Function and diversity of oomycetous and fungal small RNAs suppressing host plant immunity

病原菌与寄主植物相互作用的结果在很大程度上取决于植物的免疫强度和病原菌抑制寄主免疫的能力。近年来，我们发现植物病原菌灰葡萄孢（Botrytis cinerea）产生的sRNAs可以劫持植物RNA干扰通路，使重要的植物免疫基因沉默。基于这些知识，本项目的目的是研究宿主免疫抑制rna在独立进化的不同病原体中的发生和性质。我们提出了一个工作流程，旨在利用高通量筛选方法，鉴定由真菌和卵菌界的代表性植物病原体产生的新病原体sRNAs，即引起拟南芥白粉病的goovinomyces orontii，引起拟南芥霜霉病的Hyaloperonospora Arabidopsis，以及引起番茄和马铃薯晚疫病的Phytophthora infestans。通过植物mRNA降解分析来缩小候选sRNAs的范围。主要的重点将放在具有高潜力的与植物应激反应和免疫相关的宿主基因的候选基因上。候选宿主靶基因的真正沉默将通过植物病原体sRNA的表达来证明。此外，沉默宿主靶基因在防御和宿主免疫中的功能作用将被表征。最后，我们将应用分析和随机进化模型来解决植物基因、基因家族和病原体sRNAs靶向的分子途径之间是否存在趋同模式。此外，我们的目标是在病原体和宿主之间的共同进化军备竞赛中检测病原体sRNAs靶向的宿主基因中的正选择特征。因此，该项目旨在回答以下基本问题。I)不同的丝状植物病原体是否利用sRNAs抑制宿主免疫？II)靶向宿主基因和途径在宿主免疫中的作用是什么？不同病原体产生的sRNAs是否表现出靶基因趋同？IV)病原体sRNAs靶向的宿主基因和途径中是否存在正选择的特征？

The outcome of the interaction between a pathogen and a host plant largely relies on the immune strength of the plant and on the ability of the pathogen to suppress host immunity. We discovered recently that the plant pathogen Botrytis cinerea produces sRNAs that hijack the plant RNA interference pathway and silence important plant immunity genes. Based on this knowledge, the aim of this project is to investigate the occurrence and nature of host immune-suppressive sRNAs in distinct pathogens that evolved independently. We propose a workflow that aims at identifying novel pathogen sRNAs produced by representative plant pathogens of the fungus and oomycete kingdoms, namely Golovinomyces orontii causing the powdery mildew disease in Arabidopsis, Hyaloperonospora arabidopsidis causing the downy mildew disease in Arabidopsis, and Phytophthora infestans causing the late blight disease in tomato and potato, using high throughput screening approaches. Candidate sRNAs will be narrowed down through plant mRNA degradome analysis. The primary focus will be on candidates with high potential to target host genes related to plant stress response and immunity. Proof of bona-fide silencing of candidate host target genes will be performed by in planta pathogen sRNA expression. Moreover, the functional role of the silenced host target genes in defence and host immunity will be characterized. Finally, we will apply analytical and stochastic evolutionary models to address whether convergent patterns exist among plant genes, gene families, and molecular pathways targeted by pathogen sRNAs. Additionally, we aim to detect signatures of positive selection within host genes targeted by pathogen sRNAs with respect to the co-evolutionary arms race between pathogens and their hosts. This project is therefore designed to answer the following fundamental questions. I) Do distinct filamentous plant pathogens utilize sRNAs to suppress host immunity? II) What are the roles of targeted host genes and pathways in host immunity? III) Do sRNAs produced by distinct pathogens show target gene convergence? IV) Are there signatures of positive selection in host genes and pathways targeted by pathogen sRNAs?