We cloned the gene and a cDNA for a second CTP: phosphorylcholine cytidylyltransferase (CCT, EC 18.104.22.168) annotated in chromosome 4 by the Arabidopsis genome project, and designated the gene AtCCT2 to discriminate it from the isogene AtCCT1 in chromosome 2. When Arabi- dopsis plants were chilled at 2°C for 12 h, the level of AtCCT2 transcripts in the rosettes increased about 6-fold over that before 2°C treatment. By contrast, no significant change occurred in the level of AtCCT1 transcripts during 7 d of 2°C treatment. Immunoblot analysis revealed that the level of AtCCT2 in the rosettes chilled at 2°C increased, and that the level of AtCCT1 showed minor changes, when compared with those before cold treatment. Total CCT activity measured at 2°C increased in plants subjected to 2°C treatment, and this increase was sufficient to account for lipid changes induced by the 2°C treatment. We there- fore concluded that Arabidopsis utilizes two distinct CCT isozymes for CDP-choline synthesis during cold acclima- tion. Our findings are important in understanding the physiological functions of CCT isozymes in Arabidopsis and will also stimulate efforts to understand the physiological significance of phosphatidylcholine at low temperatures.