GENETIC ENHANCEMENT OF SOYBEAN SEED VALUE BY BIOTECHNOLOGY
Location: Plant Genetics Research
Title: IDENTIFICATION AND FUNCTIONAL CHARACTERIZATION OF THE MOSS PHYSCOMITRELLA PATENS DELTA5-DESATURASE GENE INVOLVED IN ARACHIDONIC AND EICOSAPENTAENOIC ACID BIOSYNTHESIS
| Kaewsuwan, Songsri - MAHIDOL UNIVERSITY |
| Cahoon, Edgar |
| Perroud, Pierre-Francois - WASHINGTON UNIVERSITY |
| Bunyapraphatsara, Nuntavan - MAHIDOL UNIVERSITY |
| Wiwat, Chanpen - MAHIDOL UNIVERSITY |
| Panvisavas, Nathinee - MAHIDOL UNIVERSITY |
| Quantrano, Ralph - WASHINGTON UNIVERSITY |
| Cove, David - WASHINGTON UNIVERSITY |
Submitted to: Journal of Biological Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: May 12, 2006
Publication Date: August 4, 2006
Citation: Kaewsuwan, S., Cahoon, E.B., Perroud, P., Bunyapraphatsara, N., Wiwat, C., Panvisavas, N., Quantrano, R.S., Cove, D.J. 2006. Identification and functional characterization of the moss physcomitrella patens delta5-desaturase gene involved in arachidonic and eicosapentaenoic acid biosynthesis. Journal of Biological Chemistry. 281:21988-21997.
Interpretive Summary: Omega-3 polyunsaturated fatty acids (or PUFAs), such as those found in fish oils, are important components of a heart healthy diet and are also desired components of feed for the aquaculture industry. These fatty acids, however, are absent from the vegetable oils of the major oilseed crops, including soybean. Considerable attention has been directed at producing omega-3 PUFAs in crop plants in order to increase their nutritive and economic value. As a step towards achieving this goal, we report in this manuscript the identification and characterization of a gene for a fatty acid desaturase from a moss species. We show that this enzyme catalyzes a key step in the biosynthesis of the omega-3 PUFA eicosapentaenoic acid, which is a major component of fish oils. The availability of this gene will facilitate efforts by plant molecular biologists and geneticists to develop genetically enhanced crops that produce healthier and higher value vegetable oils. This research will ultimately expand the uses of crops produced by US farmers and will result in more nutritious foods for consumers and improved feed for the aquaculture industry.
The moss Physcomitrella patens contains high levels of arachidonic acid and lesser amounts of eicosapentaenoic acid. In general, these C20 polyunsaturated fatty acids are synthesized from linoleic and alpha-linolenic acids, respectively, by a series of reactions catalyzed by a delta6-desaturase, an ELO-like enzyme involved in delta6-elongation and a delta5-desaturase. Here we report the identification and characterization of a delta5-desaturase from P. patens. A full-length cDNA for this desaturase was identified by database searches based on homology to sequences of known delta5-desaturase cDNAs from fungal and algal species. The P. patens cDNA that was isolated based on these searches encodes a 480 amino acids polypeptide that contains a predicted N-terminal cytochrome b5-like domain, as well as three histidine-rich domains. Expression of the enzyme in Saccharomyces cerevisiae resulted in the production of the delta5-containing fatty acid arachidonic acid in cells that were provided di-homo-gamma-linolenic acid. In addition, the expressed enzyme generated delta5-desaturation products with the C20 substrates omega-6 eicosadienoic and omega-3 eicosatrienoic acids, but no products were detected with the C18 fatty acids linoleic and alpha-linolenic acids nor with the C22 fatty acids adrenic and docosapentaenoic acids. As an alternative proof of this protein’s function, the corresponding P. patens was disrupted by replacement with a positive selection marker through homologous recombination. Gene disruption resulted in a dramatic alteration in the fatty acid composition of P. patens, with an increase in di-homo-gamma-linolenic and eicosatetraenoic acids and a concomitant disappearance of the delta5-fatty acids arachidonic and eicosapentaenoic acids. In addition, over-expression of this gene in protoplasts isolated from a disrupted line, resulted in the restoration of arachidonic acid synthesis.