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Crop diseases cause economic losses amounting to over $200 billion each year. One of the most devastating crop failures was caused by the oomycete pathogen Phytophthora infestans that led to the Irish Potato Famine in the 1840s. The oomycete Hyaloperonospora arabidopsidis (Hpa) is a useful pathogen to study oomycete Hyaloperonospora arabidopsidis (Hpa) is a useful pathogen to study oomycete diseases as it is a natural pathogen of the model plant Arabidopsis and a draft genome sequence of the Hpa race Emoy2 is available. Three approaches have been used in this study to identify host and pathogen genes involved in the interaction between Arabidopsis and Hpa. A cDNA library of Hpa race Noco2 transcripts expressed in plant a was generated.

In order to identify potential avirulence factors of <i>Phytophthora infestans</i>, secreted protein profiles of six strains (IPO-0, CBS431.90, IPO-655-2A, IPO-428-2, 88069 and 90128) with different avirulence phenotypes were analysed by proteomics.  The proteins from culture filtrates were visualised on 2D gels with a total number between 350 and 1000.  PiAVR X was found only in avirulent strains and considered therefore as a possible avirulence determinant.  Its expression increased in all strains tested when grown in Modified Henniger medium.  Single nucleotide polymorphisms (SNPs) were detected within a 735 nt fragment of <i>PiAvrX</i> but none was linked to avirulence characteristics.  The consensus EST database facilitated identification of approximately 50% of 45 most abundant proteins excised from strain 88069.  Beta-glucosidase, Pi-NIP2 (<i>Phytophthora infestans</i> necrosis inducing protein-like protein), enoyl CoA hydratase, glutathione S transferase, peptidylprolyl isomerase, acidic chitinase and Pi-PR1 (<i>Phytophthora infestans </i>homologue of plant PR-1 protein) were among the identified proteins with a recognisable signal sequence.  Enolase, quinine-oxido reductase, nucleoside di-phosphate kinase, actin depolymerisation factor, thioredoxin, ubiquitin and 14-3-3 protein were also identified but without a signal peptide.  The occurrence and expression of <i>Pi-nip2, Pi-chi1 </i>and <i>Pi-pr1</i> were confirmed in the strains tested.  Transformants were obtained from <i>P. infestans</i> strain T30-4 via a biolistic particle delivery approach using a single plasmid vector containing <i>Pi-pr1</i>.  Detailed analysis of these transformants did not demonstrate induction of homology-dependent gene silencing.  It was found that transformation rates were different among the tested <i>P. infestans</i> strains.