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Common and contrasting themes in host cell-targeted effectors from bacterial, fungal, oomycete and nematode plant symbionts described using the Gene Ontology.

Torto-Alalibo T, Collmer CW, Lindeberg M, Bird D, Collmer A, Tyler BM - BMC Microbiol. (2009)

Bottom Line: A wide diversity of plant-associated symbionts, including microbes, produce proteins that can enter host cells, or are injected into host cells in order to modify the physiology of the host to promote colonization.Effectors from diverse symbionts may be delivered into plant cells via varied mechanisms, including whole organism cellular entry (viruses, some bacteria and fungi), type III and IV secretion (in bacteria), physical injection (nematodes and insects) and protein translocation signal sequences (oomycetes and fungi).This mini-review will summarize both similarities and differences in effectors and effector delivery systems found in diverse plant-associated symbionts as well as how these are described with Plant-Associated Microbe Gene Ontology (PAMGO) terms.

View Article: PubMed Central - HTML - PubMed

Affiliation: Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA. trudy@vbi.vt.edu

ABSTRACT
A wide diversity of plant-associated symbionts, including microbes, produce proteins that can enter host cells, or are injected into host cells in order to modify the physiology of the host to promote colonization. These molecules, termed effectors, commonly target the host defense signaling pathways in order to suppress the defense response. Others target the gene expression machinery or trigger specific modifications to host morphology or physiology that promote the nutrition and proliferation of the symbiont. When recognized by the host's surveillance machinery, which includes cognate resistance (R) gene products, defense responses are engaged to restrict pathogen proliferation. Effectors from diverse symbionts may be delivered into plant cells via varied mechanisms, including whole organism cellular entry (viruses, some bacteria and fungi), type III and IV secretion (in bacteria), physical injection (nematodes and insects) and protein translocation signal sequences (oomycetes and fungi). This mini-review will summarize both similarities and differences in effectors and effector delivery systems found in diverse plant-associated symbionts as well as how these are described with Plant-Associated Microbe Gene Ontology (PAMGO) terms.

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Effector delivery structures of Gram-negative bacterium, oomycete, fungus, and nematode in plant cell. (A) Type III secretion system in Gram-negative bacterium injects effectors into the host cell. (B) The haustorium in biotrophic and hemibiotrophic filamentous pathogens is believed to be the site of effector release into the host cell. (C) Gland secretions, which include effectors, are injected into the plant cell via the stylet of the nematode. Effectors (E) thus delivered, can either suppress host defenses and/or trigger host cell defenses, which include programmed cell death (PCD) upon recognition by resistance (R) proteins. Recognition of effectors by R proteins may occur directly (observed with some fungal effectors) or indirectly as a result of interaction of the effectors with other host protein(s) (observed with a number of bacterial effectors). Potential subcellular locations of effectors such as the nucleus and chloroplasts are also shown.
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Figure 1: Effector delivery structures of Gram-negative bacterium, oomycete, fungus, and nematode in plant cell. (A) Type III secretion system in Gram-negative bacterium injects effectors into the host cell. (B) The haustorium in biotrophic and hemibiotrophic filamentous pathogens is believed to be the site of effector release into the host cell. (C) Gland secretions, which include effectors, are injected into the plant cell via the stylet of the nematode. Effectors (E) thus delivered, can either suppress host defenses and/or trigger host cell defenses, which include programmed cell death (PCD) upon recognition by resistance (R) proteins. Recognition of effectors by R proteins may occur directly (observed with some fungal effectors) or indirectly as a result of interaction of the effectors with other host protein(s) (observed with a number of bacterial effectors). Potential subcellular locations of effectors such as the nucleus and chloroplasts are also shown.

Mentions: Critical to effector function is their successful delivery to their site of action in the host cell. For the pathogens discussed here, this process involves passage across the plant cell wall and the plasma membrane. The injectisomes of bacterial type III and type IV secretion systems (T3SS and T4SS) respectively; (reviewed in [6,37-39]) are analogous to the stylets of plant parasitic nematodes. Also known as the Hrp pilus, the T3SS injectisome spans both the bacterial envelope and the plant cell wall, forming a channel between the bacterial cytoplasm and the host plasma cell membrane. Secreted proteins delivered by the injectisome then form a pore through the membrane that enables translocation of effector proteins into the host cell (Figure 1a) [5]. The stylet in nematodes executes an analogous function, in that it mechanically pierces the host cell wall but not the membrane and injects gland secretions, including effectors, into the host cell cytoplasm via an orifice at the tip of the stylet (Figure 1c) [31,40].


Common and contrasting themes in host cell-targeted effectors from bacterial, fungal, oomycete and nematode plant symbionts described using the Gene Ontology.

Torto-Alalibo T, Collmer CW, Lindeberg M, Bird D, Collmer A, Tyler BM - BMC Microbiol. (2009)

Effector delivery structures of Gram-negative bacterium, oomycete, fungus, and nematode in plant cell. (A) Type III secretion system in Gram-negative bacterium injects effectors into the host cell. (B) The haustorium in biotrophic and hemibiotrophic filamentous pathogens is believed to be the site of effector release into the host cell. (C) Gland secretions, which include effectors, are injected into the plant cell via the stylet of the nematode. Effectors (E) thus delivered, can either suppress host defenses and/or trigger host cell defenses, which include programmed cell death (PCD) upon recognition by resistance (R) proteins. Recognition of effectors by R proteins may occur directly (observed with some fungal effectors) or indirectly as a result of interaction of the effectors with other host protein(s) (observed with a number of bacterial effectors). Potential subcellular locations of effectors such as the nucleus and chloroplasts are also shown.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2654663&req=5

Figure 1: Effector delivery structures of Gram-negative bacterium, oomycete, fungus, and nematode in plant cell. (A) Type III secretion system in Gram-negative bacterium injects effectors into the host cell. (B) The haustorium in biotrophic and hemibiotrophic filamentous pathogens is believed to be the site of effector release into the host cell. (C) Gland secretions, which include effectors, are injected into the plant cell via the stylet of the nematode. Effectors (E) thus delivered, can either suppress host defenses and/or trigger host cell defenses, which include programmed cell death (PCD) upon recognition by resistance (R) proteins. Recognition of effectors by R proteins may occur directly (observed with some fungal effectors) or indirectly as a result of interaction of the effectors with other host protein(s) (observed with a number of bacterial effectors). Potential subcellular locations of effectors such as the nucleus and chloroplasts are also shown.
Mentions: Critical to effector function is their successful delivery to their site of action in the host cell. For the pathogens discussed here, this process involves passage across the plant cell wall and the plasma membrane. The injectisomes of bacterial type III and type IV secretion systems (T3SS and T4SS) respectively; (reviewed in [6,37-39]) are analogous to the stylets of plant parasitic nematodes. Also known as the Hrp pilus, the T3SS injectisome spans both the bacterial envelope and the plant cell wall, forming a channel between the bacterial cytoplasm and the host plasma cell membrane. Secreted proteins delivered by the injectisome then form a pore through the membrane that enables translocation of effector proteins into the host cell (Figure 1a) [5]. The stylet in nematodes executes an analogous function, in that it mechanically pierces the host cell wall but not the membrane and injects gland secretions, including effectors, into the host cell cytoplasm via an orifice at the tip of the stylet (Figure 1c) [31,40].

Bottom Line: A wide diversity of plant-associated symbionts, including microbes, produce proteins that can enter host cells, or are injected into host cells in order to modify the physiology of the host to promote colonization.Effectors from diverse symbionts may be delivered into plant cells via varied mechanisms, including whole organism cellular entry (viruses, some bacteria and fungi), type III and IV secretion (in bacteria), physical injection (nematodes and insects) and protein translocation signal sequences (oomycetes and fungi).This mini-review will summarize both similarities and differences in effectors and effector delivery systems found in diverse plant-associated symbionts as well as how these are described with Plant-Associated Microbe Gene Ontology (PAMGO) terms.

View Article: PubMed Central - HTML - PubMed

Affiliation: Virginia Bioinformatics Institute, Virginia Polytechnic Institute and State University, Blacksburg, VA 24061, USA. trudy@vbi.vt.edu

ABSTRACT
A wide diversity of plant-associated symbionts, including microbes, produce proteins that can enter host cells, or are injected into host cells in order to modify the physiology of the host to promote colonization. These molecules, termed effectors, commonly target the host defense signaling pathways in order to suppress the defense response. Others target the gene expression machinery or trigger specific modifications to host morphology or physiology that promote the nutrition and proliferation of the symbiont. When recognized by the host's surveillance machinery, which includes cognate resistance (R) gene products, defense responses are engaged to restrict pathogen proliferation. Effectors from diverse symbionts may be delivered into plant cells via varied mechanisms, including whole organism cellular entry (viruses, some bacteria and fungi), type III and IV secretion (in bacteria), physical injection (nematodes and insects) and protein translocation signal sequences (oomycetes and fungi). This mini-review will summarize both similarities and differences in effectors and effector delivery systems found in diverse plant-associated symbionts as well as how these are described with Plant-Associated Microbe Gene Ontology (PAMGO) terms.

Show MeSH
Related in: MedlinePlus