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Published online on March 5, 2007, 10.1073/pnas.0611141104
PNAS | March 13, 2007 | vol. 104 | no. 11 | 4742-4747


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BIOLOGICAL SCIENCES / PLANT BIOLOGY
Modulating seed beta-ketoacyl-acyl carrier protein synthase II level converts the composition of a temperate seed oil to that of a palm-like tropical oil

Mark S. Pidkowich, Huu Tam Nguyen, Ingo Heilmann*, Till Ischebeck*, and John Shanklin{dagger}

Department of Biology, Brookhaven National Laboratory, Upton, NY 11973

Edited by George H. Lorimer, University of Maryland, College Park, MD, and approved January 22, 2007 (received for review December 14, 2006)

beta-Ketoacyl-acyl carrier protein (ACP) synthase II (KASII) elongates 16:0-ACP to 18:0-ACP in the plastid, where it competes with three other enzymes at the first major branch point in fatty acid biosynthesis. Despite its key metabolic location, the influence of KASII in determining seed oil composition remains unclear, in part because the biochemical consequences of the fab1-1 mutation were unresolved. Thus, fab1-1, and a newly identified knockout allele, fab1-2, were analyzed in the context of the hypothesis that modulating KASII activity is sufficient to convert the composition of a temperate seed oil into that of a palm-like tropical oil. No homozygous fab1-2 individuals were identified in progeny of self-fertilized heterozygous fab1-2 plants, {approx}1/4 of which aborted before the torpedo stage, suggesting that fab1-2 represents a complete loss of function and results in lethality when homozygous. Consistent with this hypothesis, homozygous fab1-2 plants were identified when a fab1-1 transgene was introduced, demonstrating that fab1-1 encodes an active KASII. Strong seed-specific hairpin-RNAi reductions in FAB1 expression resulted in abortion of {approx}1/4 of the embryos in an apparent phenocopy of fab1-2 homozygosity. In less severe FAB1 hairpin-RNAi individuals, embryos developed normally and exhibited a 1:2:1 segregation ratio for palmitate accumulation. Thus, early embryo development appears sensitive to elevated 16:0, whereas at later stages, up to 53% of 16:0, i.e., a 7-fold increase over wild-type levels, is tolerated. These results resolve the role of KASII in seed metabolism and demonstrate that modulation of Arabidopsis KASII levels is sufficient to convert its temperate oilseed composition to that of a palm-like tropical oil.

condensing enzyme | fatty acid biosynthesis | metabolic engineering | plant oil

Author contributions: M.S.P. and H.T.N. contributed equally to this work; M.S.P., H.T.N., and J.S. designed research; M.S.P., H.T.N., I.H., and T.I. performed research; M.S.P., H.T.N., I.H., and J.S. analyzed data; and M.S.P., H.T.N., and J.S. wrote the paper.

*Present address: Department of Plant Biochemistry, Albrecht-von-Haller-Institute for Plant Sciences, Georg-August-Universität Göttingen, 37077 Göttingen, Germany.

The authors declare no conflict of interest.

This article is a PNAS direct submission.

{dagger}To whom correspondence should be addressed. E-mail: shanklin{at}bnl.gov

© 2007 by The National Academy of Sciences of the USA


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