A functional genomics approach to address the molecular evolutionary concept of pathogen host range and non-host resistance

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A major branch of the plant innate immune system in response to invading pathogens relies on the perception of invariant microbial structures, commonly termed Microbial- or Pathogen-Associated Molecular Patterns (MAMPs/PAMPs) by pattern recognition receptors (PRRs), followed by the activation of a generic anti-microbial response. This process, collectively termed MAMP/PAMP-triggered immunity (MTI/PTI), protects plants against the majority of pathogens and reflects basal or non-host resistance. Successful pathogens have evolved effectors that manipulate or suppress MTI. The molecular evolutionary concept connecting host adaptation, host range and non-host resistance stipulates that a failure to suppress MTI may be due to the lack of effectors capable to interfere efficiently with MAMP signalling, most likely because they are unable to interact with and properly manipulate host target proteins. However, there are very little experimental evidence supporting or infirming this concept.The oomycete genus Phytophthora is an excellent model to address these questions. It contains taxonomically closely-related species but displaying different host range specificities. The general objective of this project will consist to perform a comparative functional study of MTI-suppressing RXLR effectors originated from different Phytophthora spp. in host and non-host plant species. The investigation of pathogen speciation, host adaptation and the phenomenon of non-host resistance at the molecular level will offer insights into the plasticity of oomycete genomes, shedding light on the evolutionary conservation or diversification of RXLR effectors, driven by host-imposed positive selection. This approach will be instrumental to rationalize and to model pathogen co-evolution with hosts that are either closely (host range expansion) or distantly (host jump) related to the present hosts.