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

本项目的重点是一种新的分子机制，它控制细胞死亡、执行和遏制植物细胞对病原体侵染的反应。我们以前已经在拟南芥的CERK1基因(cerk1-4)中发现了一个新的半显性突变，该突变增强了对几种生物营养白粉菌的侵染。值得注意的是，这种抗性与非调控的扩散细胞死亡反应相关。这表明，质膜上定位的受体样激酶CERK1除了在感知真菌PAMP几丁质(以及一个尚未识别的细菌危险信号)中的功能外，还是病原体诱导的细胞死亡的调节因子。有趣的是，cerk1-4突变表型不需要内在的激酶活性。相反，我们已经证明了cerk1-4突变体中异常的细胞死亡遏制与缺乏代表N端胞外结构域的CERK1蛋白的33 kDa可溶衍生物有关。在野生型植物中，这种胞外结构域片段定位于质外体，似乎是受控的酶蛋白分解的产物。在脊椎动物中，严格调控跨膜蛋白胞外区的脱落是一种成熟的翻译后调节机制。据我们所知，目前还没有关于植物蛋白胞外结构域脱落的描述。因此，cerk1-4突变等位基因是了解植物跨膜蛋白胞外区脱落以及这一调控机制如何参与植物细胞死亡遏制的极佳途径。

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.