Dennis L. Barton

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.

Cloning and characterization of an acyl‐CoA‐dependent diacylglycerol acyltransferase 1 (DGAT1) gene from Tropaeolum majus, and a study of the functional motifs of the DGAT protein using site‐directed mutagenesis to modify enzyme activity and oil content

SUMMARY A full-length cDNA encoding a putative diacylglycerol acyltransferase 1 (DGAT1, EC 2.3.1.20) was obtained from Tropaeolum majus (garden nasturtium). The 1557-bp open reading frame of this cDNA, designated TmDGAT1, encodes a protein of 518 amino acids showing high homology to other plant DGAT1s. The TmDGAT1 gene was expressed exclusively in developing seeds. Expression of recombinant TmDGAT1 in the yeast H1246MATalpha quadruple mutant (DGA1, LRO1, ARE1, ARE2) restored the capability of the mutant host to produce triacylglycerols (TAGs). The recombinant TmDGAT1 protein was capable of utilizing a range of (14)C-labelled fatty acyl-CoA donors and diacylglycerol acceptors, and could synthesize (14)C-trierucin. Collectively, these findings confirm that the TmDGAT1 gene encodes an acyl-CoA-dependent DGAT1. In plant transformation studies, seed-specific expression of TmDGAT1 was able to complement the low TAG/unusual fatty acid phenotype of the Arabidopsis AS11 (DGAT1) mutant. Over-expression of TmDGAT1 in wild-type Arabidopsis and high-erucic-acid rapeseed (HEAR) and canola Brassica napus resulted in an increase in oil content (3.5%-10% on a dry weight basis, or a net increase of 11%-30%). Site-directed mutagenesis was conducted on six putative functional regions/motifs of the TmDGAT1 enzyme. Mutagenesis of a serine residue in a putative SnRK1 target site resulted in a 38%-80% increase in DGAT1 activity, and over-expression of the mutated TmDGAT1 in Arabidopsis resulted in a 20%-50% increase in oil content on a per seed basis. Thus, alteration of this putative serine/threonine protein kinase site can be exploited to enhance DGAT1 activity, and expression of mutated DGAT1 can be used to enhance oil content.

Seed-Specific Heterologous Expression of a Nasturtium FAE Gene in Arabidopsis Results in a Dramatic Increase in the Proportion of Erucic Acid

The fatty acid elongase [often designated FAE or β-(or 3-) ketoacyl-CoA synthase] is a condensing enzyme and is the first component of the elongation complex involved in synthesis of erucic acid (22:1) in seeds of garden nasturtium (Tropaeolum majus). Using a degenerate primers approach, a cDNA of a putative embryo FAE was obtained showing high homology to known plant elongases. This cDNA contains a 1,512-bp open reading frame that encodes a protein of 504 amino acids. A genomic clone of the nasturtium FAE was isolated and sequence analyses indicated the absence of introns. Northern hybridization showed the expression of this nasturtium FAE gene to be restricted to the embryo. Southern hybridization revealed the nasturtium β-ketoacyl-CoA synthase to be encoded by a small multigene family. To establish the function of the elongase homolog, the cDNA was introduced into two different heterologous chromosomal backgrounds (Arabidopsis and tobacco [Nicotiana tabacum]) under the control of a seed-specific (napin) promoter and the tandem 35S promoter, respectively. Seed-specific expression resulted in up to an 8-fold increase in erucic acid proportions in Arabidopsis seed oil, while constitutive expression in transgenic tobacco tissue resulted in increased proportions of very long chain saturated fatty acids. These results indicate that the nasturtium FAE gene encodes a condensing enzyme involved in the biosynthesis of very long chain fatty acids, utilizing monounsaturated and saturated acyl substrates. Given its strong and unique preference for elongating 20:1-CoA, the utility of the FAE gene product for directing or engineering increased synthesis of erucic acid is discussed.

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.

Synthesis and field testing of enantiomers of 6Z,9Z-cis-3,4-epoxydienes as sex attractants for geometrid moths : Interactions of enantiomers and regioisomers.

Stereoselective syntheses of chiral C17 to C21 6Z,9Z-cis-3,4-epoxydienes were developed. Field tests of the enantiomerically enriched epoxides as components of synthetic sex attractant lures were carried out, and those with C17 and C19 chain lengths, particularly, were attractive to male moths of several species. Moths were usually specifically attracted by one of a pair of enantiomers, and the opposite enantiomer could actually be a behavioral antagonist. Males belonging to nine species of Geometridae were captured.Probole amicaria (Herrich-Schäffer) males were taken in traps baited with the mixture (6Z,9Z,3S,4R)-epoxy-nonadecadiene (6Z,9Z,3S,4R-epoxy-19∶H) + 3Z,9Z,6R,7S-epoxy-19∶H + 3Z,6Z,9Z-19∶H(9∶1∶8). Other species responding to the C19 compounds included (attractant components follow in parentheses);Sicya macularia (Harris) (6Z,9Z,3S,4R-epoxy-19∶H + 3Z,6Z,9Z-19∶H),Anavitrinella pampinaria (Guenée) (6Z,9Z-cis-3,4-epoxy-19∶H + 3Z,9Z,6S,7R-epoxy-19∶H), andLycia ursaria (Walker) (6Z,9Z-3S, 4R-epoxy-19∶H + 3Z,6Z,9Z-19∶H). Males of the following species were captured byC17 epoxides:Itame occiduaria (Packard) (6Z,9Z,3R,4S-epoxy-17∶H + 3Z,6Z,9Z-17∶H),Itame brunneata (Thunberg) (6Z,9Z,3S,4R-epoxy-17∶H),Epelis truncataria (Walker) (both enantiomers of 6Z,9Z-cis-3,4-epoxy-17∶H),Semiothisa ulsterata (Pearsall) (3Z,9Z-6S,7R-epoxy-17∶H), andS. signaria dispuncta (Walker) (3Z,9Z-cis-6,7-epoxy-17∶H + 3Z,6Z,9Z-17∶H). The interactions among enantiomers and regioisomers are discussed as a mechanism by which cross attraction between sympatric species is limited.

Sex pheromone components of three species ofSemiothisa (Geometridae), (Z,Z,Z)-3,6,9-heptadecatriene and two monoepoxydiene analogs

Adult males ofSemiothisa signaria dispuncta (Walker) were attracted to field traps baited with (Z,Z,Z)-3,6,9-octadecatriene and (Z,Z)-6,9-cis-3,4-epoxy-octadecadiene. However, analyses of sex pheromone gland extracts of females of this species by GC-MS and by GC in combination with an electroantennograph detector (GC-EAD) showed the pheromone to be comprised of a mixture of the next lower homologs: (Z,Z,Z)-3,6,9-heptadecatriene and (Z,Z)-6,9-cis-3,4-epoxy-heptadecadiene. Blends of these two C17 compounds were subsequently found to be more attractive to males in the field than the corresponding C18 mixtures. Sex pheromones of two otherSemiothisa species were also found to contain C17 components. (Z,Z,Z)-3,6,9-Heptadecatriene, detected by GC-EAD analysis of a female abdominal tip extract ofS. bicolorata (Fabricius), attracted conspecific males, and this attraction was significantly reduced by additions of (Z,Z)-6,9-cis-3,4-epoxyheptadecadiene, the major pheromone component ofS. signaria dispuncta, to the lure. (Z,Z)-3,9-cis-6,7-Epoxy-heptadecadiene was detected by GC-EAD analysis as the primary male antennal stimulatory component present in abdominal tip extracts ofS. ulsterata (Pearsall), and males of this species were attracted to traps baited with this epoxide. Each of these three C17 compounds constitute previously unknown lepidopteran sex pheromone components. Blends of (Z,Z, Z)-3,6,9-heptadecatriene and (Z,Z)-3,9-cis-6,7-epoxyheptadecadiene attracted males of a fourth species,S. delectata Hulst, but no females of this species were obtained to permit analysis of its sex pheromone. The occurrence of (Z,Z,Z)-3,6,9-heptadecatriene inS. neptaria (Guenee) females was indicated by GC-MS analysis of an abdominal tip extract; however, no males were attracted to any of the fielded mixtures containing this hydrocarbon.

Hairpin-RNA mediated silencing of endogenous FAD2 gene combined with heterologous expression of Crambe abyssinica FAE gene causes an increase in the level of erucic acid in transgenic Brassica carinata seeds

The 3′-UTR of the FAD2 gene from Brassica carinata was cloned by PCR and used to prepare an intron-spliced hairpin RNA (ihpRNA) construct. Compared to that of the wild type (WT) background, this construct, when expressed in B. carinata, resulted in a high degree of FAD2 gene silencing accompanied by strong increases of up to 16 and 10% in oleic acid and erucic acid proportions, respectively. The increase in 18:1 was accompanied by a concomitant proportional reduction in 18:2. A second construct containing ihpRNA targeted to the endogenous FAD2 gene in addition to the heterologous Crambe abyssinica FAE gene under the control of seed specific napin promoter, was used to transform B. carinata. This approach resulted in an even greater increase in erucic acid proportions, by up to 16% in T1 segregating seeds as compared to that of the WT control. To our knowledge, this is currently the highest accumulation of erucic acid achieved in B. carinata seeds using transgenic approaches, making it an increasingly-attractive alternative to high erucic B. napus cultivars as an industrial oil crop.

(3Z,6Z,9Z)-Nonadecatriene and enantiomers of (3Z,9Z)-cis-6,7-Epoxy-nonadecadiene as sex attractants for two geometrid and one noctuid moth species

Sex attractants for the geometrid mothsEufidonia convergaria andCaripeta angustiorata, and the noctuid mothRivula propinqualis have been elucidated during field screening of a series of (3Z,6Z,9Z)-triene hydrocarbons (C17–22), and the racemic and enantiomerically enriched monoepoxydienes derived from those hydrocarbons. Biologically active compounds were identified by a combination of field testing of synthetic standards, electroantennography, and coupled gas chromatography-electroantennogram detection.E. convergaria males were optimally attracted by a 1∶1 blend of (3Z,9Z)-(6S,7R)-epoxy-nonadecadiene (3Z,9Z-6S,7R-epoxy-19∶H); other abbreviations follow the same system) with (3Z,6Z,9Z)-nonadecatriene (3Z,6Z,9Z-19∶H). The 6R,7S enantiomer of the epoxide had no apparent biological activity, either as an attractant or as a behavioral antagonist. Male moths also were attracted to blends of the C18 and C20 homologs of the triene and the epoxide. 3Z,6Z,9Z-19∶H and 3Z,6Z-cis-6,7-epoxy-19∶H were identified inE. convergaria female pheromone gland extracts. Males of the geometrid moth speciesC. angustiorata were attracted by a 1∶1 blend of 3Z,6Z,9Z-19∶H and enantiomerically enriched 3Z,9Z-6R,7S-epoxy-19∶H. Males of the noctuid mothR. propinqualis were attracted by an approximately 10∶1 blend of 3Z,6Z,9Z-19∶H and enantiomerically enriched 3Z,9Z-6S, 7R-epoxy-19∶H. The components were synergistic, with neither being attractive alone. The blend ratio was quite specific, as the attractiveness of blends decreased sharply on either side of the optimum ratio.

3Z,6Z,9Z-trienes and unsaturated epoxides as sex attractants for geometrid moths.

Sex attractants for three species of geometrid moths were discovered during field screening of 3Z,6Z,9Z-trienes, and the racemic monoepoxydienes derived therefrom. MaleProbole amicaria moths were attracted to lure blends containing 6Z,9Z-cis-3,4-epoxy-nonadecadiene (6Z,9Z-cis-3,4-epoxy-19∶H) with 3Z,9Z-cis-6,7-epoxy-19∶H. 3Z,6Z,9Z-19∶H was positively identified and 6Z,9Z-cis-3,4-epoxy-19∶H was tentatively identified in extracts of female pheromone glands by coupled gas chromatography-electroantennogram detection (GC-EAD) and gas chromatography-mass spectrometry (GC-MS).Sicya macularia male moths were attracted by blends of 3Z,6Z,9Z-19∶H and 6Z,9Z-cis-3,4-epoxy-19∶H. The attractive response was strongly antagonized by small amounts of 3Z,9Z-cis-6,7-epoxy-19∶H, or by larger amounts of 3Z,6Z-cis-9,10-epoxy-19∶H.Lomographa semiclarata male moths were attracted by a variety of lures containing 3Z,6Z,9Z-17∶H as a major component. 3Z,6Z,9Z-17∶H was tentatively identified in a female pheromone gland extract by GC-EAD.