Multiple Candidate Effectors from the Oomycete Pathogen Hyaloperonospora arabidopsidis Suppress Host Plant Immunity

PLoS Pathogens

Rebecca L. Allen¹  Alejandra Rougon-Cardoso²  Marie-Cecile Caillaud³  Guido Van den Ackerveken⁴  Laura Baxter⁵  Mary Coates⁵  Jens Steinbrenner⁵  David Greenshields⁵  Evelyn Körner⁶  Jane E. Parker⁶  Jonathan D. G. Jones⁶  Naveed Ishaque⁶  Georgina Fabro⁶  Kee-Hoon Sohn⁶  Sophie J. M. Piquerez⁶  Jim Beynon⁶  Rita Lei⁶  Jorge L. Badel⁶  David J. Studholme⁷ 

[1] Biosciences, College of Life and Environmental Sciences, University of Exeter, Exeter, United Kingdom;John Innes Centre, Norwich, United Kingdom;Laboratorio Nacional de Genomica para la Biodiversidad, CINVESTAV Irapuato, Mexico;National Research Council Canada, Plant Biotechnology Institute, Saskatoon, Canada;School of Life Sciences, Warwick University, Wellesbourne, United Kingdom;The Sainsbury Laboratory, John Innes Centre, Norwich, United Kingdom;Warwick Systems Biology, Warwick University, Coventry, United Kingdom

关键词: Arabidopsis thaliana;    Leaves;    Genetically modified plants;    Bioluminescence;    Plant genomics;    Sequence motif analysis;    Bacterial growth;    Cloning;   

DOI  :  10.1371/journal.ppat.1002348

学科分类：生物科学（综合）

来源: Public Library of Science

【 摘 要 】

Oomycete 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.

【 授权许可】

CC BY