TY - JOUR
T1 - An unusual seed-specific 3-ketoacyl-ACP synthase associated with the biosynthesis of petroselinic acid in coriander
AU - Mekhedov, Sergei
AU - Cahoon, Edgar B.
AU - Ohlrogge, John
N1 - Funding Information:
We thank Dr Anthony Kinney (DuPont Crop Genetics) for providing a KAS IIx tobacco cDNA clone and valuable advice. This work was supported by a grant from the Michigan Soybean Promotion Board. Acknowledgment is also extended to the Michigan Agricultural Experiment Station for its support of this research.
PY - 2001
Y1 - 2001
N2 - Petroselinic acid (18:1 Δ6) is the major component of the seed oil of Umbelliferae species such as coriander (Coriandrum sativum) as well as Araliaceae and Garryaceae species. This unusual fatty acid is synthesized in plastids by the Δ4 desaturation of palmitoyl-acyl carrier protein (16:0-ACP) and subsequent elongation of Δ4-hexadecenoyl (16:1 Δ4)-ACP. To characterize the enzymatic nature of the elongation reaction, an in vitro assay was developed with 16:1 Δ4-ACP and 16:0-ACP as substrates. Extracts from developing coriander seeds elongated 16:1 Δ4-ACP in a competitive assay at rates ten-fold greater than that with 16:0-ACP. In contrast, extracts from castor seeds, which do not synthesize petroselinic acid, displayed a strong preference for the elongation of 16:0-ACP rather than 16:1 Δ4-ACP. In addition, the elongation of 16:1 Δ4-ACP and 16:0-ACP by coriander seed extracts was strongly inhibited by cerulenin at concentrations as low as 10 μM. This finding suggested that the elongation of 16:1 Δ4-ACP and 16:0-ACP in coriander seed is catalyzed by a 3-ketoacyl-ACP synthase (KAS) I-type enzyme(s), rather than a KAS II-type activity that is typically associated with 16:0-ACP elongation. Consistent with this, a cDNA for a diverged form of KAS I was isolated from a cDNA library prepared from developing coriander seed. Using a variety of heterologous probing techniques, no KAS II-type cDNAs could be identified in this library. Multiple alignment of KAS amino acid sequences indicated that, although the polypeptide corresponding to the coriander cDNA is more closely related to KAS I, its active site motif deviates from those found in both KAS I and KAS II enzymes. Also suggestive of a possible role in petroselinic acid synthesis, antibodies raised to the recombinant protein recognize an abundant 45 kDa polypeptide in coriander endosperm that is not detected in coriander leaves. These antibodies also recognize a major band of similar size in developing seeds of English ivy (Hedera helix), an Araliaceae species that also accumulates petroselinic acid in a seed-specific manner.
AB - Petroselinic acid (18:1 Δ6) is the major component of the seed oil of Umbelliferae species such as coriander (Coriandrum sativum) as well as Araliaceae and Garryaceae species. This unusual fatty acid is synthesized in plastids by the Δ4 desaturation of palmitoyl-acyl carrier protein (16:0-ACP) and subsequent elongation of Δ4-hexadecenoyl (16:1 Δ4)-ACP. To characterize the enzymatic nature of the elongation reaction, an in vitro assay was developed with 16:1 Δ4-ACP and 16:0-ACP as substrates. Extracts from developing coriander seeds elongated 16:1 Δ4-ACP in a competitive assay at rates ten-fold greater than that with 16:0-ACP. In contrast, extracts from castor seeds, which do not synthesize petroselinic acid, displayed a strong preference for the elongation of 16:0-ACP rather than 16:1 Δ4-ACP. In addition, the elongation of 16:1 Δ4-ACP and 16:0-ACP by coriander seed extracts was strongly inhibited by cerulenin at concentrations as low as 10 μM. This finding suggested that the elongation of 16:1 Δ4-ACP and 16:0-ACP in coriander seed is catalyzed by a 3-ketoacyl-ACP synthase (KAS) I-type enzyme(s), rather than a KAS II-type activity that is typically associated with 16:0-ACP elongation. Consistent with this, a cDNA for a diverged form of KAS I was isolated from a cDNA library prepared from developing coriander seed. Using a variety of heterologous probing techniques, no KAS II-type cDNAs could be identified in this library. Multiple alignment of KAS amino acid sequences indicated that, although the polypeptide corresponding to the coriander cDNA is more closely related to KAS I, its active site motif deviates from those found in both KAS I and KAS II enzymes. Also suggestive of a possible role in petroselinic acid synthesis, antibodies raised to the recombinant protein recognize an abundant 45 kDa polypeptide in coriander endosperm that is not detected in coriander leaves. These antibodies also recognize a major band of similar size in developing seeds of English ivy (Hedera helix), an Araliaceae species that also accumulates petroselinic acid in a seed-specific manner.
KW - 3-ketoacyl-ACP synthase
KW - Coriandrum sativum
KW - Petroselinic acid
KW - Seed-specific expression
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U2 - 10.1023/A:1011832611885
DO - 10.1023/A:1011832611885
M3 - Article
C2 - 11669576
AN - SCOPUS:0034792407
SN - 0167-4412
VL - 47
SP - 507
EP - 518
JO - Plant Molecular Biology
JF - Plant Molecular Biology
IS - 4
ER -