热激信号转导中的钙-钙调素途径

Ca^(2+)-CaM Pathway of Heat Shock Signal Transduction

大量证据证明钙-钙调素(Ca2+ CaM)信号系统参与植物的热激信号转导。用激光共聚焦扫描显微镜研究小麦胞内Ca2+浓度的变化,37℃热激可引起小麦胞内自由Ca2+浓度的迅速提高。在Ca2+存在条件下,热激也引起小麦CaM基因CaM1-2的表达及细胞内CaM蛋白含量的提高。用CaCl2处理小麦幼苗明显提高小麦热激基因hsp26和hsp70的表达和热激蛋白的合成,而Ca2+的螯合剂EGTA,Ca2+通道阻断剂异博定和LaCl3、CaM抑制剂W7、TFP和CPZ明显降低了热激基因hsp26和hsp70的表达和热激蛋白的合成。EGTA、易博定、TFP或CPZ的处理也阻止小麦耐热性的获得。小麦CaM基因与热激基因的表达动力学研究表明CaM位于热激信号转导的上游,而Ca2+是热激启动的胞内关键因子。凝胶阻滞分析提出Ca2+ CaM在热激信号转导中的作用是通过激活热激转录因子的DNA结合活性来实现的。提出在植物细胞内存在一条新的热激信号转导途径:钙-钙调素途径。

Laboratory studies by the author showed the involvement of calcium and calcium-activated calmodulin (Ca^(2+)-CaM) in heat shock (HS) signal transduction. Using Fluo-3/AM and Laser Scanning Confocal Microscopy, it was found that the increase of intracellular free calcium ion concentration started within 1 min after a 37 ℃ HS in wheat. The levels of CaM mRNA and protein increased during HS at 37 ℃ in the presence of Ca^(2+). The expression of hsp26 and hsp70 genes, synthesis of heat shock proteins were up-regulated by addition of CaCl_2, and down-regulated by the Ca^(2+) chelator EGTA, the Ca^(2+) channel blockers LaCl_3 and verapamil, or the CaM antagonists W7, CPZ and TFP. The acquired thermotolerance developed by HS at 37 ℃ was eliminated by treatment with EGTA, verapamil, CPZ and TFP. The temporal expression of the CaM1-2 gene, and the hsp26 and hsp70 genes, demonstrated that CaM is located upstream in HS signal transduction, and Ca^(2+) is the key factor turning on HS signal transduction pathway. The results obtained by gel mobility shift assay demonstrated that Ca^(2+)-CaM is involved in HS signal transduction by regulating DNA-binding activity of HS transcription factor. Based on above findings, a new pathway, Ca^(2+)-CaM pathway of HS signal transduction, was proposed.