ECR参与CTR1介导的乙烯信号转导研究

The seedling triple-response phenotype has been used for the analysis of ethylene responses in Arabidopsis and for the isolation of ethylene response mutants. However, it appears that no more new mutant can be isolated based on the seedling triple-response phenotype, probably due to the saturation of genetic screen. Here we report that using a weak ctr1 (Constitutive Triple Response 1) mutant, we were able to isolate mutants that enhance the ctr1 mutant phenotype. The mutants elevate the ctr1-10 mutant phenotype and exhibit severe inhibition in the hypocotyl elongation in etiolated seedlings and the rosette growth are largely inhibited when grown in the air. Ethylene response and genetic analyses for the mutants suggest that the ecr mutants phenotype are dependent on the ctr1-10 mutation. The mutants are new ethylene signal transduction components acting downstream of receptors and upstream of EIN3. Functional analyses of ECR will enrich our understanding of CTR1- involved ethylene signaling transduction in Arabidopsis.

拟南芥白化苗的"三重反应"现象常被用于筛选乙烯反应突变体。但是这一方法筛选得到的突变体已近趋于饱和，很难再用三重反应现象来筛选到新的乙烯信号途径突变体。本研究中，我们通过筛选一个弱的ctr1（Constitutive Triple Response 1）突变体,ctr1-10的增强子，获得了新的乙烯信号途径组分突变体ecr(Enhancer of CTR1)。ECR突变加重了ctr1-10的组成型乙烯反应表型，突变体表现强烈的组成型乙烯反应。遗传分析和银离子处理结果表明ECR作用于受体下游，EIN3上游，负调乙烯反应。ECR的克隆和功能研究将进一步完善我们对CTR1参与的乙烯信号转导机制的认识。

植物激素乙烯气体参与植物各个生长发育过程以及响应外在的刺激。乙烯受体与Raf-like蛋白CONSTITUTIVE TRIPLE RESPONSE1 (CTR1)互作后通过未知机制激活CTR1。激活的CTR1对ETHYLENE INSENSITIVE2 (EIN2) 进行磷酸化，EIN2被磷酸化后驻留在内质网膜，乙烯信号传递被抑制。CTR1功能如何受到调控，需要进一步阐述。ctr1-10突变导致CTR1蛋白水平大幅下降，植株表现减弱的组成性乙烯反应；该突变体有利于我们通过遗传筛选获得参与CTR1功能调控的信号组分。我们发现ENHANCING CTR1-10 ETHYLENE RESPONSE1 (ECR1)功能缺失突变将ctr1-10的突变应表型增强到典型的组成性乙烯反应水平。遗传分析暗示ECR1和CTR1作用于乙烯受体下游，在EIN2与转录因子EIN3/EIL上游。系统分析显示，ECR1与人类抑癌蛋白(HsECR1)高度同源；外源表达HsECR1可以替代拟南芥ECR1的功能。在拟南芥中表达ECR1和HsECR1的 GFP融合蛋白定位于质网；免疫分析也显示ECR1的膜定位特征。这些结果表明HsECR1和ECR1在功能上具有保守性。HsECR1 抑制染色体脆性位点造成的多种肿瘤发生，但是其作用机理并不清楚；ECR1是否与染色体稳定性相关有待进一步研究。ECR1和HsECR1在拟南芥中的功能保守性暗示在植物与人类中抑制乙烯信号和癌变信号的相关组分和机制具有共同的保守性。除了揭示ECR1参与了植物乙烯信号途径，我们的发现对于揭示哺乳动物染色体脆性相关的抑癌蛋白ECR1作用机理具有前瞻意义，同时也表明了乙烯信号负调网络的复杂性。