Phytophthora infestans causes the re-emerging and devastating late blight disease, which threatens potato and tomato production worldwide. With the recent publication of the P. infestans genome, it has become clear that this hemibiotrophic pathogen secretes hundreds of effector proteins to modulate plant immunity and enable colonization. Therefore, my long-term aim is to reveal the mode of action of P. infestans effectors and to analyze host molecular mechanisms that are perturbed by this devastating pathogen. Thereby, I plan to generate valuable information for the scientific community that will help to develop novel strategies to fight against plant pathogens and contribute to addressing the issue of food security. Plant innate immunity relies on pattern recognition receptors that recognize pathogen associated molecular patterns (PAMPs) such as chitin. Given that oomycetes contain some chitin in their cell wall, we decided to investigate the role of chitin recognition in plant immunity against oomycetes. The overall objective of this proposal is to elucidate the mechanism of suppression of chitin elicitor signalling by P. infestans RXLR effector AVRblb2, and to identify host components involved in this process. The rationale behind this research is based on our exciting preliminary data, which showed that (i) silencing of Cerk1 in Nicotiana benthamiana increased susceptibility towards P. infestans infection, (ii) AVRblb2 suppressed the defense responses induced by chitin, and (iii) heterologous expression of AVRblb2 in N. benthamiana increased susceptibility towards P. infestans infection. We aim to determine the extent of suppression of PAMP triggered immunity (PTI) by AVRblb2 and identify the potential mechanism of suppression. We will use a multifaceted approach including genetic, biochemical, and cell imaging methods to functionally characterize suppression of PTI by AVRblb2 and elucidate the role of chitin recognition in plant immunity against P. infestans.