Cloning of a higher-plant plastid omega-6 fatty acid desaturase cDNA and its expression in a cyanobacterium.
Oligomers based on amino acids conserved between known plant omega-3 and cyanobacterium omega-6 fatty acid desaturases were used to screen an Arabidopsis cDNA library for related sequences. An identified clone encoding a novel desaturase-like polypeptide was used to isolate its homologs from Glycine max and Brassica napus. The plant deduced amino acid sequences showed less than 27% similarity to known plant omega-6 and omega-3 desaturases but more than 48% similarity to cyanobacterial omega-6 desaturase, and they contained putative plastid transit sequences. Thus, we deduce that the plant cDNAs encode the plastid omega-6 desaturase. The identity was supported by expression of the B. napus cDNA in cyanobacterium. Synechococcus transformed with a chimeric gene that contains a prokaryotic promoter fused to the rapeseed cDNA encoding all but the first 73 amino acids partially converted its oleic acid fatty acid to linoleic acid, and the 16:1(9c) fatty acid was converted primarily to 16:2(9c, 12) in vivo. Thus, the plant omega-6 desaturase, which utilizes 16:1(7c) in plants, can utilize 16:1(9c) in the cyanobacterium. The plastid and cytosolic homologs of plant omega-6 desaturases are much more distantly related than those of omega-3 desaturases.
Hitz
W D
WD
E.I. duPont de Nemours & Co., Experimental Station, Wilmington, Delaware 19880-0402.
Carlson
T J
TJ
Booth
J R
JR
Kinney
A J
AJ
Stecca
K L
KL
Yadav
N S
NS
D000595:Amino Acid Sequence; D017360:Arabidopsis / Q000201:enzymology / Q000235:genetics; D001483:Base Sequence; D003001:Cloning, Molecular; D017124:Conserved Sequence; D000458:Cyanobacteria / Q000235:genetics; D018076:DNA, Complementary / Q000235:genetics*; D044943:Fatty Acid Desaturases / Q000235:genetics*; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated; D015870:Gene Expression; D017343:Genes, Plant; D008969:Molecular Sequence Data; D010944:Plants / Q000201:enzymology / Q000235:genetics; D018087:Plastids / Q000201:enzymology; D017386:Sequence Homology, Amino Acid
D018076:DNA, Complementary; D043371:Fatty Acids, Omega-6; D005231:Fatty Acids, Unsaturated; D044943:Fatty Acid Desaturases