), is the most significant foliar disease of banana worldwide. Due to the lack of effective host resistance, management of this disease requires frequent fungicide applications, which greatly increase the economic and environmental costs to produce banana. Weekly applications in most banana plantations lead to rapid evolution of fungicide-resistant strains within populations causing disease-control failures throughout the world. Given its extremely high economic importance, two strains of P. fijiensis were sequenced and assembled with the aid of a new genetic linkage map. The 74-Mb genome of P. fijiensis is massively expanded by LTR retrotransposons, making it the largest genome within the Dothideomycetes. Melting-curve assays suggest that the genomes of two closely related members of the Sigatoka disease complex, P. eumusae and P. musae, also are expanded. Electrophoretic karyotyping and analyses of molecular markers in P. fijiensis field populations showed chromosome-length polymorphisms and high genetic diversity. Genetic differentiation was also detected using neutral markers, suggesting strong selection with limited gene flow at the studied geographic scale. Frequencies of fungicide resistance in fungicide-treated plantations were much higher than those in untreated wild-type P. fijiensis populations. A homologue of the Cladosporium fulvum Avr4 effector, PfAvr4, was identified in the P. fijiensis genome. Infiltration of the purified PfAVR4 protein into leaves of the resistant banana variety Calcutta 4 resulted in a hypersensitive-like response. This result suggests that Calcutta 4 could carry an unknown resistance gene recognizing PfAVR4. Besides adding to our understanding of the overall Dothideomycete genome structures, the P. fijiensis genome will aid in developing fungicide treatment schedules to combat this pathogen and in improving the efficiency of banana breeding programs.
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http://dx.doi.org/10.1371/journal.pgen.1005876DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4981457PMC
August 2016

Structural Analysis of an Avr4 Effector Ortholog Offers Insight into Chitin Binding and Recognition by the Cf-4 Receptor.

Plant Cell 2016 08 8;28(8):1945-65. Epub 2016 Jul 8.

Department of Plant Pathology, University of California Davis, Davis, California 95616

Chitin is a key component of fungal cell walls and a potent inducer of innate immune responses. Consequently, fungi may secrete chitin-binding lectins, such as the Cf-Avr4 effector protein from the tomato pathogen Cladosporium fulvum, to shield chitin from host-derived chitinases during infection. Homologs of Cf-Avr4 are found throughout Dothideomycetes, and despite their modest primary sequence identity, many are perceived by the cognate tomato immune receptor Cf-4. Here, we determined the x-ray crystal structure of Pf-Avr4 from the tomato pathogen Pseudocercospora fuligena, thus providing a three-dimensional model of an Avr4 effector protein. In addition, we explored structural, biochemical, and functional aspects of Pf-Avr4 and Cf-Avr4 to further define the biology of core effector proteins and outline a conceptual framework for their pleiotropic recognition by single immune receptors. We show that Cf-Avr4 and Pf-Avr4 share functional specificity in binding (GlcNAc)6 and in providing protection against plant- and microbial-derived chitinases, suggesting a broader role beyond deregulation of host immunity. Furthermore, structure-guided site-directed mutagenesis indicated that residues in Pf-Avr4 important for binding chitin do not directly influence recognition by Cf-4 and further suggested that the property of recognition is structurally separated or does not fully overlap with the virulence function of the effector.
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http://dx.doi.org/10.1105/tpc.15.00893DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5006696PMC
August 2016

Plant-Pathogen Effectors: Cellular Probes Interfering with Plant Defenses in Spatial and Temporal Manners.

Annu Rev Phytopathol 2016 08 17;54:419-41. Epub 2016 Jan 17.

Department of Plant Pathology, University of California, Davis, California; email: , ,

Plants possess large arsenals of immune receptors capable of recognizing all pathogen classes. To cause disease, pathogenic organisms must be able to overcome physical barriers, suppress or evade immune perception, and derive nutrients from host tissues. Consequently, to facilitate some of these processes, pathogens secrete effector proteins that promote colonization. This review covers recent advances in the field of effector biology, focusing on conserved cellular processes targeted by effectors from diverse pathogens. The ability of effectors to facilitate pathogen entry into the host interior, suppress plant immune perception, and alter host physiology for pathogen benefit is discussed. Pathogens also deploy effectors in a spatial and temporal manner, depending on infection stage. Recent advances have also enhanced our understanding of effectors acting in specific plant organs and tissues. Effectors are excellent cellular probes that facilitate insight into biological processes as well as key points of vulnerability in plant immune signaling networks.
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http://dx.doi.org/10.1146/annurev-phyto-080615-100204DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC5283857PMC
August 2016

FPLC and liquid-chromatography mass spectrometry identify candidate necrosis-inducing proteins from culture filtrates of the fungal wheat pathogen Zymoseptoria tritici.

Fungal Genet Biol 2015 Jun;79:54-62

Wageningen University & Research Center, Plant Research International, 6708 PB Wageningen, The Netherlands. Electronic address:

Culture filtrates (CFs) of the fungal wheat pathogen Zymoseptoria tritici were assayed for necrosis-inducing activity after infiltration in leaves of various wheat cultivars. Active fractions were partially purified and characterized. The necrosis-inducing factors in CFs are proteinaceous, heat stable and their necrosis-inducing activity is temperature and light dependent. The in planta activity of CFs was tested by a time series of proteinase K (PK) co-infiltrations, which was unable to affect activity 30min after CF infiltrations. This suggests that the necrosis inducing proteins (NIPs) are either absent from the apoplast and likely actively transported into mesophyll cells or protected from the protease by association with a receptor. Alternatively, plant cell death signaling pathways might be fully engaged during the first 30min and cannot be reversed even after PK treatment. Further fractionation of the CFs with the highest necrosis-inducing activity involved fast performance liquid chromatography, SDS-PAGE and mass spectrometry. This revealed that most of the proteins present in the fractions have not been described before. The two most prominent ZtNIP encoding candidates were heterologously expressed in Pichia pastoris and subsequent infiltration assays showed their differential activity in a range of wheat cultivars.
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http://dx.doi.org/10.1016/j.fgb.2015.03.015DOI Listing
June 2015

Evolutionary analysis of the global landscape of protein domain types and domain architectures associated with family 14 carbohydrate-binding modules.

FEBS Lett 2015 Jul 8;589(15):1813-8. Epub 2015 Jun 8.

Department of Plant Pathology, University of California Davis, Davis, CA, USA. Electronic address:

Domain promiscuity is a powerful evolutionary force that promotes functional innovation in proteins, thus increasing proteome and organismal complexity. Carbohydrate-binding modules, in particular, are known to partake in complex modular architectures that play crucial roles in numerous biochemical and molecular processes. However, the extent, functional, and evolutionary significance of promiscuity is shrouded in mystery for most CBM families. Here, we analyzed the global promiscuity of family 14 carbohydrate-binding modules (CBM14s) and show that fusion, fission, and reorganization events with numerous other domain types interplayed incessantly in a lineage-dependent manner to likely facilitate species adaptation and functional innovation in the family.
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http://dx.doi.org/10.1016/j.febslet.2015.05.048DOI Listing
July 2015

Novel Mutations Detected in Avirulence Genes Overcoming Tomato Cf Resistance Genes in Isolates of a Japanese Population of Cladosporium fulvum.

PLoS One 2015 22;10(4):e0123271. Epub 2015 Apr 22.

Wageningen University, Laboratory of Phytopathology, Wageningen, The Netherlands; Centre for Biosystems Genomics, Wageningen, The Netherlands.

Leaf mold of tomato is caused by the biotrophic fungus Cladosporium fulvum which complies with the gene-for-gene system. The disease was first reported in Japan in the 1920s and has since been frequently observed. Initially only race 0 isolates were reported, but since the consecutive introduction of resistance genes Cf-2, Cf-4, Cf-5 and Cf-9 new races have evolved. Here we first determined the virulence spectrum of 133 C. fulvum isolates collected from 22 prefectures in Japan, and subsequently sequenced the avirulence (Avr) genes Avr2, Avr4, Avr4E, Avr5 and Avr9 to determine the molecular basis of overcoming Cf genes. Twelve races of C. fulvum with a different virulence spectrum were identified, of which races 9, 2.9, 4.9, 4.5.9 and 4.9.11 occur only in Japan. The Avr genes in many of these races contain unique mutations not observed in races identified elsewhere in the world including (i) frameshift mutations and (ii) transposon insertions in Avr2, (iii) point mutations in Avr4 and Avr4E, and (iv) deletions of Avr4E, Avr5 and Avr9. New races have developed by selection pressure imposed by consecutive introductions of Cf-2, Cf-4, Cf-5 and Cf-9 genes in commercially grown tomato cultivars. Our study shows that molecular variations to adapt to different Cf genes in an isolated C. fulvum population in Japan are novel but overall follow similar patterns as those observed in populations from other parts of the world. Implications for breeding of more durable C. fulvum resistant varieties are discussed.
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http://journals.plos.org/plosone/article?id=10.1371/journal.pone.0123271PLOS
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4406682PMC
January 2016

A conserved proline residue in Dothideomycete Avr4 effector proteins is required to trigger a Cf-4-dependent hypersensitive response.

Mol Plant Pathol 2016 Jan 7;17(1):84-95. Epub 2015 May 7.

Laboratory of Phytopathology, Wageningen University, Droevendaalsesteeg 1, 6708 PB, Wageningen, the Netherlands.

CfAvr4, a chitin-binding effector protein produced by the Dothideomycete tomato pathogen Cladosporium fulvum, protects the cell wall of this fungus against hydrolysis by secreted host chitinases during infection. However, in the presence of the Cf-4 immune receptor of tomato, CfAvr4 triggers a hypersensitive response (HR), which renders the pathogen avirulent. Recently, several orthologues of CfAvr4 have been identified from phylogenetically closely related species of Dothideomycete fungi. Of these, DsAvr4 from Dothistroma septosporum also triggers a Cf-4-dependent HR, but CaAvr4 and CbAvr4 from Cercospora apii and Cercospora beticola, respectively, do not. All, however, bind chitin. To identify the region(s) and specific amino acid residue(s) of CfAvr4 and DsAvr4 required to trigger a Cf-4-dependent HR, chimeric and mutant proteins, in which specific protein regions or single amino acid residues, respectively, were exchanged between CfAvr4 and CaAvr4 or DsAvr4 and CbAvr4, were tested for their ability to trigger an HR in Nicotiana benthamiana plants transgenic for the Cf-4 immune receptor gene. Based on this approach, a single region common to CfAvr4 and DsAvr4 was determined to carry a conserved proline residue necessary for the elicitation of this HR. In support of this result, a Cf-4-dependent HR was triggered by mutant CaAvr4 and CbAvr4 proteins carrying an arginine-to-proline substitution at this position. This study provides the first step in deciphering how Avr4 orthologues from different Dothideomycete fungi trigger a Cf-4-dependent HR.
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http://dx.doi.org/10.1111/mpp.12265DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6638486PMC
January 2016

Inter- and intra-domain horizontal gene transfer, gain-loss asymmetry and positive selection mark the evolutionary history of the CBM14 family.

FEBS J 2015 May 23;282(10):2014-28. Epub 2015 Mar 23.

Department of Plant Pathology, University of California Davis, CA, USA.

Protein-carbohydrate interactions are ubiquitous in nature and at the core of many physiological processes of profound importance to health and disease. Specificity in protein-carbohydrate interactions is conferred by carbohydrate-binding modules (CBMs) that can accurately discriminate among the multitude of saccharides found in nature, thus targeting proteins to their particular substrates. Family 14 carbohydrate-binding modules (CBM14s), more specifically, are short modules that bind explicitly to chitin, the second most abundant carbohydrate in nature. Although considerable effort has been placed in elucidating protein-carbohydrate interactions at the molecular level for biological and biotechnological applications, in contrast the evolutionary relationships among these modules are minimally understood. Using the CBM14 family as an example, here we describe one of the first global molecular evolutionary analyses of a CBM family across all domains of life, with an emphasis on its origin, taxonomic distribution and pattern of diversification as a result of gene and module duplication, and positive selection. Our genome-wide searches recovered an impressive number of CBM14s from diverse lineages across nearly all domains of life. However, their highly disseminated distribution in taxa outside the Opisthokonta group strongly suggests a later evolutionary origin and elevated rates of inter- and intra-domain horizontal gene transfer. Moreover, accelerated rates of asymmetric gains and losses reveal a dynamic mode of birth-and-death evolution, whereas positive selection acting on paralogous CBM14-containing proteins suggest changes in substrate specificity and an increase in the functional promiscuity of this ancient CBM family. The importance of these results is discussed.
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http://dx.doi.org/10.1111/febs.13256DOI Listing
May 2015

Cryptic fungal infections: the hidden agenda of plant pathogens.

Front Plant Sci 2014 26;5:506. Epub 2014 Sep 26.

Department of Plant Pathology, University of California Davis Davis, CA, USA.

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http://dx.doi.org/10.3389/fpls.2014.00506DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4176079PMC
October 2014

Positive selection and intragenic recombination contribute to high allelic diversity in effector genes of Mycosphaerella fijiensis, causal agent of the black leaf streak disease of banana.

Mol Plant Pathol 2014 Jun 16;15(5):447-60. Epub 2013 Dec 16.

Department of Plant Pathology, University of California Davis, One Shields Avenue, Davis, CA, 95616-8751, USA; Laboratory of Phytopathology, Wageningen University and Research Centre, Droevendaalsesteeg 1, Wageningen, 6708PB, the Netherlands; Centre for BioSystems Genomics, PO Box 98, Wageningen, 6700 AB, the Netherlands.

Previously, we have determined the nonhost-mediated recognition of the MfAvr4 and MfEcp2 effector proteins from the banana pathogen Mycosphaerella fijiensis in tomato, by the cognate Cf-4 and Cf-Ecp2 resistance proteins, respectively. These two resistance proteins could thus mediate resistance against M. fijiensis if genetically transformed into banana (Musa spp.). However, disease resistance controlled by single dominant genes can be overcome by mutated effector alleles, whose products are not recognized by the cognate resistance proteins. Here, we surveyed the allelic variation within the MfAvr4, MfEcp2, MfEcp2-2 and MfEcp2-3 effector genes of M. fijiensis in a global population of the pathogen, and assayed its impact on recognition by the tomato Cf-4 and Cf-Ecp2 resistance proteins, respectively. We identified a large number of polymorphisms that could reflect a co-evolutionary arms race between host and pathogen. The analysis of nucleotide substitution patterns suggests that both positive selection and intragenic recombination have shaped the evolution of M. fijiensis effectors. Clear differences in allelic diversity were observed between strains originating from South-East Asia relative to strains from other banana-producing continents, consistent with the hypothesis that M. fijiensis originated in the Asian-Pacific region. Furthermore, transient co-expression of the MfAvr4 effector alleles and the tomato Cf-4 resistance gene, as well as of MfEcp2, MfEcp2-2 and MfEcp2-3 and the putative Cf-Ecp2 resistance gene, indicated that effector alleles able to overcome these resistance genes are already present in natural populations of the pathogen, thus questioning the durability of resistance that can be provided by these genes in the field.
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http://dx.doi.org/10.1111/mpp.12104DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6638713PMC
June 2014

The genomes of the fungal plant pathogens Cladosporium fulvum and Dothistroma septosporum reveal adaptation to different hosts and lifestyles but also signatures of common ancestry.

PLoS Genet 2012 29;8(11):e1003088. Epub 2012 Nov 29.

Laboratory of Phytopathology, Wageningen University, Wageningen, The Netherlands.

We sequenced and compared the genomes of the Dothideomycete fungal plant pathogens Cladosporium fulvum (Cfu) (syn. Passalora fulva) and Dothistroma septosporum (Dse) that are closely related phylogenetically, but have different lifestyles and hosts. Although both fungi grow extracellularly in close contact with host mesophyll cells, Cfu is a biotroph infecting tomato, while Dse is a hemibiotroph infecting pine. The genomes of these fungi have a similar set of genes (70% of gene content in both genomes are homologs), but differ significantly in size (Cfu >61.1-Mb; Dse 31.2-Mb), which is mainly due to the difference in repeat content (47.2% in Cfu versus 3.2% in Dse). Recent adaptation to different lifestyles and hosts is suggested by diverged sets of genes. Cfu contains an α-tomatinase gene that we predict might be required for detoxification of tomatine, while this gene is absent in Dse. Many genes encoding secreted proteins are unique to each species and the repeat-rich areas in Cfu are enriched for these species-specific genes. In contrast, conserved genes suggest common host ancestry. Homologs of Cfu effector genes, including Ecp2 and Avr4, are present in Dse and induce a Cf-Ecp2- and Cf-4-mediated hypersensitive response, respectively. Strikingly, genes involved in production of the toxin dothistromin, a likely virulence factor for Dse, are conserved in Cfu, but their expression differs markedly with essentially no expression by Cfu in planta. Likewise, Cfu has a carbohydrate-degrading enzyme catalog that is more similar to that of necrotrophs or hemibiotrophs and a larger pectinolytic gene arsenal than Dse, but many of these genes are not expressed in planta or are pseudogenized. Overall, comparison of their genomes suggests that these closely related plant pathogens had a common ancestral host but since adapted to different hosts and lifestyles by a combination of differentiated gene content, pseudogenization, and gene regulation.
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http://dx.doi.org/10.1371/journal.pgen.1003088DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3510045PMC
May 2013

Phytotoxic secondary metabolites and peptides produced by plant pathogenic Dothideomycete fungi.

FEMS Microbiol Rev 2013 Jan 29;37(1):67-93. Epub 2012 Aug 29.

Department of Plant Pathology, University of California Davis, Davis, CA, USA.

Many necrotrophic plant pathogenic fungi belonging to the class of Dothideomycetes produce phytotoxic metabolites and peptides that are usually required for pathogenicity. Phytotoxins that affect a broad range of plant species are known as non-host-specific toxins (non-HSTs), whereas HSTs affect only a particular plant species or more often genotypes of that species. For pathogens producing HSTs, pathogenicity and host specificity are largely defined by the ability to produce the toxin, while plant susceptibility is dependent on the presence of the toxin target. Non-HSTs are not the main determinants of pathogenicity but contribute to virulence of the producing pathogen. Dothideomycetes are remarkable for the production of toxins, particularly HSTs because they are the only fungal species known so far to produce them. The synthesis, regulation, and mechanisms of action of the most important HSTs and non-HSTs will be discussed. Studies on the mode of action of HSTs have highlighted the induction of programed cell death (PCD) as an important mechanism. We discuss HST-induced PCD and the plant hypersensitive response upon recognition of avirulence factors that share common pathways. In this respect, although nucleotide-binding-site-leucine-rich repeat types of resistance proteins mediate resistance against biotrophs, they can also contribute to susceptibility toward necrotrophs.
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http://dx.doi.org/10.1111/j.1574-6976.2012.00349.xDOI Listing
January 2013

In silico characterization and molecular evolutionary analysis of a novel superfamily of fungal effector proteins.

Mol Biol Evol 2012 Nov 23;29(11):3371-84. Epub 2012 May 23.

Department of Plant Pathology, University of California Davis.

Most fungal plant pathogens secrete effector proteins during pathogenesis to manipulate their host's defense and promote disease. These are so highly diverse in sequence and distribution, they are essentially considered as species-specific. However, we have recently shown the presence of homologous effectors in fungal species of the Dothideomycetes class. One such example is Ecp2, an effector originally described in the tomato pathogen Cladosporium fulvum but later detected in the plant pathogenic fungi Mycosphaerella fijiensis and Mycosphaerella graminicola as well. Here, using in silico sequence-similarity searches against a database of 135 fungal genomes and GenBank, we extend our queries for homologs of Ecp2 to the fungal kingdom and beyond, and further study their history of diversification. Our analyses show that Ecp2 homologs are members of an ancient and widely distributed superfamily of putative fungal effectors, which we term Hce2 for Homologs of C. fulvum Ecp2. Molecular evolutionary analyses show that the superfamily originated and diversified within the fungal kingdom, experiencing multiple lineage-specific expansions and losses that are consistent with the birth-and-death model of gene family evolution. Newly formed paralogs appear to be subject to diversification early after gene duplication events, whereas at later stages purifying selection acts to preserve diversity and the newly evolved putative functions. Some members of the Hce2 superfamily are fused to fungal Glycoside Hydrolase family 18 chitinases that show high similarity to the Zymocin killer toxin from the dairy yeast Kluyveromyces lactis, suggesting an analogous role in antagonistic interactions. The observed high rates of gene duplication and loss in the Hce2 superfamily, combined with diversification in both sequence and possibly functions within and between species, suggest that Hce2s are involved in adaptation to stresses and new ecological niches. Such findings address the need to rationalize effector biology and evolution beyond the perspective of solely host-microbe interactions.
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http://dx.doi.org/10.1093/molbev/mss143DOI Listing
November 2012

Finished genome of the fungal wheat pathogen Mycosphaerella graminicola reveals dispensome structure, chromosome plasticity, and stealth pathogenesis.

PLoS Genet 2011 Jun 9;7(6):e1002070. Epub 2011 Jun 9.

USDA-Agricultural Research Service, Purdue University, West Lafayette, Indiana, United States of America.

The plant-pathogenic fungus Mycosphaerella graminicola (asexual stage: Septoria tritici) causes septoria tritici blotch, a disease that greatly reduces the yield and quality of wheat. This disease is economically important in most wheat-growing areas worldwide and threatens global food production. Control of the disease has been hampered by a limited understanding of the genetic and biochemical bases of pathogenicity, including mechanisms of infection and of resistance in the host. Unlike most other plant pathogens, M. graminicola has a long latent period during which it evades host defenses. Although this type of stealth pathogenicity occurs commonly in Mycosphaerella and other Dothideomycetes, the largest class of plant-pathogenic fungi, its genetic basis is not known. To address this problem, the genome of M. graminicola was sequenced completely. The finished genome contains 21 chromosomes, eight of which could be lost with no visible effect on the fungus and thus are dispensable. This eight-chromosome dispensome is dynamic in field and progeny isolates, is different from the core genome in gene and repeat content, and appears to have originated by ancient horizontal transfer from an unknown donor. Synteny plots of the M. graminicola chromosomes versus those of the only other sequenced Dothideomycete, Stagonospora nodorum, revealed conservation of gene content but not order or orientation, suggesting a high rate of intra-chromosomal rearrangement in one or both species. This observed "mesosynteny" is very different from synteny seen between other organisms. A surprising feature of the M. graminicola genome compared to other sequenced plant pathogens was that it contained very few genes for enzymes that break down plant cell walls, which was more similar to endophytes than to pathogens. The stealth pathogenesis of M. graminicola probably involves degradation of proteins rather than carbohydrates to evade host defenses during the biotrophic stage of infection and may have evolved from endophytic ancestors.
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http://dx.doi.org/10.1371/journal.pgen.1002070DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3111534PMC
June 2011

Horizontal gene and chromosome transfer in plant pathogenic fungi affecting host range.

FEMS Microbiol Rev 2011 May 26;35(3):542-54. Epub 2011 Jan 26.

Laboratory of Phytopathology, Wageningen University, Wageningen, The Netherlands.

Plant pathogenic fungi adapt quickly to changing environments including overcoming plant disease resistance genes. This is usually achieved by mutations in single effector genes of the pathogens, enabling them to avoid recognition by the host plant. In addition, horizontal gene transfer (HGT) and horizontal chromosome transfer (HCT) provide a means for pathogens to broaden their host range. Recently, several reports have appeared in the literature on HGT, HCT and hybridization between plant pathogenic fungi that affect their host range, including species of Stagonospora/Pyrenophora, Fusarium and Alternaria. Evidence is given that HGT of the ToxA gene from Stagonospora nodorum to Pyrenophora tritici-repentis enabled the latter fungus to cause a serious disease in wheat. A nonpathogenic Fusarium species can become pathogenic on tomato by HCT of a pathogenicity chromosome from Fusarium oxysporum f.sp lycopersici, a well-known pathogen of tomato. Similarly, Alternaria species can broaden their host range by HCT of a single chromosome carrying a cluster of genes encoding host-specific toxins that enabled them to become pathogenic on new hosts such as apple, Japanese pear, strawberry and tomato, respectively. The mechanisms HGT and HCT and their impact on potential emergence of fungal plant pathogens adapted to new host plants will be discussed.
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http://dx.doi.org/10.1111/j.1574-6976.2010.00263.xDOI Listing
May 2011

Tomato Cf resistance proteins mediate recognition of cognate homologous effectors from fungi pathogenic on dicots and monocots.

Proc Natl Acad Sci U S A 2010 Apr 5;107(16):7610-5. Epub 2010 Apr 5.

Laboratory of Phytopathology, Wageningen University and Research Centre, 6708 PB, Wageningen, The Netherlands.

Most fungal effectors characterized so far are species-specific and facilitate virulence on a particular host plant. During infection of its host tomato, Cladosporium fulvum secretes effectors that function as virulence factors in the absence of cognate Cf resistance proteins and induce effector-triggered immunity in their presence. Here we show that homologs of the C. fulvum Avr4 and Ecp2 effectors are present in other pathogenic fungi of the Dothideomycete class, including Mycosphaerella fijiensis, the causal agent of black Sigatoka disease of banana. We demonstrate that the Avr4 homolog of M. fijiensis is a functional ortholog of C. fulvum Avr4 that protects fungal cell walls against hydrolysis by plant chitinases through binding to chitin and, despite the low overall sequence homology, triggers a Cf-4-mediated hypersensitive response (HR) in tomato. Furthermore, three homologs of C. fulvum Ecp2 are found in M. fijiensis, one of which induces different levels of necrosis or HR in tomato lines that lack or contain a putative cognate Cf-Ecp2 protein, respectively. In contrast to Avr4, which acts as a defensive virulence factor, M. fijiensis Ecp2 likely promotes virulence by interacting with a putative host target causing host cell necrosis, whereas Cf-Ecp2 could possibly guard the virulence target of Ecp2 and trigger a Cf-Ecp2-mediated HR. Overall our data suggest that Avr4 and Ecp2 represent core effectors that are collectively recognized by single cognate Cf-proteins. Transfer of these Cf genes to plant species that are attacked by fungi containing these cognate core effectors provides unique ways for breeding disease-resistant crops.
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http://dx.doi.org/10.1073/pnas.1002910107DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC2867746PMC
April 2010

Fungal effector proteins: past, present and future.

Mol Plant Pathol 2009 Nov;10(6):735-47

Wageningen University and Research Centre, Laboratory of Phytopathology, Droevendaalsesteeg 1, 6708 PB Wageningen, the Netherlands.

The pioneering research of Harold Flor on flax and the flax rust fungus culminated in his gene-for-gene hypothesis. It took nearly 50 years before the first fungal avirulence (Avr) gene in support of his hypothesis was cloned. Initially, fungal Avr genes were identified by reverse genetics and map-based cloning from model organisms, but, currently, the availability of many sequenced fungal genomes allows their cloning from additional fungi by a combination of comparative and functional genomics. It is believed that most Avr genes encode effectors that facilitate virulence by suppressing pathogen-associated molecular pattern-triggered immunity and induce effector-triggered immunity in plants containing cognate resistance proteins. In resistant plants, effectors are directly or indirectly recognized by cognate resistance proteins that reside either on the plasma membrane or inside the plant cell. Indirect recognition of an effector (also known as the guard model) implies that the virulence target of an effector in the host (the guardee) is guarded by the resistance protein (the guard) that senses manipulation of the guardee, leading to activation of effector-triggered immunity. In this article, we review the literature on fungal effectors and some pathogen-associated molecular patterns, including those of some fungi for which no gene-for-gene relationship has been established.
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http://dx.doi.org/10.1111/j.1364-3703.2009.00591.xDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6640362PMC
November 2009