plant Microbe Interaction
18 views | +0 today
Follow
Your new post is loading...
Your new post is loading...
Rescooped by Wenjun Zhu from Plants and Microbes
Scoop.it!

PLOS Pathogens: A Pathogen Type III Effector with a Novel E3 Ubiquitin Ligase Architecture (2013)

PLOS Pathogens: A Pathogen Type III Effector with a Novel E3 Ubiquitin Ligase Architecture (2013) | plant Microbe Interaction | Scoop.it

Type III effectors are virulence factors of Gram-negative bacterial pathogens delivered directly into host cells by the type III secretion nanomachine where they manipulate host cell processes such as the innate immunity and gene expression. Here, we show that the novel type III effector XopL from the model plant pathogen Xanthomonas campestris pv. vesicatoriaexhibits E3 ubiquitin ligase activity in vitro and in planta, induces plant cell death and subverts plant immunity. E3 ligase activity is associated with the C-terminal region of XopL, which specifically interacts with plant E2 ubiquitin conjugating enzymes and mediates formation of predominantly K11-linked polyubiquitin chains. The crystal structure of the XopL C-terminal domain revealed a single domain with a novel fold, termed XL-box, not present in any previously characterized E3 ligase. Mutation of amino acids in the central cavity of the XL-box disrupts E3 ligase activity and prevents XopL-induced plant cell death. The lack of cysteine residues in the XL-box suggests the absence of thioester-linked ubiquitin-E3 ligase intermediates and a non-catalytic mechanism for XopL-mediated ubiquitination. The crystal structure of the N-terminal region of XopL confirmed the presence of a leucine-rich repeat (LRR) domain, which may serve as a protein-protein interaction module for ubiquitination target recognition. While the E3 ligase activity is required to provoke plant cell death, suppression of PAMP responses solely depends on the N-terminal LRR domain. Taken together, the unique structural fold of the E3 ubiquitin ligase domain within the Xanthomonas XopL is unprecedented and highlights the variation in bacterial pathogen effectors mimicking this eukaryote-specific activity.


Via Kamoun Lab @ TSL
more...
No comment yet.
Rescooped by Wenjun Zhu from Plants and Microbes
Scoop.it!

PNAS: NADPH oxidases regulate septin-mediated cytoskeletal remodeling during plant infection by the rice blast fungus (2013)

PNAS: NADPH oxidases regulate septin-mediated cytoskeletal remodeling during plant infection by the rice blast fungus (2013) | plant Microbe Interaction | Scoop.it

The rice blast fungus Magnaporthe oryzae infects plants with a specialized cell called an appressorium, which uses turgor to drive a rigid penetration peg through the rice leaf cuticle. Here, we show that NADPH oxidases (Nox) are necessary for septin-mediated reorientation of the F-actin cytoskeleton to facilitate cuticle rupture and plant cell invasion. We report that the Nox2–NoxR complex spatially organizes a heteroligomeric septin ring at the appressorium pore, required for assembly of a toroidal F-actin network at the point of penetration peg emergence. Maintenance of the cortical F-actin network during plant infection independently requires Nox1, a second NADPH oxidase, which is necessary for penetration hypha elongation. Organization of F-actin in appressoria is disrupted by application of antioxidants, whereas latrunculin-mediated depolymerization of appressorial F-actin is competitively inhibited by reactive oxygen species, providing evidence that regulated synthesis of reactive oxygen species by fungal NADPH oxidases directly controls septin and F-actin dynamics.


Via Elsa Ballini, Kamoun Lab @ TSL
more...
No comment yet.
Rescooped by Wenjun Zhu from Host Translocation of Plant Pathogen Effectors
Scoop.it!

Metabolic priming by a secreted fungal effector. Nature (2011)

Metabolic priming by a secreted fungal effector. Nature (2011) | plant Microbe Interaction | Scoop.it

To localize Cmu1 during biotrophic growth, plants were infected with SG200Dcmu1-cmu1–HA, which carries a cmu1–HA fusion gene inserted in single copy under control of its native promoter. Plants infected with SG200 or with SG200 Pcmu1GFP–HA expressing cytoplasmic green fluorescent protein (GFP) under the cmu1 promoter served as negative controls. Freeze-substituted and resin-embedded sections of maize tissue harvested 3 days after infection with these strains were incubated with anti-HA antibodies and gold markers. Cmu1–HA could be detected inside the fungal hyphae, in the biotrophic interface as well as inside the plant cytoplasm but rarely in the plant cell wall (Fig. 2A and Supplementary Fig. 7). The distribution of gold particles was quantified (Fig. 2B). Gold labelling of plant tissue infected with the parental strain SG200 was negligible (Supplementary Fig. 8), whereas non-secreted GFP–HA was absent from the biotrophic interphase, showed strong accumulation in the fungal cytosol and weak background labelling in the plant cytosol (Supplementary Fig. 9 and Fig. 2B).


Via Kamoun Lab @ TSL
more...
No comment yet.
Rescooped by Wenjun Zhu from Plants and Microbes
Scoop.it!

PLOS Pathogens: The Tomato Prf Complex Is a Molecular Trap for Bacterial Effectors Based on Pto Transphosphorylation (2013)

PLOS Pathogens: The Tomato Prf Complex Is a Molecular Trap for Bacterial Effectors Based on Pto Transphosphorylation (2013) | plant Microbe Interaction | Scoop.it

The major virulence strategy of phytopathogenic bacteria is to secrete effector proteins into the host cell to target the immune machinery. AvrPto and AvrPtoB are two such effectors fromPseudomonas syringae, which disable an overlapping range of kinases in Arabidopsis and Tomato. Both effectors target surface-localized receptor-kinases to avoid bacterial recognition. In turn, tomato has evolved an intracellular effector-recognition complex composed of the NB-LRR protein Prf and the Pto kinase. Structural analyses have shown that the most important interaction surface for AvrPto and AvrPtoB is the Pto P+1 loop. AvrPto is an inhibitor of Pto kinase activity, but paradoxically, this kinase activity is a prerequisite for defense activation by AvrPto. Here using biochemical approaches we show that disruption of Pto P+1 loop stimulates phosphorylation in trans, which is possible because the Pto/Prf complex is oligomeric. Both P+1 loop disruption and transphosphorylation are necessary for signalling. Thus, effector perturbation of one kinase molecule in the complex activates another. Hence, the Pto/Prf complex is a sophisticated molecular trap for effectors that target protein kinases, an essential aspect of the pathogen's virulence strategy. The data presented here give a clear view of why bacterial virulence and host recognition mechanisms are so often related and how the slowly evolving host is able to keep pace with the faster-evolving pathogen.


Via Kamoun Lab @ TSL
more...
No comment yet.
Rescooped by Wenjun Zhu from Plants and Microbes
Scoop.it!

Nature Genetics: Oomycete pathogens encode RNA silencing suppressors (2013)

Nature Genetics: Oomycete pathogens encode RNA silencing suppressors (2013) | plant Microbe Interaction | Scoop.it

Effectors are essential virulence proteins produced by a broad range of parasites, including viruses, bacteria, fungi, oomycetes, protozoa, insects and nematodes. Upon entry into host cells, pathogen effectors manipulate specific physiological processes or signaling pathways to subvert host immunity. Most effectors, especially those of eukaryotic pathogens, remain functionally uncharacterized. Here, we show that two effectors from the oomycete plant pathogen Phytophthora sojae suppress RNA silencing in plants by inhibiting the biogenesis of small RNAs. Ectopic expression of thesePhytophthora suppressors of RNA silencing enhances plant susceptibility to both a virus and Phytophthora, showing that some eukaryotic pathogens have evolved virulence proteins that target host RNA silencing processes to promote infection. These findings identify RNA silencing suppression as a common strategy used by pathogens across kingdoms to cause disease and are consistent with RNA silencing having key roles in host defense.


Via Kamoun Lab @ TSL
more...
No comment yet.