Inatsugi Rie, Kawai Hiromitsu, Yamaoka Yasuyo, Yu Yanbo, Sekiguchi Akira, Nakamura Masanobu, Nishida Ikuo
Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033, Japan.
Plant Cell Physiol. 2009 Oct;50(10):1727-35. doi: 10.1093/pcp/pcp115. Epub 2009 Aug 10.
Arabidopsis thaliana increases cellular phosphatidylcholine (PC) content during cold acclimation by up-regulating PC biosynthesis. The A. thaliana genes CCT1 and CCT2 encode CTP:phosphorylcholine cytidylyltransferases (CCTs; EC 2.7.7.15), which regulate PC biosynthesis via the CDP-choline pathway. We isolated the T-DNA-tagged knockout mutants cct1 and cct2 of A. thaliana (Wassilevskaja; WS). CCT activity in cct1 and cct2 plants accounted for 29 and 79% to the cellular CCT activity of WS plants, respectively. When plants were exposed to 2 degrees C for 7 d, CCT activity increased in both cct1 and cct2 plants, and immunoblot analyses revealed that cct1 contained an increased level of CCT2 protein whereas cct2 exhibited little increase in CCT1 level. For each mutant grown at 23 degrees C, CCT activity was mainly enriched in the particulate (15,000 x g pellet) and microsomal (150,000 x g pellet) fractions from rosette leaf homogenates. After exposure to cold, the particulate and microsomal fractions of cct1 plants had higher total CCT activity due to increased levels of CCT2; in contrast, the levels of CCT1 in cct2 plants remained unchanged in particulate and microsomal fractions despite a significant increase in the total CCT activity. We conclude that the CDP-choline pathway of A. thaliana is up-regulated at low temperature via isogene-specific modes: enhanced expression of CCT2 and post-translational activation/inactivation of CCT1 in membranes. PC levels were similarly maintained in both mutants and WS plants after 14 d at 2 degrees C, suggesting that either of the CCT genes is sufficient for PC biosynthesis at low temperature.
拟南芥在冷驯化过程中通过上调磷脂酰胆碱（PC）生物合成来增加细胞内PC含量。拟南芥基因CCT1和CCT2编码CTP：磷酸胆碱胞苷转移酶（CCTs；EC 2.7.7.15），它们通过CDP-胆碱途径调节PC生物合成。我们分离了拟南芥（Wassilevskaja；WS）的T-DNA标签敲除突变体cct1和cct2。cct1和cct2植株中的CCT活性分别占WS植株细胞CCT活性的29%和79%。当植株在2℃下暴露7天时，cct1和cct2植株中的CCT活性均增加，免疫印迹分析表明cct1中CCT2蛋白水平升高，而cct2中CCT1水平几乎没有增加。对于在23℃下生长的每个突变体，CCT活性主要富集在莲座叶匀浆的颗粒（15,000×g沉淀）和微粒体（150,000×g沉淀）组分中。暴露于低温后，由于CCT2水平增加，cct1植株的颗粒和微粒体组分具有更高的总CCT活性；相反，尽管总CCT活性显著增加，但cct2植株颗粒和微粒体组分中CCT1的水平保持不变。我们得出结论，拟南芥的CDP-胆碱途径在低温下通过同基因特异性模式上调：CCT2的表达增强以及膜中CCT1的翻译后激活/失活。在2℃下处理14天后，两个突变体和WS植株中的PC水平均得到类似维持，这表明任何一个CCT基因都足以在低温下进行PC生物合成。
