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

植物和病原体之间的共同进化已经达到了复杂的模式，其中病原体可以具有狭窄或广泛的宿主范围。这种宿主专门化的进化模式也适用于器官特异性感染过程。然而，为什么一些病原体更喜欢特定的器官，而另一些病原体能够感染整个植物，这仍然是难以捉摸的。研究表明，不同的植物器官可能利用不同的防御机制，但对病原体参与器官特异性的分子决定因素知之甚少。马铃薯晚疫病病原菌疫霉（Phytophthora infestans）具有广泛的定殖能力，是解决器官特异性问题的完美模型。此外，虽然抗晚疫病育种通常集中在叶片上，但抗块茎也是一个同样重要的性状，因为块茎感染会导致产量严重下降，并促进次生软腐细菌的定植。一些抗晚疫病基因在块茎中被证明是无效的，这可以解释为在这些组织中缺乏相应的无毒基因的表达。***本提案旨在确定不同的效应补体是否在不同的植物器官中起作用，并破译它们在决定器官特异性方面的贡献。候选器官特异性毒力因子将通过对不同器官的效应编码基因的转录组分析来鉴定，并使用功能分析进行验证。与其他器官相比，器官特异性效应物在特定器官中的表达水平要高得多，而且它们的毒力功能（如抑制防御反应的能力）应该以器官特异性的方式起作用。与此同时，已知的无毒因子也将测试它们在基因抗性马铃薯品种的各种器官中引发防御反应的能力。***从基本观点来看，阐明器官特异性约束是植物-微生物相互作用中一个被忽视的组成部分，而这对我们理解这种相互作用的进化和生态方面至关重要。此外，通过对器官特异性与整个植物的毒力和抗性机制的新认识，该研究项目将对农业作物疾病控制新策略的发展具有实际意义。这将是一个前所未有的机会，将基础研究转化为有利于加拿大工业的作物改良战略。**

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. **