Koo, AJKAJKKooFulda, MartinMartinFuldaBrowse, J.J.BrowseOhlrogge, J. B.J. B.Ohlrogge2018-11-072018-11-072005https://resolver.sub.uni-goettingen.de/purl?gro-2/49653Plant cells are known to elongate exogenously provided fatty acid (FA), but the subcellular sites and mechanisms for this process are not currently understood. When Arabidopsis leaves were incubated with C-14-FAs with <= 16 carbons, the label appeared in elongated and desaturated products. Laurate elongation was 85% inhibited by 50 mu m cerulenin, an inhibitor of ketoacyl-acyl carrier protein (ACP) synthetase I/II. In contrast, haloxyfop, an inhibitor of cytosolic acetyl-coenzyme A (CoA) carboxylase, inhibited only elongation into very long chain FAs (>= 20 carbons) but not synthesis of C-14-unsaturated 18-carbon or 16-carbon FAs. Isolated pea chloroplasts were also able to elongate C-14-FAs (<= 16 carbons) in the light. No detectable C-14-acyl-CoA intermediates were formed during C-14-laurate elongation, whereas C-14-acyl-ACP accumulated to 2.3 mu m. These data indicate that the elongation of exogenous medium-chain FAs to 16- and 18-carbon FAs occurs primarily in the chloroplasts, most likely via the enzymes of de novo FA synthesis. An Arabidopsis mutant with a T-DNA insertion in At4g14070 (AAE15) was reduced 80% in C-14-laurate elongation into 16- and 18-carbon FAs. AAE15 has sequence similarity to long-chain acyl-CoA synthetases and a predicted N-terminal plastidial targeting sequence. Direct acyl-ACP-forming activity from FA and ACP was observed in extracts of Arabidopsis leaves and isolated chloroplasts but aae15 plants had markedly reduced in vitro acyl-ACP synthesis activity. Together these results demonstrate that plants possess a mechanism for direct activation of FA to ACP in the plastid via an acyl-ACP synthetase encoded by At4g14070.journal_article10.1111/j.1365-313X.2005.02553.x16262711000232868400008