First published online October 3, 2002; 10.1104/pp.008110
Plant Physiol, October 2002, Vol. 130, pp. 740-756
Molecular Characterization of a Heteromeric ATP-Citrate Lyase
That Generates Cytosolic Acetyl-Coenzyme A in
Arabidopsis1,[w]
Beth L.
Fatland,
Jinshan
Ke,
Marc D.
Anderson,2
Wieslawa I.
Mentzen,
Li Wei
Cui,
C. Christy
Allred,
Jerry L.
Johnston,
Basil J.
Nikolau, and
Eve Syrkin
Wurtele*
Departments of Botany (B.L.F., J.K., M.D.A., W.I.M., E.S.W.) and
Biochemistry, Biophysics and Molecular Biology (L.W.C., C.C.A., J.L.J.,
B.J.N.) Iowa State University, Ames, Iowa 50011
Acetyl-coenzyme A (CoA) is used in the cytosol of
plant cells for the synthesis of a diverse set of phytochemicals
including waxes, isoprenoids, stilbenes, and flavonoids. The
source of cytosolic acetyl-CoA is unclear. We identified two
Arabidopsis cDNAs that encode proteins similar to the amino and carboxy
portions of human ATP-citrate lyase (ACL). Coexpression of these
cDNAs in yeast (Saccharomyces cerevisiae) confers ACL
activity, indicating that both the Arabidopsis genes are required for
ACL activity. Arabidopsis ACL is a heteromeric enzyme composed of two
distinct subunits, ACLA (45 kD) and ACLB (65 kD). The holoprotein has a
molecular mass of 500 kD, which corresponds to a heterooctomer with an
A4B4 configuration. ACL activity and the ACLA
and ACLB polypeptides are located in the cytosol, consistent with the
lack of targeting peptides in the ACLA and ACLB sequences. In the
Arabidopsis genome, three genes encode for the ACLA subunit
(ACLA-1, At1g10670; ACLA-2, At1g60810;
and ACLA-3, At1g09430), and two genes encode the ACLB subunit (ACLB-1, At3g06650 and ACLB-2,
At5g49460). The ACLA and ACLB mRNAs
accumulate in coordinated spatial and temporal patterns during plant
development. This complex accumulation pattern is consistent with the
predicted physiological needs for cytosolic acetyl-CoA, and is closely
coordinated with the accumulation pattern of cytosolic acetyl-CoA
carboxylase, an enzyme using cytosolic acetyl-CoA as a substrate. Taken
together, these results indicate that ACL, encoded by the
ACLA and ACLB genes of Arabidopsis,
generates cytosolic acetyl-CoA. The heteromeric organization of this
enzyme is common to green plants (including Chlorophyceae,
Marchantimorpha, Bryopsida, Pinaceae, monocotyledons, and eudicots),
species of fungi, Glaucophytes, Chlamydomonas, and
prokaryotes. In contrast, all known animal ACL enzymes have a homomeric
structure, indicating that a evolutionary fusion of the
ACLA and ACLB genes probably occurred
early in the evolutionary history of this kingdom.
1
This work was supported in part by grants from
the U.S. Department of Agriculture-National Research Initiative
Competitive Grants Program (grant nos. 2000-03447 and 2000-01436), by
the Department of Energy, Energy Biosciences Program (grant no.
DE-FG02-01ER15170), by Renessen, by the Iowa Soybean Promotion Board,
and by a Hermann Frasch Foundation Award (to E.S.W.).
2
Present address: Department of Botany/Biology,
323 Stevens Hall, North Dakota State University, Fargo, ND 58105.
[w]
The online version of this article contains Web-only
data. The supplemental material is available at www.plantphysiol.org.
*
Corresponding author; e-mail mash{at}iastate.edu; fax
515-294-1337.
© 2002 American Society of Plant Physiologists
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