Borhan M Hossein, Gunn Nick, Cooper Abigail, Gulden Sigrun, Tör Mahmut, Rimmer S Roger, Holub Eric B
Agriculture and Agri-Food Canada, Saskatoon Research Centre, Saskatoon, SK., S7N 0X2, Canada.
Mol Plant Microbe Interact. 2008 Jun;21(6):757-68. doi: 10.1094/MPMI-21-6-0757.
White blister rust in the Brassicaceae is emerging as a superb model for exploring how plant biodiversity has channeled speciation of biotrophic parasites. The causal agents of white rust across a wide breadth of cruciferous hosts currently are named as variants of a single oomycete species, Albugo candida. The most notable examples include a major group of physiological races that each are economically destructive in a different vegetable or oilseed crop of Brassica juncea (A. candida race 2), B. rapa (race 7), or B. oleracea (race 9); or parasitic on wild crucifers such as Capsella bursa-pastoris (race 4). Arabidopsis thaliana is innately immune to these races of A. candida under natural conditions; however, it commonly hosts its own molecularly distinct subspecies of A. candida (A. candida subsp. arabidopsis). In the laboratory, we have identified several accessions of Arabidopsis thaliana (e.g.,. Ws-3) that can permit varying degrees of rust development following inoculation with A. candida races 2, 4, and 7, whereas race 9 is universally incompatible in Arabidopsis thaliana and nonrusting resistance is the most prevalent outcome of interactions with the other races. Subtle variation in resistance phenotypes is evident, observed initially with an isolate of A. candida race 4, indicating additional genetic variation. Therefore, we used the race 4 isolate for map-based cloning of the first of many expected white rust resistance (WRR) genes. This gene was designated WRR4 and encodes a cytoplasmic toll-interleukin receptor-like nucleotide-binding leucine-rich repeat receptor-like protein that confers a dominant, broad-spectrum white rust resistance in the Arabidopsis thaliana accession Columbia to representative isolates of A. candida races 2, 4, 7, and 9, as verified by transgenic expression of the Columbia allele in Ws-3. The WRR4 protein requires functional expression of the lipase-like protein EDS1 but not the paralogous protein PAD4, and confers full immunity that masks an underlying nonhypersensitive incompatibility in Columbia to A. candida race 4. This residual incompatibility is independent of functional EDS1.
十字花科植物中的白锈病正逐渐成为探索植物生物多样性如何引导活体营养型寄生虫物种形成的绝佳模型。目前，广泛分布于十字花科寄主植物上的白锈病致病因子被命名为单一卵菌物种——白锈菌（Albugo candida）的变种。最显著的例子包括一大类生理小种，其中每个小种都会对不同的蔬菜或油菜作物造成经济损失，例如对芥菜（白锈菌小种2）、白菜（小种7）或甘蓝（小种9）；或者寄生于野生十字花科植物，如荠菜（小种4）。在自然条件下，拟南芥对这些白锈菌小种具有天然免疫力；然而，它通常会寄生其自身分子上不同的白锈菌亚种（白锈菌拟南芥亚种）。在实验室中，我们鉴定出了几个拟南芥品系（例如Ws-3），在用白锈菌小种2、4和7接种后，这些品系能允许不同程度的锈病发展，而小种9在拟南芥中普遍不亲和，与其他小种相互作用时最常见的结果是不产生锈病抗性。抗性表型存在细微差异，最初在用白锈菌小种4的一个分离株观察时就很明显，这表明存在额外的遗传变异。因此，我们使用小种4分离株对众多预期的白锈病抗性（WRR）基因中的第一个进行图位克隆。该基因被命名为WRR4，编码一种细胞质Toll样白细胞介素受体样核苷酸结合富含亮氨酸重复序列的受体样蛋白，通过在Ws-3中对哥伦比亚等位基因进行转基因表达验证，该蛋白在拟南芥哥伦比亚品系中对代表性的白锈菌小种2、4、7和9赋予显性、广谱的白锈病抗性。WRR4蛋白需要脂酶样蛋白EDS1的功能性表达，但不需要同源蛋白PAD4，并且赋予完全免疫性，掩盖了哥伦比亚品系对白锈菌小种4潜在的非过敏不亲和性。这种残留的不亲和性独立于功能性EDS1。
