Department of Chemistry, Seoul National University, South Korea.
Biochem J. 2010 Apr 14;427(3):359-67. doi: 10.1042/BJ20091762.
Changes in membrane fluidity are the earliest cellular events that occur in plant cells upon exposure to cold. This subsequently triggers physiological processes, such as calcium influx and reorganization of actin cytoskeletons, and induces expression of cold-responsive genes. The plasma-membrane-anchored NAC (NAM/ATAF/CUC) transcription factor NTL6 is of particular interest. Cold triggers proteolytic activation of the dormant NTL6 protein, which in turn elicits pathogen-resistance responses by inducing a small group of cold-inducible PR (pathogenesis-related) genes in Arabidopsis. In the present study, we show that proteolytic processing of NTL6 is regulated by cold-induced remodelling of membrane fluidity. NTL6 processing was stimulated rapidly by cold. The protein stability of NTL6 was also enhanced by cold. The effects of cold on NTL6 processing and protein stability were significantly reduced in cold-acclimatized plants, supporting the regulation of NTL6 processing by membrane fluidity. Consistent with this, although NTL6 processing was stimulated by pharmacological agents that reduce membrane fluidity and thus mimic cold, it was inhibited when plants were treated with a 18:3 unsaturated fatty acid, linolenic acid. In addition, the pattern of NTL6 processing was changed in Arabidopsis mutants with altered membrane lipid compositions. Assays employing chemicals that inhibit activities of the proteasome and proteases showed that NTL6 processing occurs via the regulated intramembrane proteolysis mechanism. Interestingly, a metalloprotease inhibitor blocked the NTL6 processing. These observations indicate that a metalloprotease activity is responsible for NTL6 processing in response to cold-induced changes in membrane fluidity.
细胞膜流动性的变化是植物细胞在受到低温胁迫时最早发生的细胞事件。这随后会引发生理过程，如钙离子内流和肌动蛋白细胞骨架的重排，并诱导冷响应基因的表达。质膜锚定的 NAC（NAM/ATAF/CUC）转录因子 NTL6 特别引人注目。低温触发休眠 NTL6 蛋白的蛋白水解激活，进而通过诱导拟南芥中一小群冷诱导的 PR（发病相关）基因来引发抗病反应。在本研究中，我们表明 NTL6 的蛋白水解加工受低温诱导的膜流动性重塑调控。低温能迅速刺激 NTL6 的加工。低温还增强了 NTL6 的蛋白稳定性。在经过低温驯化的植物中，低温对 NTL6 加工和蛋白稳定性的影响显著降低，支持了膜流动性对 NTL6 加工的调控。与之一致的是，尽管 NTL6 的加工受到降低膜流动性并模拟低温的药理学药物的刺激，但当植物用 18:3 不饱和脂肪酸亚麻酸处理时，它被抑制。此外，在膜脂组成改变的拟南芥突变体中，NTL6 的加工模式发生了变化。采用抑制蛋白酶体和蛋白酶活性的化学物质进行的测定表明，NTL6 的加工是通过调节的膜内蛋白水解机制进行的。有趣的是，金属蛋白酶抑制剂阻断了 NTL6 的加工。这些观察结果表明，金属蛋白酶活性负责响应低温诱导的膜流动性变化对 NTL6 的加工。
