Formation of conjugated delta8,delta10-double bonds by delta12-oleic-acid desaturase-related enzymes: biosynthetic origin of calendic acid.
Divergent forms of the plant Delta(12)-oleic-acid desaturase (FAD2) have previously been shown to catalyze the formation of acetylenic bonds, epoxy groups, and conjugated Delta(11),Delta(13)-double bonds by modification of an existing Delta(12)-double bond in C(18) fatty acids. Here, we report a class of FAD2-related enzymes that modifies a Delta(9)-double bond to produce the conjugated trans-Delta(8),trans-Delta(10)-double bonds found in calendic acid (18:3Delta(8trans,10trans,12cis)), the major component of the seed oil of Calendula officinalis. Using an expressed sequence tag approach, cDNAs for two closely related FAD2-like enzymes, designated CoFADX-1 and CoFADX-2, were identified from a C. officinalis developing seed cDNA library. The deduced amino acid sequences of these polypeptides share 40-50% identity with those of other FAD2 and FAD2-related enzymes. Expression of either CoFADX-1 or CoFADX-2 in somatic soybean embryos resulted in the production of calendic acid. In embryos expressing CoFADX-2, calendic acid accumulated to as high as 22% (w/w) of the total fatty acids. In addition, expression of CoFADX-1 and CoFADX-2 in Saccharomyces cerevisiae was accompanied by calendic acid accumulation when induced cells were supplied exogenous linoleic acid (18:2Delta(9cis,12cis)). These results are thus consistent with a route of calendic acid synthesis involving modification of the Delta(9)-double bond of linoleic acid. Regiospecificity for Delta(9)-double bonds is unprecedented among FAD2-related enzymes and further expands the functional diversity found in this family of enzymes.
Cahoon
E B
EB
DuPont Nutrition and Health, Experimental Station, Wilmington, Delaware 19880-0402, USA. Edgar.B.Cahoon@usa.dupont.com
Ripp
K G
KG
Hall
S E
SE
Kinney
A J
AJ
D000595:Amino Acid Sequence; D020838:Calendula / Q000201:enzymology* / Q000235:genetics; D003001:Cloning, Molecular; D044943:Fatty Acid Desaturases / Q000235:genetics / Q000378:metabolism*; D005231:Fatty Acids, Unsaturated / Q000096:biosynthesis*; D015723:Gene Library; D019787:Linoleic Acid / Q000378:metabolism; D008969:Molecular Sequence Data; D019301:Oleic Acid / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics / Q000378:metabolism; D030821:Plants, Genetically Modified; D010946:Plants, Medicinal; D012639:Seeds / Q000201:enzymology / Q000235:genetics; D017386:Sequence Homology, Amino Acid; D013025:Glycine max / Q000235:genetics
D005231:Fatty Acids, Unsaturated; D010940:Plant Proteins; D019301:Oleic Acid; C428441:calendic acid; D019787:Linoleic Acid; D044943:Fatty Acid Desaturases; C428442:FADX-1 protein, Calendula officinalis; C428443:FADX-2 protein, Calendula officinalis; C040448:delta-12 fatty acid desaturase