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Pathogen-host interactions feature a dynamic interplay between defence signalling cascades and specialized pathogen machineries that can subvert immunity. Plant pathogens secrete effector molecules that enable parasitic infection and reproduction and thus determine the success of the interaction with the host. The Phytophthora species P. capsici, a hemi-biotrophic oomycete, affects a wide range of members of important crop families such as cucurbits and solanaceae worldwide. Despite the presence of diverse effector repertoires, P. capsici shares a number of RXLR proteins with other Phytophthora species in this genus. To better understand the interaction between Phytophthora and its hosts on the molecular level, the infection process of P. capsici was explored on four plant species and compared to phenotypic observations. A model infection system was established to characterise the hemi-biotrophic life-style using a set of three marker genes that determine the three steps during the P. capsici life cycle: biotrophy, necrotrophy and sporulation. Using a unique microarray approach that combined pathogen and tomato genomes on one array, important insights were gained into the transcriptional changes during disease development. While a large number of P. capsici genes were differentially regulated during the biotrophic phase, a number of genes including some RXLR effectors were found to be upregulated only during the necrotrophic phase. Analysis of tomato gene expression identified two distinct transcriptional responses to P. capsici infection. It is hypothesised that conserved effectors play important roles in virulence and form attractive targets to disable pathogenesis. The P. capsici effector Pc03192 was identified as the putative ortholog to the well studied P. infestans Pi03192 that is known to interact with two potato NAC transcription factors. For Pc03192 and the orthologous tomato NACs SlNAC1 and SlNAC2, a yeast-two-hybrid screen could confirm weak protein interaction, and confocal microscopy provided evidence for a co-localisation of the putative interactors to the endoplasmatic reticulum. Results gained in this Thesis open the door towards comparative transcriptomics that should help unravel pathogen infection strategies and exploit host basal defence responses, as well as enable future studies into conserved Phytophthora effector proteins. |
