Samuel L. MacKenzie

Modification of seed oil content and acyl composition in the brassicaceae by expression of a yeast sn-2 acyltransferase gene.

A putative yeast sn-2 acyltransferase gene (SLC1-1), reportedly a variant acyltransferase that suppresses a genetic defect in sphingolipid long-chain base biosynthesis, has been expressed in a yeast SLC deletion strain. The SLC1-1 gene product was shown in vitro to encode an sn-2 acyltransferase capable of acylating sn-1 oleoyl-lysophosphatidic acid, using a range of acyl-CoA thioesters, including 18:1-, 22:1-, and 24:0-CoAs. The SLC1-1 gene was introduced into Arabidopsis and a high erucic acid-containing Brassica napus cv Hero under the control of a constitutive (tandem cauliflower mosaic virus 35S) promoter. The resulting transgenic plants showed substantial increases of 8 to 48% in seed oil content (expressed on the basis of seed dry weight) and increases in both overall proportions and amounts of very-long-chain fatty acids in seed triacylglycerols (TAGs). Furthermore, the proportion of very-long-chain fatty acids found at the sn-2 position of TAGs was increased, and homogenates prepared from developing seeds of transformed plants exhibited elevated lysophosphatidic acid acyltransferase (EC 2.3.1.51) activity. Thus, the yeast sn-2 acyltransferase has been shown to encode a protein that can exhibit lysophosphatidic acid acyltransferase activity and that can be used to change total fatty acid content and composition as well as to alter the stereospecific acyl distribution of fatty acids in seed TAGs.

Alteration of Seed Fatty Acid Composition by an Ethyl Methanesulfonate-Induced Mutation in Arabidopsis thaliana Affecting Diacylglycerol Acyltransferase Activity

In characterizing the enzymes involved in the formation of very long-chain fatty acids (VLCFAs) in the Brassicaceae, we have generated a series of mutants of Arabidopsis thaliana that have reduced VLCFA content. Here we report the characterization of a seed lipid mutant, AS11, which, in comparison to wild type (WT), has reduced levels of 20:1 and 18:1 and accumulates 18:3 as the major fatty acid in triacylglycerols. Proportions of 18:2 remain similar to WT. Genetic analyses indicate that the fatty acid phenotype is caused by a semidominant mutation in a single nuclear gene, designated TAG1, located on chromosome 2. Biochemical analyses have shown that the AS11 phenotype is not due to a deficiency in the capacity to elongate 18:1 or to an increase in the relative [delta]15 or [delta]12 desaturase activities. Indeed, the ratio of desaturase/elongase activities measured in vitro is virtually identical in developing WT and AS11 seed homogenates. Rather, the fatty acid phenotype of AS11 is the result of reduced diacylglycerol acyltransferase activity throughout development, such that triacylglycerol biosynthesis is reduced. This leads to a reduction in 20:1 biosynthesis during seed development, leaving more 18:1 available for desaturation. Thus, we have demonstrated that changes to triacylglycerol biosynthesis can result in dramatic changes in fatty acid composition and, in particular, in the accumulation of VLCFAs in seed storage lipids.

High-Level Production of γ-Linolenic Acid in Brassica juncea Using a Δ6 Desaturase from Pythium irregulare

γ-Linolenic acid (GLA), a nutritionally important fatty acid in mammals, is synthesized by a Δ6 desaturase. Here, we report identification of PiD6, a new cDNA from the oleaginous fungus, Pythium irregulare, encoding a 459-amino acid protein that shares sequence similarity to carboxyl-directed desaturases from various species. Expression ofPiD6 in yeast (Saccharomyces cerevisiae) revealed that it converts exogenously supplied linoleic acid into GLA, indicating that it encodes a Δ6 fatty acid desaturase. Expression of the desaturase in Brassica juncea under the control of the Brassica napus napin promoter resulted in production of three Δ6 unsaturated fatty acids (18:2–6, 9; 18:3–6, 9, 12; and 18:4–6, 9, 12, 15) in seeds. Among them, GLA (18:3–6, 9, 12) is the most abundant and accounts for up to 40% of the total seed fatty acids. Lipid class and positional analysis indicated that GLA is almost exclusively incorporated into triacylglycerol (98.5%) with only trace amounts found in the other lipids. Within triacylglycerols, GLA is more abundant at the sn-2 position.

Gas-liquid chromatography of N-heptafluorobutyryl isobutyl esters of amino acids☆

Abstract The N-heptafluorobutyryl isobutyl esters of the protein amino acids have been separated by gas-liquid chromatography using a single column of 3% SE-30 on Gas-Chrom Q. The separation is superior to that of previous single-column methods and is particularly suitable for the analysis of plant seed proteins. The method is also applicable to glycoproteins.

Enhancement of seed oil content by expression of glycerol-3-phosphate acyltransferase genes

Arabidopsis thaliana was transformed with a plastidial safflower glycerol-3-phosphate acyltransferase (GPAT) and an Escherichia coli GPAT. The genes were used directly and in modified forms with, as applicable, the plastidial targeting sequence removed, and with an endoplasmic reticulum targeting sequence added. Seeds of plants transformed using only the vector were indistinguishable in oil content from wild-type control plants. All other gene constructs increased seed oil content. The unmodified safflower gene (spgpat) produced oil increases ranging from 10 to 21%. On average, the greatest increase (+22%) was observed in seeds of transformants carrying the spgpat with the targeting peptide removed. The E. coli plsB gene increased seed oil content by an average of 15%.

Analysis of amino acids by gas—liquid chromatography as tert.-butyldimethylsilyl derivatives : Preparation of derivatives in a single reaction

The effect of temperature, solvent and reagents on the formation of the N(O)-dimethyl-tert.-butylsilyl derivatives of proteic amino acids has been studied. Quantitative silylation is achieved using dimethyl-tert.-butylsilyltrifluoroacetamide with 1% tert.-butyldimethylchlorosilane in dimethylformamide by heating at 75 degrees C for 30 min. Two peaks were obtained for arginine under these conditions. However, most of the standard proteic amino acids can be assayed. The N(O)-dimethyl-tert.-butylsilyl derivatives of the proteic amino acids have been analysed by gas chromatography-mass spectrometry using the methane chemical ionization mode. The spectral data are presented and have been used to confirm the structures of the amino acid derivatives.

Utility of the Arabidopsis FAE1 and yeast SLC1-1 genes for improvements in erucic acid and oil content in rapeseed.

High-erucic acid (HEA) Brassica napus cultivars are regaining interest in industrial contexts. Erucic acid and its derivatives are important renewable raw materials utilized in the manufacture of plastic films, in the synthesis of Nylon 13,13, and in the lubricant and emollient industries. Theoretically, the highest level of erucic acid that can be achieved by means of classical breeding is 66 mol%; however, using new approaches on the basis of genetic engineering, it might be possible to develop a B. napus cultivar containing levels of erucic acid significantly above 66 mol% (>80 mol%). In an attempt to increase the amounts of very-long-chain fatty acids (VLCFAs), and erucic acid in particular, in Canadian HEA B. napus cultivars, we have focused on two targets using a transgenic approach. We examined both the role/function of the Arabidopsis thaliana FAE1 (fatty acid elongase) gene by expressing it under the control of the seed-specific napin promoter in B. napus germplasm with analysis of the changes in VLCFA content in the seed oil of transgenic lines, and the performance of the yeast SLC1-1 (sphingolipid compensation mutant) in B. napus cv. Hero transgenic progeny in the field. Here, we report analyses of the contents of 22:1, total VLCFAand oil in the seed oil, as well as seed yield of the field-grown FAE1 and SLC1-1 B. napus cv. Hero progeny.

Isolation and characterization of a Δ5 FA desaturase from Pythium irregulare by heterologous expression in Saccharomyces cerevisiae and oilseed crops

By using the polymerase chain reaction approach with two degenerate primers targeting the heme-binding and the third histidine-rich motifs in microsomal carboxyl-directed desaturases, we identified a cDNA PiD5 from Pythium irregulare encoding a Δ5 desaturase. The substrate specificity of the enzyme was studied in detail by expressing PiD5 in a yeast (Saccharomyces cerevisiae) mutant strain, AMY-2α, where ole1, a Δ9 desaturase gene, is disrupted. The result revealed that the encoded enzyme could desaturate unsaturated FA from 16 to 20 carbons beginning with Δ9 and Δ11 as well as Δ8 ethylenic double bonds. Introduction of PiD5 into Brassica juncea under the control of a CaMV 35S constitutive promoter resulted in accumulation of several Δ5-unsaturated polymethylene-interrupted FA (Δ5-UPIFA) including 18∶2−5,9, 18∶2−5,11, 18∶3−5,9,12, and 18∶4−5,9,12,15 in vegetative tissues. The transgenic enzyme could also desaturate the exogenously supplied homo-γ-linolenic acid (20∶3−8,11,14) to arachidonic acid (20∶4−5,8,11,14). Introduction of PiD5 into B. juncea and flax under the control of seed-specific promoters resulted in production of Δ5-UPIFA, representing more than 10% of the total FA in the seeds.

Gas chromatography—mass spectrometry of the N(O)-heptafluorobutyryl isobutyl esters of the protein amino acids using electron impact ionisation☆

The N(O)-heptafluorobutyryl isobutyl esters of the protein amino acids have been analysed by combined gas chromatography-mass spectrometry using electron impact ionisation. The spectral data have been used to confirm the structures of the amino acid derivatives.

Stereospecific analyses of seed triacylglycerols from high-erucic acid brassicaceae: Detection of erucic acid at thesn-2 position inBrassica oleracea L. Genotypes

Stereospecific analyses of triacylglycerols from selected high-erucic acid breeding lines or cultivars ofBrassica napus L. andB. oleracea L. have been performed. Initial lipase screening revealed that while allB. napus lines contained little or no erucic acid at thesn-2 position, several of theB. oleracea lines had significant proportions of erucic acid at this position. Detailed stereospecific analyses were performed on the triacylglycerols from these lines by using a Grignard-based deacylation, conversion of thesn-1,sn-2 andsn-3 monoacylglycerols to their di-dinitrophenyl urethane (DNPU) derivatives, resolution of the di-DNPU-monoacylglycerols (MAGs) by high-performance liquid chromatography on a chiral column, transmethylation of eachsn-di-DNPU MAG fraction and analysis of the resulting fatty acid methyl esters by gas chromatography. The findings unequivocally demonstrate for the first time that, within the Brassicaceae, there existsB. oleracea germplasm containing seed oils with substantial erucic acid (30–35 mol%) at thesn-2 position. This has important implications for biotechnology and breeding efforts designed to increase the levels of erucic acid in rapeseed beyond 66 mol% to supply strategic industrial feedstocks. In the first instance, the germplasm will be of direct use in retrieving a gene encoding aBrassica lyso-phosphatidic acid acyltransferase with an affinity for erucoyl-CoA. In a breeding program, the germplasm offers promise for the introduction of this trait intoB. napus by interspecific hybridization and embryo rescue.