Proteomics and phosphoproteomics of P. infestans and potato

We are using proteomics to study the underlying processes that govern pathogenicity and development in Phytophthora infestans and resistance to P. infestans in potato. In a large-scale phosphoproteomics study of six life stages, we obtained quantitative data for 2922 phosphopeptides. Life stage-specific phosphopeptides include ABC transporters and an appressorium specific kinase. We also identified 2179 phosphorylation sites and deduced 22 phosphomotifs. In addition, we detected tyrosine phosphopeptides that are potential targets of tyrosine kinases. Among the phosphorylated proteins are members of the RXLR and Crinkler effector families. The latter are phosphorylated in several life stages, in sites that are conserved between different members of the Crinkler family. This indicates that proteins in the Crinkler family have functions beyond their putative role as (necrosis-inducing) effectors. In a proteomic study of the same life stages, we have identified a number of proteins with expression patterns that are specific for life stages involved in (pre) infection. Among these are both proteins previously identified as being specifically expressed in these stages, as well as transport proteins, RXLR proteins, kinases and proteins putatively involved in cell wall synthesis. We are now analysing a selection of these proteins further. In addition, we have also used proteomics to study the apoplastic proteome of potato cultivars with different degrees of resistance to P. infestans in response to infection, identifying potential effector targets and proteins involved in pathogen resistance. Thus, we show that proteomic techniques are valuable tools to elucidate novel mechanisms of pathogenicity and resistance in oomycete-host interactions.