Multiple candidate effectors from the oomycete pathogen hyaloperonospora arabidopsidis suppress host plant immunity

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DOIResolve DOI: http://doi.org/10.1371/journal.ppat.1002348
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TypeArticle
Journal titlePLoS Pathogens
ISSN1553-7366
Volume7
Issue11
Article numbere1002348
SubjectArabidopsis; article; gene sequence; genome analysis; Hyaloperonosspora arabidopsidis; nonhuman; Oomycetes; pathogenesis; plant disease; plant growth; plant immunity; Pseudomonas syringae; tomato; virulence; Arabidopsis; bacterial secretion system; biosynthesis; cell culture; enzymology; gene expression regulation; genetics; growth, development and aging; host pathogen interaction; immunology; metabolism; microbiology; plant disease; Pseudomonas syringae; rapeseed; transgenic plant; Arabidopsis; Arabidopsis thaliana; Bacteria (microorganisms); Brassica rapa subsp. rapa; Eukaryota; Hyaloperonospora; Lycopersicon esculentum; Peronosporaceae; Pseudomonas syringae; callose; glucan; hybrid protein; protein; Arabidopsis; Bacterial Secretion Systems; Brassica napus; Cells, Cultured; Gene Expression Regulation, Plant; Glucans; Host-Pathogen Interactions; Oomycetes; Plant Diseases; Plants, Genetically Modified; Proteins; Pseudomonas syringae; Recombinant Fusion Proteins
AbstractOomycete pathogens cause diverse plant diseases. To successfully colonize their hosts, they deliver a suite of effector proteins that can attenuate plant defenses. In the oomycete downy mildews, effectors carry a signal peptide and an RxLR motif. Hyaloperonospora arabidopsidis (Hpa) causes downy mildew on the model plant Arabidopsis thaliana (Arabidopsis). We investigated if candidate effectors predicted in the genome sequence of Hpa isolate Emoy2 (HaRxLs) were able to manipulate host defenses in different Arabidopsis accessions. We developed a rapid and sensitive screening method to test HaRxLs by delivering them via the bacterial type-three secretion system (TTSS) of Pseudomonas syringae pv tomato DC3000-LUX (Pst-LUX) and assessing changes in Pst-LUX growth in planta on 12 Arabidopsis accessions. The majority (~70%) of the 64 candidates tested positively contributed to Pst-LUX growth on more than one accession indicating that Hpa virulence likely involves multiple effectors with weak accession-specific effects. Further screening with a Pst mutant (ΔCEL) showed that HaRxLs that allow enhanced Pst-LUX growth usually suppress callose deposition, a hallmark of pathogen-associated molecular pattern (PAMP)-triggered immunity (PTI). We found that HaRxLs are rarely strong avirulence determinants. Although some decreased Pst-LUX growth in particular accessions, none activated macroscopic cell death. Fewer HaRxLs conferred enhanced Pst growth on turnip, a non-host for Hpa, while several reduced it, consistent with the idea that turnip's non-host resistance against Hpa could involve a combination of recognized HaRxLs and ineffective HaRxLs. We verified our results by constitutively expressing in Arabidopsis a sub-set of HaRxLs. Several transgenic lines showed increased susceptibility to Hpa and attenuation of Arabidopsis PTI responses, confirming the HaRxLs' role in Hpa virulence. This study shows TTSS screening system provides a useful tool to test whether candidate effectors from eukaryotic pathogens can suppress/trigger plant defense mechanisms and to rank their effectiveness prior to subsequent mechanistic investigation. © 2011 Fabro et al.
Publication date
LanguageEnglish
AffiliationNational Research Council Canada (NRC-CNRC); NRC Plant Biotechnology Institute (PBI-IBP)
Peer reviewedYes
NPARC number21271278
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Record identifierf390cbb2-2ca3-4d0d-bbc9-a0b2f9c39ef8
Record created2014-03-24
Record modified2016-05-09
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