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2.  Sequential Delivery of Host-Induced Virulence Effectors by Appressoria and Intracellular Hyphae of the Phytopathogen Colletotrichum higginsianum 
PLoS Pathogens  2012;8(4):e1002643.
Phytopathogens secrete effector proteins to manipulate their hosts for effective colonization. Hemibiotrophic fungi must maintain host viability during initial biotrophic growth and elicit host death for subsequent necrotrophic growth. To identify effectors mediating these opposing processes, we deeply sequenced the transcriptome of Colletotrichum higginsianum infecting Arabidopsis. Most effector genes are host-induced and expressed in consecutive waves associated with pathogenic transitions, indicating distinct effector suites are deployed at each stage. Using fluorescent protein tagging and transmission electron microscopy-immunogold labelling, we found effectors localised to stage-specific compartments at the host-pathogen interface. In particular, we show effectors are focally secreted from appressorial penetration pores before host invasion, revealing new levels of functional complexity for this fungal organ. Furthermore, we demonstrate that antagonistic effectors either induce or suppress plant cell death. Based on these results we conclude that hemibiotrophy in Colletotrichum is orchestrated through the coordinated expression of antagonistic effectors supporting either cell viability or cell death.
Author Summary
Many fungal plant pathogens undergo a series of developmental and morphological transitions required for successful host invasion. For example, Colletotrichum higginsianum, a pathogen of cruciferous plants, employs a two-stage infection strategy called ‘hemibiotrophy’: after specialized penetration organs (appressoria) breach the host cuticle and cell wall, the fungus initially produces bulbous primary hyphae inside living epidermal cells (‘biotrophy’), before entering a destructive phase in which host tissues are killed and macerated by filamentous secondary hyphae (‘necrotrophy’). Here we investigated the role of secreted effector proteins in mediating hemibiotrophy and their delivery at fungal-plant interfaces. We found expression of many effector genes is plant-induced and distinct sets of effectors are deployed in successive waves by particular fungal cell-types. Early-expressed effector proteins are focally secreted from appressorial penetration pores and may function to suppress early plant defense responses, which we found to be activated before fungal entry. We also show that later-expressed effectors accumulate in structures formed at the interface between primary hyphae and living host cells, implicating these hyphae in effector delivery. Our findings indicate new functions for fungal infection structures and suggest a model for how this fungus switches from biotrophy to necrotrophy.
PMCID: PMC3320591  PMID: 22496661
3.  HvCEBiP, a gene homologous to rice chitin receptor CEBiP, contributes to basal resistance of barley to Magnaporthe oryzae 
BMC Plant Biology  2010;10:288.
Rice CEBiP recognizes chitin oligosaccharides on the fungal cell surface or released into the plant apoplast, leading to the expression of plant disease resistance against fungal infection. However, it has not yet been reported whether CEBiP is actually required for restricting the growth of fungal pathogens. Here we evaluated the involvement of a putative chitin receptor gene in the basal resistance of barley to the ssd1 mutant of Magnaporthe oryzae, which induces multiple host defense responses.
The mossd1 mutant showed attenuated pathogenicity on barley and appressorial penetration was restricted by the formation of callose papillae at attempted entry sites. When conidial suspensions of mossd1 mutant were spotted onto the leaves of HvCEBiP-silenced plants, small brown necrotic flecks or blast lesions were produced but these lesions did not expand beyond the inoculation site. Wild-type M. oryzae also produced slightly more severe symptoms on the leaves of HvCEBiP-silenced plants. Cytological observation revealed that these lesions resulted from appressorium-mediated penetration into plant epidermal cells.
These results suggest that HvCEBiP is involved in basal resistance against appressorium-mediated infection and that basal resistance might be triggered by the recognition of chitin oligosaccharides derived from M. oryzae.
PMCID: PMC3020183  PMID: 21190588
4.  Colletotrichum: species, ecology and interactions 
The presentations of the Special Interest Group meeting Colletotrichum: species, ecology and interactions, held on 1 August 2010 during IMC9 in Edinburgh, UK, are outlined. Seven research projects, ranged from systematics and population genetics to host-pathogen interactions and genome projects were presented. The meeting revealed that currently major species complexes in the genus Colletotrichum are being revised and the identities of many pathogens clarified on the basis of molecular phylogenies, and that the genomes of four species are sequenced and decoded providing an enormous amount of data that are used to increase our understanding of the biology of Colletotrichum species.
PMCID: PMC3348780  PMID: 22679575
genome sequencing; host-pathogen interaction; identification; pathogenicity; population genetics; systematics
5.  Immunomagnetic Purification of Colletotrichum lindemuthianum Appressoria 
We developed a method to purify appressoria of the bean anthracnose fungus Colletotrichum lindemuthianum for biochemical analysis of the cell surface and to compare appressoria with other fungal structures. We used immunomagnetic separation after incubation of infected bean leaf homogenates with a monoclonal antibody that binds strongly to the appressoria. Preparations with a purity of >90% could be obtained. Examination of the purified appressoria by transmission electron microscopy showed that most had lost their cytoplasm. However, the plasma membrane was retained, suggesting that there is some form of attachment of this membrane to the cell wall. The purified appressoria can be used for studies of their cell surface, and we have shown that there are clear differences in the glycoprotein constituents of cell walls of appressoria compared with mycelium.
PMCID: PMC92171  PMID: 10919807
6.  Tendon Injuries: Surgery or Not? 
Canadian Family Physician  1979;25:588-590.
Early recognition of major tendon disruption is within the clinical expertise of the family doctor. The treatment of most major tendon injuries is early surgical repair.
PMCID: PMC2383110  PMID: 21297740

Results 1-6 (6)