Deciphering the molecular basis of organ-specificity in plant-microbe interactions

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Coevolution between plants and pathogens has culminated in intricate patterns where pathogens can have a narrow or wide host range. This evolutionary paradigm of host specialization also holds true for organ-specific infection processes. However, it remains elusive why some pathogens prefer a given organ, whereas others are able to infect the entire plant. Studies have shown that distinct plant organs may utilize distinct defense mechanisms, but not much is known about pathogens' molecular determinants involved in organ-specificity.***Because of its broad ability to colonize different host organs, the*potato late blight pathogen Phytophthora infestans is a perfect model to*tackle organ-specificity. Moreover, while late blight resistance*breeding has often focused on foliage, tuber resistance is an equally*important trait since tuber infection can result in severe yield*reduction and promotes colonization by secondary soft-rotting bacteria.*Some late blight resistance genes have been shown to be ineffective in*tubers, which could be explained by the absence of expression of the*corresponding avirulence genes in these tissues. ***This proposal aims at identifying whether distinct effector complements act in various plant organs, and to decipher their contribution in dictating organ-specificity. Candidate organ-specific virulence factors will be identified by transcriptome profiling of effector-encoding genes across various organs and validated using functional assays. Organ-specific effectors are expected to possess a significantly higher expression level in a given organ relative to other organs and their virulence function (e.g. ability to suppress defense responses) should act in an organ-specific manner. In parallel, known avirulence factors will also be tested for their ability to trigger defense responses in various organs from genetically-resistant potato cultivars.***From a fundamental point of view, the elucidation of organ-specific constraints is a neglected component of plant-microbe interactions that is crucial to our understanding of both evolutionary and ecological aspects of such interactions. Besides, by implementing novel knowledge on organ-specific vs. whole plant virulence and resistance mechanisms, this research program will have practical implications for the development of novel strategies for disease control in agricultural crops. This would represent an unprecedented opportunity to translate fundamental research into a crop improvement strategy that would benefit the Canadian industry. **