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Plant and Cell Physiology Advance Access originally published online on August 10, 2009
Plant and Cell Physiology 2009 50(10):1727-1735; doi:10.1093/pcp/pcp115
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© The Author 2009. Published by Oxford University Press on behalf of Japanese Society of Plant Physiologists. All rights reserved. For permissions, please email: journals.permissions@oxfordjournals.org

Isozyme-Specific Modes of Activation of CTP:Phosphorylcholine Cytidylyltransferase in Arabidopsis thaliana at Low Temperature

Rie Inatsugi1, Hiromitsu Kawai2, Yasuyo Yamaoka2, Yanbo Yu2, Akira Sekiguchi2, Masanobu Nakamura1 and Ikuo Nishida2,*

1Department of Biological Sciences, Graduate School of Science, The University of Tokyo, Hongo 7-3-1, Bunkyo-ku, Tokyo, 113-0033 Japan
2Area of Biochemistry and Molecular Biology, Division of Life Science, Graduate School of Science and Engineering, Saitama University, Saitama, Japan

*Corresponding author: E-mail, nishida{at}molbiol.saitama-u.ac.jp; Fax, +81-48-858-3384.


  Abstract

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 [EC] ), 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°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°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°C, suggesting that either of the CCT genes is sufficient for PC biosynthesis at low temperature.

Keywords: Arabidopsis thaliana - CDP–choline pathway - Cold acclimation - Membrane expansion - Phosphati-dylcholine - Post-translational regulation

Abbreviations: CCT, CTP:phosphorylcholine cytidylyl-transferase; Col, Columbia; PC, phosphatidylcholine; PFD, photon flux density; WS, Wassilevskaja

(Received March 7, 2009; Accepted April 4, 2009)
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