Pieter M. J. A. van Poppel,1,2
Peter J. I. van de Vondervoort,1
Maartje W. M. Jung,1
Paul R. J. Birch,4
Stephen C. Whisson,4 and
1Laboratory of Phytopathology, Wageningen University, Binnenhaven 5, 6709 PD Wageningen and Graduate School Experimental Plant Sciences, The Netherlands; 2Centre for BioSystems Genomics (CBSG), P.O. Box 98 6700 AB Wageningen, The Netherlands; 3Institute of Vegetables and Flowers, Chinese Academy of Agricultural Sciences, Beijing 100081 and College of Plant Protection, Northwest A & F University, Yangling Shaanxi 712100, China; 4Plant-Pathology Programme, Scottish Crop Research Institute, Invergowrie, Dundee DD2 5DA, Scotland, U.K.
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Accepted 30 June 2008.
Resistance in potato against the oomycete Phytophthora infestans is conditioned by resistance (R) genes that are introgressed from wild Solanum spp. into cultivated potato. According to the gene-for-gene model, proteins encoded by R genes recognize race-specific effectors resulting in a hypersensitive response (HR). We isolated P. infestans avirulence gene PiAvr4 using a combined approach of genetic mapping, transcriptional profiling, and bacterial artificial chromosome marker landing. PiAvr4 encodes a 287-amino-acid-protein that belongs to a superfamily of effectors sharing the putative host-cell-targeting motif RXLR-dEER. Transformation of P. infestans race 4 strains with PiAvr4 resulted in transformants that were avirulent on R4 potato plants, demonstrating that PiAvr4 is responsible for eliciting R4-mediated resistance. Moreover, expression of PiAvr4 in R4 plants using PVX agroinfection and agroinfiltration showed that PiAvr4 itself is the effector that elicits HR on R4 but not r0 plants. The presence of the RXLR-dEER motif suggested intracellular recognition of PiAvr4. This was confirmed in agroinfiltration assays but not with PVX agroinfection. Because there was always recognition of PiAvr4 retaining the signal peptide, extracellular recognition cannot be excluded. Deletion of the RXLR-dEER domain neither stimulated nor prevented elicitor activity of PiAvr4. Race 4 strains have frame shift mutations in PiAvr4 that result in truncated peptides; hence, PiAvr4 is apparently not crucial for virulence.
Additional keywords:late blight, plant pathogen, RXLR motif.
© 2008 The American Phytopathological Society