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Involvement of Arabidopsis ACYL-COENZYME A DESATURASE-LIKE2 (At2g31360) in the Biosynthesis of the Very-Long-Chain Monounsaturated Fatty Acid Components of Membrane Lipids1[W]
The Arabidopsis ( Arabidopsis thaliana ) acyl-coenzyme A (CoA) desaturase-like (ADS) gene family contains nine genes encoding fatty acid desaturase-like proteins. The biological function of only one member of the family, fatty acid desaturase5 ( AtADS3 / FAD5 , At3g15850), is known, and this gene en...
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Published in: | Plant physiology (Bethesda) 2012-11, Vol.161 (1), p.81-96 |
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Main Authors: | , , , , , , , , |
Format: | Article |
Language: | English |
Subjects: | |
Online Access: | Get full text |
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Summary: | The Arabidopsis (
Arabidopsis thaliana
) acyl-coenzyme A (CoA) desaturase-like (ADS) gene family contains nine genes encoding fatty acid desaturase-like proteins. The biological function of only one member of the family, fatty acid desaturase5 (
AtADS3
/
FAD5
, At3g15850), is known, and this gene encodes the plastidic palmitoyl-monogalactosyldiacylglycerol Δ7 desaturase. We cloned seven members of the gene family that are predicted not to have a chloroplast transit peptide and expressed them in the yeast
Saccharomyces cerevisiae
. All seven have previously undescribed desaturase activity on very-long-chain fatty acid (
VLCFA
) substrates and exhibit diverse regiospecificity, catalyzing introduction of double bonds relative to the methyl end of the molecule (
n-x
) at
n
-6 (
AtADS4
, At1g06350),
n
-7 (
AtADS1.3
, At1g06100 and
AtADS4.2
, At1g06360),
n
-9 (
AtADS1
, At1g06080 and
AtADS2
, At2g31360) or Δ9 (relative to the carboxyl end of the molecule) positions (
AtADS1.2
, At1g06090 and
AtADS1.4
, At1g06120). Through forward and reverse genetics it was shown that
AtADS2
is involved in the synthesis of the 24:1(
n
-9) and 26:1(
n
-9) components (X:Y, where X is chain length and Y is number of double bonds) of seed lipids, sphingolipids, and the membrane phospholipids phosphatidylserine, and phosphatidylethanolamine. Plants deficient in
AtADS2
expression showed no obvious phenotype when grown under normal growing conditions, but showed an almost complete loss of phosphatidylethanolamine(42:4), phosphatidylserine(42:4), dihydroxy-monohexosylceramide(42:2)-2, trihydroxy-monohexosylceramide(42:2)-3, and trihydroxy-glycosylinositolphosphoceramide(42:2)-3, lipid species that contain the
VLCFA
24:1(
n
-9), and trihydroxy-glycosylinositolphosphoceramide(44:2)-3, a lipid containing 26:1(
n
-9). Acyl-CoA profiling of these plants revealed a major reduction in 24:1-CoA and a small reduction in 26:1-CoA. Overexpression of
AtADS2
resulted in a substantial increase in the percentage of glycerolipid and sphingolipids species containing 24:1 and a dramatic increase in the percentage of very-long-chain monounsaturated fatty acids in the acyl-CoA pool. Plants deficient in
AtADS1
expression had reduced levels of 26:1(
n
-9) in seed lipids, but no significant changes in leaf phospholipids or sphingolipids were observed. These findings indicate that the 24-carbon and 26-carbon monounsaturated
VLCFAs
of Arabidopsis result primarily from
VLCFA
desaturation, rather than by elongati |
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ISSN: | 0032-0889 1532-2548 |
DOI: | 10.1104/pp.112.202325 |