Molecular mechanisms of pathogen adaptation to plant defenses

植物病害是加拿大和全世界所有经济作物的一个制约因素。抗病品种的开发和应用是公共和私营部门的一项经常性工作，但这些品种的可持续性经常面临挑战。在缺乏抗性品系的情况下，种植者使用栽培实践和化学品来减轻疾病的负面影响。然而，只有采取综合和可持续的疾病管理战略，才能取得令人满意的结果。建立这种方法比以往任何时候都更需要更好地理解每种所考虑的疾病中的宿主-病原体相互作用，即，病原体感染/定殖植物的能力和植物对这种攻击的反应。我的研究项目侧重于这两个方面的机制，但更多的是了解病原体如何处理宿主防御，以及在某些情况下，它们如何操纵宿主的新陈代谢以达到自己的优势。利用消减杂交/cDNA-AFLP技术，我们鉴定了几个参与马铃薯-大丽轮枝菌和马铃薯-晚疫病菌互作的差异表达基因和蛋白。这些基因包括控制这些病原体的致病性或无毒性的基因，以及其他可能与植物对这些病原体的抗性或易感性有关的基因。我们克隆并测序了几个差异表达的转录衍生片段。我们选择了一组相应的基因，并对其进行了功能表征，以确定它们在发病机制或防御中的作用。追踪单个基因或蛋白质可以提供关于其功能作用的信息，并且可以在基因对基因的相互作用中具有很大的价值，例如其用于植物抗病性。在多基因抗性的情况下，一个看似重要的基因的价值和用途成为一个移动的目标，因为病原体使用适应性策略来平衡其需求并应对新的情况。在这种情况下，我的目标是理解一个考虑到这种复杂性的集成系统中的每个交互。我的目标是：（i）完成我们认为在植物-大丽轮枝菌相互作用中重要的基因的功能研究，（ii）对相互作用的每个片段进行细胞和器官表达定位（对根分泌物的反应、感染、定殖和症状发展），沿着每个节段的信号传导机制，以及（iv）理解允许病原体随时间适应的发病机理变化的机制。将这些发现整合到致病基因分布模型中，最终将导致预测植物和病原体对来自其对应物和环境的线索的反应。确定这些要素和过程将是有效减轻植物病害负面影响的又一步。

Plant diseases represent a constraint for all economic crops in Canada and worldwide. The development and deployment of disease resistant varieties is a constant exercise in both public and private sectors, but the sustainability of such varieties frequently faces challenges. In absence of resistant lines, growers use cultural practices and chemicals to mitigate the negative impact of diseases. However, satisfactory results can only be achieved with integrated and sustainable disease management strategies. More than ever, establishing such approaches requires better understanding of host-pathogen interactions in each considered disease, i.e., pathogens' ability to infect/colonize plants and plants' responses to such attacks. My research program focuses on the mechanisms of both aspects, but more on understanding how pathogens handle host defenses and, in cases, how they manipulate the host's metabolism to their own advantage. Using subtractive hybridization/cDNA-AFLP, we identified several differentially expressed genes and proteins involved in the potato-V. dahliae and potato-P. infestans interactions. These included genes controlling pathogenesis or avirulence in these pathogens, as well as others potentially involved in plant resistance or susceptibility to these pathogens. We cloned and sequenced several differentially expressed transcript-derived fragments. We selected a set of corresponding genes and have been functionally characterizing them to determine their role either in pathogenesis or defense. Chasing a single gene or protein may provide information on its functional role and can be of great value in a gene-for-gene interaction, for example its deployment for plant disease resistance. In the case of polygenic resistance, the value and use of one seemingly important gene becomes a moving target as the pathogen uses adaptive strategies to balance its needs and respond to new situations. In this context, my goal is to understand each interaction in an integrated system that takes this complexity under account. My objectives for the term of this proposal are to (i) complete functional studies of genes we deemed important in plant-V. dahliae interaction, (ii) run cell and organ localization of their expression for each segment of the interaction (Response to root exudates, Infection, Colonization, and Symptom development), along with the signaling mechanisms accompanying each segment, and (iv) understanding the mechanisms of pathogenesis variations that allow pathogen adaptation over time. Integrating these findings into a pathogenesis gene distribution model will eventually lead to predicting plant and pathogen responses to clues from their counterpart and the environment. Identifying these elements and processes will be one step further towards efficiently mitigating the negative impacts of plant diseases.