Article

Comparative large-scale analysis of interactions between several crop species and the effector repertoires from multiple pathovars of Pseudomonas and Ralstonia.

Genome Center and Department of Plant Sciences, University of California, Davis, California 95616, USA.
Plant physiology (Impact Factor: 6.56). 08/2009; 150(4):1733-49. DOI: 10.1104/pp.109.140251
Source: PubMed

ABSTRACT Bacterial plant pathogens manipulate their hosts by injection of numerous effector proteins into host cells via type III secretion systems. Recognition of these effectors by the host plant leads to the induction of a defense reaction that often culminates in a hypersensitive response manifested as cell death. Genes encoding effector proteins can be exchanged between different strains of bacteria via horizontal transfer, and often individual strains are capable of infecting multiple hosts. Host plant species express diverse repertoires of resistance proteins that mediate direct or indirect recognition of bacterial effectors. As a result, plants and their bacterial pathogens should be considered as two extensive coevolving groups rather than as individual host species coevolving with single pathovars. To dissect the complexity of this coevolution, we cloned 171 effector-encoding genes from several pathovars of Pseudomonas and Ralstonia. We used Agrobacterium tumefaciens-mediated transient assays to test the ability of each effector to induce a necrotic phenotype on 59 plant genotypes belonging to four plant families, including numerous diverse accessions of lettuce (Lactuca sativa) and tomato (Solanum lycopersicum). Known defense-inducing effectors (avirulence factors) and their homologs commonly induced extensive necrosis in many different plant species. Nonhost species reacted to multiple effector proteins from an individual pathovar more frequently and more intensely than host species. Both homologous and sequence-unrelated effectors could elicit necrosis in a similar spectrum of plants, suggesting common effector targets or targeting of the same pathways in the plant cell.

0 Bookmarks
 · 
94 Views
  • [Show abstract] [Hide abstract]
    ABSTRACT: Bacterial flagellin is perceived as a microbe (or pathogen)-associated molecular pattern (MAMP or PAMP) by the extracellular pattern recognition receptors, FLS2 and TLR5, of plants and mammals, respectively. Flagellin accidently translocated into mammalian cells by pathogen type III secretion systems (T3SSs) is recognized by nucleotide-binding leucine-rich repeat receptor NLRC4 as a pattern of pathogenesis and induces a death-associated immune response. The nonpathogen Pseudomonas fluorescens Pf0-1, expressing a Pseudomonas syringae T3SS, and the plant pathogen P. syringae pv. tomato DC3000 were used to seek evidence of an analogous cytoplasmic recognition system for flagellin in the model plant Nicotiana benthamiana. Flagellin (FliC) was secreted in culture and translocated into plant cells by the T3SS expressed in Pf0-1 and DC3000 and in their ΔflgGHI flagellar pathway mutants. ΔfliC and ΔflgGHI mutants of Pf0-1 and DC3000 were strongly reduced in elicitation of reactive oxygen species production and in immunity induction as indicated by the ability of challenge bacteria inoculated 6 h later to translocate a type III effector-reporter and to elicit effector-triggered cell death. Agrobacterium-mediated transient expression in N. benthamiana of FliC with or without a eukaryotic export signal peptide, coupled with virus-induced gene silencing of FLS2, revealed no immune response that was not FLS2 dependent. Transiently expressed FliC from DC3000 and Pectobacterium carotovorum did not induce cell death in N. benthamiana, tobacco, or tomato leaves. Flagellin is the major Pseudomonas MAMP perceived by N. benthamiana, and although flagellin secretion through the plant cell wall by the T3SS may partially contribute to FLS2-dependent immunity, flagellin in the cytosol does not elicit immune-associated cell death. We postulate that a death response to translocated MAMPs would produce vulnerability to the many necrotrophic pathogens of plants, such as P. carotovorum, which differ from P. syringae and other (hemi)biotrophic pathogens in benefitting from death-associated immune responses.
    Cellular Microbiology 10/2012; · 4.81 Impact Factor
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: The discovery in the mid-80s of contiguous gene clusters that were later shown to code for a novel protein secretion system has been a milestone in plant pathology and the study of plantbacterial interactions. This system, named type III secretion system (T3SS), is dedicated to the translocation of virulence-related proteins, called effectors, from the pathogen to the host and is common among phytopathogenic, zoopathogenic and symbiotic bacteria. Bacterial pathogens overcome multiple layers of plant defense, both preformed barriers and inducible mechanisms. To accomplish this they deploy sophisticated molecular devices to secrete selected sets of proteins either to the intercellular spaces or directly inside the plant cell. Such proteins enable pathogens to avoid recognition, block induction of immune responses and/or interfere with the defense signaling network. Recent developments in molecular biology facilitated research on these interactions and rendered the interkingdom trafficking of proteins a key element of pathogenicity, virulence and host specificity of Gramnegative bacterial pathogens. While basic research on phytobacterial pathogens has progressed, little has changed on the crop protection schemes against bacterial infections. In this review, we summarize the latest findings on the different levels at which contact-dependent protein secretion from Gram-negative bacteria subverts and/or manipulates plant immunity. Additionally, we focus on the biotechnological applications which have emerged from basic research on phytobacterial T3SS and its cognate effectors, ranging from bacterial diagnostics, plant resistance and anti-virulence chemicals to toolkits for gene targeting in plants.
    Hellenic Plant Protection Journal 01/2012; 5(2).
  • Source
    [Show abstract] [Hide abstract]
    ABSTRACT: Nonhost resistance is a broad-spectrum plant defense that provides immunity to all members of a plant species against all isolates of a microorganism that is pathogenic to other plant species. Upon landing on the surface of a nonhost plant species, a potential bacterial pathogen initially encounters preformed and, later, induced plant defenses. One of the initial defense responses from the plant is pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). Nonhost plants also have mechanisms to detect nonhost-pathogen effectors and can trigger a defense response referred to as effector-triggered immunity (ETI). This nonhost resistance response often results in a hypersensitive response (HR) at the infection site. This review provides an overview of these plant defense strategies. We enumerate plant genes that impart nonhost resistance and the bacterial counter-defense strategies. In addition, prospects for application of nonhost resistance to achieve broad-spectrum and durable resistance in crop plants are also discussed. Expected final online publication date for the Annual Review of Phytopathology Volume 51 is August 04, 2013. Please see http://www.annualreviews.org/catalog/pubdates.aspx for revised estimates.
    Annual Review of Phytopathology 05/2013; · 10.23 Impact Factor

Full-text (2 Sources)

View
14 Downloads
Available from
Jun 2, 2014