Unveiling effector-triggered immunity by Plasmodiophora brassicae as a source of durable clubroot disease resistance

油菜籽产业和十字花科蔬菜的生产在加拿大和世界各地都有一个共同的敌人：十字花科植物的根瘤病原菌--油菜原虫。Brassicae是一种胞内原生生物，在全球范围内造成数百万人的损失。在过去的10年里，油菜籽根瘤病仅给油菜籽行业造成了约5亿美元的损失。利用抗病品种是避免病原菌危害的关键策略。多年来，抗药性已被新的甘蓝型油菜病原菌迅速克服，突显了确定持久抗药性来源的必要性。在侵染过程中，许多植物病原菌，如油菜疫霉，会释放效应蛋白，抑制植物免疫，促进疾病发展。作为回报，植物进化出了被称为效应器触发免疫(ETI)的防御机制。这一免疫层通过具有核苷酸结合的富含亮氨酸重复序列(NLR)结构域的细胞内受体，在保护特定植物基因型免受特定病原菌小种的侵袭中发挥关键作用，NLR结构域识别病原体效应器。在病原菌菌株中保守的效应器，被称为核心效应器，已被用作探针来筛选新的NLR，以整合到育种计划中，以产生抗性植株。最近，已经报道了不同亚型的油菜疫霉效应器，但到目前为止，油菜疫霉核心效应器还没有确定。我们计划利用它们的基因组序列，在世界范围内识别的不同致病类型中确定甘蓝假单胞菌的核心效应因子。我们进一步计划确定它们的功能，以利用拟南芥-P来诱导ETI(即，ETI诱导的效应器)。Brassicae病理系统模型。为了揭示甘蓝疫霉的这一机制，我们试图实现以下目标：1)根据致病类型和蛋白质家族结构的保守度来表征甘蓝疫霉的核心效应；2)鉴定与甘蓝疫霉NLRs相互作用的甘蓝疫霉效应器；3)鉴定与甘蓝疫霉效应器相关的A.thaliana NLRs；以及4)确定那些介导与甘蓝疫霉效应器相互作用的A.thaliana NLRs是否也存在于其他油菜作物中。这些目标的实现将为了解甘蓝根结线虫生物学和根瘤病病原菌在敏感寄主上建立感染机制提供原创性贡献。从长远来看，这将导致培育出对甘蓝型油菜根腐病具有抗性的植物，并以一种环境友好、成本更低的方式来管理这种根瘤病。

Canola industry and the production of cruciferous vegetables in Canada and worldwide has a common enemy: Plasmodiophora brassicae, the clubroot pathogen of the crucifers. P. brassicae is an intracellular protist responsible for millions in losses worldwide. In the last 10 years, clubroot has cost to the canola industry only, around $500 million in losses. The use of resistant varieties has been a key strategy to avoid the damages caused by the pathogen. Over the years, the resistance has been rapidly overcome by new pathotypes of P. brassicae highlighting the need to identify durable sources of resistance. During the infection process, many plant pathogens such as P. brassicae release effector proteins that can suppress plant immunity and allow disease progression. In return, plants have evolved defense mechanisms known as effector-triggered immunity (ETI). This layer of immunity plays a key role in protecting specific plant genotypes against specific pathogen races through intracellular receptors that possess nucleotide-binding leucine-rich repeat (NLR) domains, which recognize pathogen effectors. Effectors conserved among pathogen strains, termed core effectors, have been used as probes to screen for new NLRs to incorporate into breeding programs to generate resistant plants. Recently, different subsets of P. brassicae effectors have been reported, but to date P. brassicae core effectors have yet to be identified. We plan to define P. brassicae core effectors among the different pathotypes identified worldwide using their genomic sequences. We further plan to determine their functionality to elicit ETI (i.e., ETI-eliciting effectors) using the Arabidopsis thaliana-P. brassicae pathosystem model. To unveil this mechanism for P. brassicae, we seek to fulfill the following objectives: 1) to characterize P. brassicae core effectors in terms of degree of conservation among pathotypes and structure of protein families; 2) to identify P. brassicae effectors interacting with A. thaliana NLRs; 3) to identify A. thaliana NLRs associated with P. brassicae effectors; and 4) to determine if those A. thaliana NLRs mediating the interaction with P. brassicae effectors are also present in other Brassica crops. Achieving these objectives will provide original contributions to the understanding of P. brassicae biology and the mechanisms used by the clubroot pathogen to establish infection in the susceptible host. In the longer term, this will lead to the development of plants resistant to P. brassicae and to an environmentally friendly and less costly management of the clubroot disease.