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Published on July 11, 2008; 10.1104/pp.108.123331

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Received May 21, 2008
Accepted July 6, 2008

Overexpression of the Arabidopsis 10-kD Acyl-CoA-Binding Protein, ACBP6, Enhances Freezing Tolerance

Qin-Fang Chen , Shi Xiao , and Mee-Len Chye *

School of Biological Sciences, The University of Hong Kong, Pokfulam Road, Hong Kong, China

* Corresponding author; email: mlchye{at}hkucc.hku.hk.

Small 10-kD acyl-CoA-binding proteins (ACBPs) are highly-conserved proteins that are prevalent in eukaryotes. In Arabidopsis thaliana, other than the 10-kD ACBP homologue (designated as Arabidopsis ACBP6), there are 5 larger forms of ACBPs ranging from 37.5 to 73.1 kD. In this study, the cytosolic subcellular localization of Arabidopsis ACBP6 was confirmed by analyses on transgenic Arabidopsis expressing autofluorescence-tagged ACBP6 and western blot analysis of subcellular fractions using ACBP6-specific antibodies. The expression of Arabidopsis ACBP6 was noticeably induced at 48 h after 4 oC treatment in northern blot analysis and western blot analysis. Further, an acbp6 T-DNA insertional mutant that lacked ACBP6 mRNA and protein, displayed increased sensitivity to freezing temperature (-8 oC), while ACBP6-overexpressing transgenic Arabidopsis were conferred enhanced freezing tolerance. Northern blot analyses indicated that ACBP6-associated freezing tolerance was not dependent on induction of cold-regulated COR gene expression. Instead, ACBP6-overexpressors showed increased expression of mRNA encoding phospholipase D{delta} (PLD{delta}). Lipid profiling analyses on cold-acclimated freezing-treated (-8 oC) transgenic Arabidopsis plants overexpressing ACBP6 showed a decline in phosphatidylcholine (-36% and -46%) and elevation of phosphatidic acid (73% and 67%) in comparison to wild type. From our comparison, the gain in freezing tolerance in ACBP6-overexpressors that were accompanied by decreases in phosphatidylcholine and accumulation in phosphatidic acid is consistent with previous findings on PLD{delta}-overexpressing transgenic Arabidopsis. In vitro filter-binding assays indicating His-tagged ACBP6 binds phosphatidylcholine, but not phosphatidic acid or lysophosphatidylcholine, further implicates a role for ACBP6 in phospholipid metabolism in Arabidopsis.






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