Functional characterisation of a novel semi-dominant mutant allele of the "Chitin Elicitor Receptor-like Kinase" CERK1

本项目的重点是一个新的分子机制，控制细胞死亡执行和遏制在植物细胞响应病原体感染。我们之前已经在拟南芥的CERK1基因（CERK1 -4）中发现了一种新的半显性突变，该突变增强了对几种生物营养白粉病真菌感染的抵抗力。值得注意的是，这种耐药性与失控的扩散性细胞死亡反应相关。这表明，质膜定位受体样激酶CERK1除了在真菌PAMP几质（以及尚未确定的细菌危险信号）的感知中起作用外，还是病原体诱导的细胞死亡的调节剂。有趣的是，内在激酶活性并不需要cerk1-4突变表型。相反，我们已经证明，CERK1 -4突变体中的异常细胞死亡遏制与CERK1蛋白可溶性33 kDa衍生物的缺乏相关，该衍生物代表n端外结构域。在野生型植物中，这个外结构域片段定位于外质体，似乎是受控酶解蛋白的产物。在脊椎动物中，严格调节跨膜蛋白外结构域的脱落是一种完善的翻译后调节机制。据我们所知，植物蛋白的外结构域脱落尚未被描述。因此，cerk1-4突变等位基因为了解植物跨膜蛋白的外结构域脱落以及这种调节机制如何参与植物细胞死亡遏制提供了一个很好的切入点。

This project focuses on a novel molecular mechanism that controls cell death execution and containment in plant cells in response to pathogen infection. We have previously identified a novel semi-dominant mutation in the CERK1 gene of Arabidopsis (cerk1-4), which confers enhanced resistance to infection by several biotrophic powdery mildew fungi. Significantly, this resistance is correlated with a deregulated spreading cell death response. This indicates that the plasma-membrane localised receptor-like kinase CERK1, apart from its function in the perception of the fungal PAMP chitin (and a yet unidentified bacterial danger signal) is a regulator of pathogen-induced cell death. Interestingly, intrinsic kinase activity is not required for the cerk1-4 mutant phenotype. Instead, we have shown that aberrant cell death containment in the cerk1-4 mutant correlates with lack of a soluble 33 kDa derivative of the CERK1 protein, which represents the N-terminal ectodomain. In wild-type plants, this ectodomain fragment localises to the apoplast and appears to be the product of controlled enzymatic proteolysis. In vertebrates, tightly regulated shedding of the ectodomain of trans-membrane proteins is a well-established post-translational regulatory mechanism. To our knowledge, ectodomain shedding has not yet been described for plant proteins. The cerk1-4 mutant allele thus represents an excellent entree into understanding ectodomain shedding of plant transmembrane proteins in general and how this regulatory mechanism is involved in plant cell death containment.