Increase in lysophosphatidate acyltransferase activity in oilseed rape (Brassica napus) increases seed triacylglycerol content despite its low intrinsic flux control coefficient

BnLPAT2 gene regulates oil accumulation in Brassica napus by modulating linoleic and linolenic acid levels in seeds

Lysophosphatidate acyltransferase (LPAT) catalyzes the conversion of lysophosphatidic acid to phosphatidic acid, a key step in lipid biosynthesis. This study cloned four LPAT2 genes from Brassica napus: BnLPAT2-A04, A07, A09, and C08. Functional analysis using bioinformatics, qRT-PCR (Quantitative Reverse Transcription Polymerase Chain Reaction), CRISPR/Cas9 (Clustered Regularly Interspaced Short Palindromic Repeats/CRISPR-associated protein 9), overexpression, and transcriptome sequencing revealed that these genes encode proteins containing the conserved PLN02380 domain. BnLPAT2-A07/A09/C08 showed strong conservation with Arabidopsis AtLPAT2. Promoter analysis revealed multiple cis-elements related to stress, light, and phytohormone responses, with the BnLPAT2-A09/C08 promoters containing the most diverse cis-elements. Expression analysis showed that BnLPAT2-A07/C08 was highly expressed in various tissues, with BnLPAT2-A07 peaking during seed development. Overexpression of these genes increased seed oil content and the proportion of C18:2/C18:3 fatty acids, with BnLPAT2-A07 achieving an increase in oil content ranging from 4.46% to 6.44%. Gene knockout reduced oil content by 7.5% and affected fatty acid accumulation. Transcriptome sequencing analysis suggested that the BnLPAT2 genes promote the production of long-chain fatty acids, such as Linoleic acid (C18:2) and Linolenic acid (C18:3), through biological processes, including fatty acid biosynthesis, very long-chain fatty acid biosynthesis, and very long-chain fatty acid metabolism, thereby improving seed oil content. This study provides valuable insights into lipid metabolism and offers a theoretical foundation for improving oil content and fatty acid composition in B. napus.

Effect of Heterologous Expression of Key Enzymes Involved in Astaxanthin and Lipid Synthesis on Lipid and Carotenoid Production in Aurantiochytrium sp

Aurantiochytrium sp., a heterotrophic microorganism, has received increasing attention for its high production of polyunsaturated fatty acids and has been widely applied in various industries. This study intended to optimize the carotenoid synthesis pathway in Aurantiochytrium sp. by metabolic engineering to increase the carotenoid content. Multi-sourced key enzyme genes involved in lipid synthesis (LPAAT and DGAT) and astaxanthin synthesis (crtZ and crtW) were selected to construct single-gene expression vectors and transformed into Aurantiochytrium sp. The results showed that the overexpression of LPAAT of Phaeodactylum tricornutum in Aurantiochytrium sp. caused an increase of 39.3% in astaxanthin, 424.7% in β-carotene, 901.8% in canthaxanthin, and 575.9% in lutein, as well as a down-regulation of 15.3% in the fatty acid content. Transcriptomics analysis revealed enhanced expression of genes involved in purine and amino acid metabolism in the transformed strains, and the down-regulation of the citric acid cycle led to an increase in the source of acetyl coenzyme A for the production of fatty acids. This study provides strong experimental evidence to support the application of increasing carotenoid levels in Aurantiochytrium sp.

Understanding the triacylglycerol-based carbon anabolic differentiation in Cyperus esculentus and Cyperus rotundus developing tubers via transcriptomic and metabolomic approaches

BACKGROUND

Yellow nutsedge (Cyperus esculentus, known as 'YouShaDou' in China, YSD) and purple nutsedge (Cyperus rotundus, known as 'XiangFuZi' in China, XFZ), closely related Cyperaceae species, exhibit significant differences in triacylglycerol (TAG) accumulation within their tubers, a key factor in carbon flux repartitioning that highly impact the total lipid, carbohydrate and protein metabolisms. Previous studies have attempted to elucidate the carbon anabolic discrepancies between these two species, however, a lack of comprehensive genome-wide annotation has hindered a detailed understanding of the underlying molecular mechanisms.

RESULTS

This study utilizes transcriptomic analyses, supported by a comprehensive YSD reference genome, and metabolomic profiling to uncover the mechanisms underlying the major carbon perturbations between the developing tubers of YSD and XFZ germplasms harvested in Yunnan province, China, where the plant biodiveristy is renowned worldwide and may contain more genetic variations relative to their counterparts in other places. Our findings indicate distinct expression patterns of key regulatory genes involved in TAG biosynthesis and lipid droplet formation, including transcriptional factors and structural genes such as ABI3 transcriptional factor, rate-limiting enzymes GPAT3/6/9 and DGAT2/3, and oleosin and caleosin homologs. Furthermore, our omics data suggest that these differences in gene expression are not the sole contributors to the diverse tuber compositions. Instead, complex interactions among highly regulated catalytic reactions, governing carbohydrate, protein, and species-specific metabolite metabolisms, such as starch and sucrose metabolic pathways, flavonoid and amino acids biosynthetic pathways, collectively contribute to the pronounced carbon anabolic differentiation primarily evident in TAG accumulation, as well as the starch properties in mature tubers.

CONCLUSION

This study offers new metabolic insights into the high-value underground non-photosynthetic tissues of Cyperaceae species, which harbors not only high biomass productivity but also abundant nutrients as favorable food or industrial sources in the modern agriculture. The detailed omics analyses aim to deepen our understanding of the Cyperaceae species, which may potentially broaden their application values and facilitate the molecular breeding of better varieties to ameliorate the food safety problem.

Increasing oil content in Brassica oilseed species

Brassica oilseed species are the third most important in the world, providing approximately 15 % of the total vegetable oils. Three species (Brassica rapa, B. juncea, B. napus) dominate with B. napus being the most common in Canada, China and Europe. Originally, B. napus was a crop producing seed with high erucic acid content, which still persists today, to some extent, and is used for industrial purposes. In contrast, cultivars which produce seed used for food and feed are low erucic acid cultivars which also have reduced glucosinolate content. Because of the limit to agricultural land, recent efforts have been made to increase productivity of oil crops, including Brassica oilseed species. In this article, we have detailed research in this regard. We have covered modern genetic, genomic and metabolic control analysis approaches to identifying potential targets for the manipulation of seed oil content. Details of work on the use of quantitative trait loci, genome-wide association and comparative functional genomics to highlight factors influencing seed oil accumulation are given and functional proteins which can affect this process are discussed. In summary, a wide variety of inputs are proving useful for the improvement of Brassica oilseed species, as major sources of global vegetable oil.

Trehalose-6-phosphate synthase 8 increases photosynthesis and seed yield in Brassica napus

Trehalose-6-phosphate (T6P) functions as a vital proxy for assessing carbohydrate status in plants. While class II T6P synthases (TPS) do not exhibit TPS activity, they are believed to play pivotal regulatory roles in trehalose metabolism. However, their precise functions in carbon metabolism and crop yield have remained largely unknown. Here, BnaC02.TPS8, a class II TPS gene, is shown to be specifically expressed in mature leaves and the developing pod walls of Brassica napus. Overexpression of BnaC02.TPS8 increased photosynthesis and the accumulation of sugars, starch, and biomass compared to wild type. Metabolomic analysis of BnaC02.TPS8 overexpressing lines and CRISPR/Cas9 mutants indicated that BnaC02.TPS8 enhanced the partitioning of photoassimilate into starch and sucrose, as opposed to glycolytic intermediates and organic acids, which might be associated with TPS activity. Furthermore, the overexpression of BnaC02.TPS8 not only increased seed yield but also enhanced seed oil accumulation and improved the oil fatty acid composition in B. napus under both high nitrogen (N) and low N conditions in the field. These results highlight the role of class II TPS in impacting photosynthesis and seed yield of B. napus, and BnaC02.TPS8 emerges as a promising target for improving B. napus seed yield.

Polyunsaturated Fatty Acids: Conversion to Lipid Mediators, Roles in Inflammatory Diseases and Dietary Sources

Polyunsaturated fatty acids (PUFAs) are important components of the diet of mammals. Their role was first established when the essential fatty acids (EFAs) linoleic acid and α-linolenic acid were discovered nearly a century ago. However, most of the biochemical and physiological actions of PUFAs rely on their conversion to 20C or 22C acids and subsequent metabolism to lipid mediators. As a generalisation, lipid mediators formed from n-6 PUFAs are pro-inflammatory while those from n-3 PUFAs are anti-inflammatory or neutral. Apart from the actions of the classic eicosanoids or docosanoids, many newly discovered compounds are described as Specialised Pro-resolving Mediators (SPMs) which have been proposed to have a role in resolving inflammatory conditions such as infections and preventing them from becoming chronic. In addition, a large group of molecules, termed isoprostanes, can be generated by free radical reactions and these too have powerful properties towards inflammation. The ultimate source of n-3 and n-6 PUFAs are photosynthetic organisms which contain Δ-12 and Δ-15 desaturases, which are almost exclusively absent from animals. Moreover, the EFAs consumed from plant food are in competition with each other for conversion to lipid mediators. Thus, the relative amounts of n-3 and n-6 PUFAs in the diet are important. Furthermore, the conversion of the EFAs to 20C and 22C PUFAs in mammals is rather poor. Thus, there has been much interest recently in the use of algae, many of which make substantial quantities of long-chain PUFAs or in manipulating oil crops to make such acids. This is especially important because fish oils, which are their main source in human diets, are becoming limited. In this review, the metabolic conversion of PUFAs into different lipid mediators is described. Then, the biological roles and molecular mechanisms of such mediators in inflammatory diseases are outlined. Finally, natural sources of PUFAs (including 20 or 22 carbon compounds) are detailed, as well as recent efforts to increase their production.

Metabolic Control Analysis of triacylglycerol accumulation in oilseed rape

The increasing global demand for vegetable oils will only be met if there are significant improvements in the productivity of the major oil crops, such as oilseed rape. Metabolic engineering offers the prospect of further gains in yield beyond that already achieved by breeding and selection but requires guidance as to the changes that need to be made. Metabolic Control Analysis, through measurement and estimation of flux control coefficients, can indicate which enzymes have the most influence on a desired flux. Some experiments have previously reported flux control coefficients for oil accumulation in the seeds of oilseed rape, and others have measured control coefficient distributions for multi-enzyme segments of oil synthesis in seed embryo metabolism measured in vitro. In addition, other reported manipulations of oil accumulation contain results that are exploited further here to calculate previously unknown flux control coefficients. These results are then assembled within a framework that allows an integrated interpretation of the controls on oil accumulation from the assimilation of CO₂ to deposition of oil in the seed. The analysis shows that the control is distributed to an extent that the gains from amplifying any single target are necessarily limited, but there are candidates for joint amplification that are likely to act synergistically to produce much more significant gains.

Class A lysophosphatidic acid acyltransferase 2 from Camelina sativa promotes very long-chain fatty acids accumulation in phospholipid and triacylglycerol

Very long-chain fatty acids (VLCFAs) are important industrial raw materials and can be produced by genetically modified oil plants. For a long time, class A lysophosphatidic acid acyltransferase (LPAT) was considered unable to promote the accumulation of VLCFA in oil crops. The bottlenecks that the transgenic high VLCFA lines have an oil content penalty and the low amount of VLCFA in phosphatidylcholine remains intractable. In the present study, a class A LPAT2 from Camelina sativa (CsaLPAT2) promoting VLCFAs accumulation in phospholipid was found. Overexpression of CsaLPAT2 alone in Arabidopsis seeds significantly increased the VLCFA content in triacylglycerol, including C20:0, C20:2, C20:3, C22:0, and C22:1. The proportion of phosphatidic acid molecules containing VLCFAs in transgenic seeds reached up to 45%, which was 2.8-fold greater than that in wild type. The proportion of phosphatidylcholine and diacylglycerol molecules containing VLCFAs also increased significantly. Seed size in CsaLPAT2 transgenic lines showed a slight increase without an oil content penalty. The total phospholipid content in the seed of the CsaLPAT2 transgenic line was significantly increased. Furthermore, the function of class A LPAT in promoting the accumulation of VLCFAs is conserved in the representative oil crops of Brassicaceae, such as C. sativa, Arabidopsis thaliana, Brassica napus, Brassica rapa, and Brassica oleracea. The findings of this study provide a promising gene resource for the production of VLCFAs.

LYSOPHOSPHATIDIC ACID ACYLTRANSFERASE 2 (LPAT2) is required for de novo glycerolipid biosynthesis, growth, and development in vegetative and reproductive tissues of Arabidopsis

The Kennedy pathway is a highly conserved de novo glycerolipid biosynthesis pathway in prokaryotes and eukaryotes. In Arabidopsis, LYSOPHOSPHATIDIC ACID ACYLTRANSFERASE 2 (LPAT2) was assumed to catalyze a crucial reaction step of the endoplasmic reticulum (ER)-localized Kennedy pathway because of lethality in the lpat2-1 knockout mutant. However, whether this lethal phenotype was due to the essential role of the Kennedy pathway or LPAT2 as the key enzyme of the Kennedy pathway was unclear. By creating non-lethal LPAT2-knockdown mutants in Arabidopsis, we found that LPAT2 is required for phospholipid content and plant development in vegetative and reproductive growth. Functional in vivo reporter assays revealed that LPAT2 was ubiquitously expressed and localized to the ER, where de novo phospholipid biosynthesis takes place. Intriguingly, our lipid analysis revealed that LPAT2 suppression had different effects among the organs examined: phospholipid levels were decreased both in leaves and flowers and the effect was more pronounced in flowers, a non-photosynthetic organ enriched with phospholipids. Although seed size was reduced in the LPAT2 suppression lines, no remarkable effect was observed in the lipid content of mature siliques. Our results show that LPAT2 is involved in the ER-localized Kennedy pathway, and suggest that its contribution to de novo phospholipid biosynthesis may have organ selectivity.

Lysophosphatidic acid acyltransferase 2 and 5 commonly, but differently, promote seed oil accumulation in Brassica napus

Background

Increasing seed oil content (SOC) of Brassica napus has become one of the main plant breeding goals over the past decades. Lysophosphatidic acid acyltransferase (LPAT) performs an important molecular function by regulating the production of phosphatidic acid (PA), a key intermediate in the synthesis of membrane and storage lipids. However, the mechanism underlying the effect of LPAT on the SOC of B. napus remains unclear.

Results

In the present study, significant elevation of SOC was achieved by overexpressing BnLPAT2 and BnLPAT5 in B. napus. RNAi and CRISPR–Cas9 were also successfully used to knock down and knock out these two genes in B. napus where SOC significantly decreased. Meanwhile, we found an accumulation of lipid droplets and oil bodies in seeds of BnLPAT2 and BnLPAT5 overexpression lines, whereas an increase of sugar and protein in Bnlpat2 and Bnlpat5 mutant seeds. Sequential transcriptome analysis was further performed on the developing seeds of the BnLPAT2 and BnLPAT5 overexpression, knockdown, and knockout rapeseed lines. Most differentially expressed genes (DEGs) that were expressed in the middle and late stages of seed development were enriched in photosynthesis and lipid metabolism, respectively. The DEGs involved in fatty acid and lipid biosynthesis were active in the overexpression lines but were relatively inactive in the knockdown and knockout lines. Further analysis revealed that the biological pathways related to fatty acid/lipid anabolism and carbohydrate metabolism were specifically enriched in the BnLPAT2 overexpression lines.

Conclusions

BnLPAT2 and BnLPAT5 are essential for seed oil accumulation. BnLPAT2 preferentially promoted diacylglycerol synthesis to increase SOC, whereas BnLPAT5 tended to boost PA synthesis for membrane lipid generation. Taken together, BnLPAT2 and BnLPAT5 can jointly but differently promote seed oil accumulation in B. napus. This study provides new insights into the potential mechanisms governing the promotion of SOC by BnLPAT2 and BnLPAT5 in the seeds of B. napus.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13068-022-02182-2.

BnaPPT1 is essential for chloroplast development and seed oil accumulation in Brassica napus

INTRODUCTION

Phosphoenolpyruvate/phosphate translocator (PPT) transports phosphoenolpyruvate from the cytosol into the plastid for fatty acid (FA) and other metabolites biosynthesis.

OBJECTIVES

This study investigated PPTs' functions in plant growth and seed oil biosynthesis in oilseed crop Brassica napus.

METHODS

We created over-expression and mutant material of BnaPPT1. The plant development, oil content, lipids, metabolites and ultrastructure of seeds were compared to evaluate the gene function.

RESULTS

The plastid membrane localized BnaPPT1 was found to be required for normal growth of B. napus. The plants grew slower with yellowish leaves in BnaA08.PPT1 and BnaC08.PPT1 double mutant plants. The results of chloroplast ultrastructural observation and lipid analysis show that BnaPPT1 plays an essential role in membrane lipid synthesis and chloroplast development in leaves, thereby affecting photosynthesis. Moreover, the analysis of primary metabolites and lipids in developing seeds showed that BnaPPT1 could impact seed glycolytic metabolism and lipid level. Knockout of BnaA08.PPT1 and BnaC08.PPT1 resulted in decreasing of the seed oil content by 2.2 to 9.1%, while overexpression of BnaC08.PPT1 significantly promoted the seed oil content by 2.1 to 3.3%.

CONCLUSION

Our results suggest that BnaPPT1 is necessary for plant chloroplast development, and it plays an important role in maintaining plant growth and promoting seed oil accumulation in B. napus.

Acyl-CoA:diacylglycerol acyltransferase: Properties, physiological roles, metabolic engineering and intentional control

Acyl-CoA:diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) catalyzes the last reaction in the acyl-CoA-dependent biosynthesis of triacylglycerol (TAG). DGAT activity resides mainly in membrane-bound DGAT1 and DGAT2 in eukaryotes and bifunctional wax ester synthase-diacylglycerol acyltransferase (WSD) in bacteria, which are all membrane-bound proteins but exhibit no sequence homology to each other. Recent studies also identified other DGAT enzymes such as the soluble DGAT3 and diacylglycerol acetyltransferase (EaDAcT), as well as enzymes with DGAT activities including defective in cuticular ridges (DCR) and steryl and phytyl ester synthases (PESs). This review comprehensively discusses research advances on DGATs in prokaryotes and eukaryotes with a focus on their biochemical properties, physiological roles, and biotechnological and therapeutic applications. The review begins with a discussion of DGAT assay methods, followed by a systematic discussion of TAG biosynthesis and the properties and physiological role of DGATs. Thereafter, the review discusses the three-dimensional structure and insights into mechanism of action of human DGAT1, and the modeled DGAT1 from Brassica napus. The review then examines metabolic engineering strategies involving manipulation of DGAT, followed by a discussion of its therapeutic applications. DGAT in relation to improvement of livestock traits is also discussed along with DGATs in various other eukaryotic organisms.

Tandem Mass Tag-Based Quantitative Proteomics Reveals Implication of a Late Embryogenesis Abundant Protein (BnLEA57) in Seed Oil Accumulation in Brassica napus L

Enhancing oil content is one of the major goals in Brassica napus breeding; however, genetic regulation of seed oil content in plants is complex and not fully elucidated. In this study, we report proteins that were differentially accumulated in immature seeds of 35 days after anthesis between two recombinant inbred lines with contrasting seed oil content, high oil content line (HOCL) and low oil content line (LOCL) using a multiplex isobaric tandem mass tags (TMT)-based quantitative proteomic approach. Over 4,600 proteins were quantified in seeds of the two lines, and 342 proteins showed differential accumulation between seeds of HOCL and LOCL. Gene Ontology enrichment analysis revealed that the differentially accumulated proteins were enriched in proteins involved in lipid biosynthesis and metabolism, photosynthesis, and nutrient reservoir activity. Western blot confirmed the increased abundance of a late embryogenesis abundant protein (BnLEA57) in HOCL seeds compared with LOCL seeds, and overexpression of either BnLEA57 gene or its homology BnLEA55 in transgenic Arabidopsis thaliana enhanced oil content in Arabidopsis seeds. Our work provides new insights into the molecular regulatory mechanism of seed oil content in B. napus.

Overexpression of phospholipid: diacylglycerol acyltransferase in Brassica napus results in changes in lipid metabolism and oil accumulation

The regulation of lipid metabolism in oil seeds is still not fully understood and increasing our knowledge in this regard is of great economic, as well as intellectual, importance. Oilseed rape (Brassica napus) is a major global oil crop where increases in triacylglycerol (TAG) accumulation have been achieved by overexpression of relevant biosynthetic enzymes. In this study, we expressed Arabidopsis phospholipid: diacylglycerol acyltransferase (PDAT1), one of the two major TAG-forming plant enzymes in B. napus DH12075 to evaluate its effect on lipid metabolism in developing seeds and to estimate its flux control coefficient. Despite several-fold increase in PDAT activity, seeds of three independently generated PDAT transgenic events showed a small but consistent decrease in seed oil content and had altered fatty acid composition of phosphoglycerides and TAG, towards less unsaturation. Mass spectrometry imaging of seed sections confirmed the shift in lipid compositions and indicated that PDAT overexpression altered the distinct heterogeneous distributions of phosphatidylcholine (PC) molecular species. Similar, but less pronounced, changes in TAG molecular species distributions were observed. Our data indicate that PDAT exerts a small, negative, flux control on TAG biosynthesis and could have under-appreciated effects in fine-tuning of B. napus seed lipid composition in a tissue-specific manner. This has important implications for efforts to increase oil accumulation in similar crops.

Transgenic manipulation of triacylglycerol biosynthetic enzymes in B. napus alters lipid-associated gene expression and lipid metabolism

Oilseed rape (Brassica napus) is an important crop that is cultivated for the oil (mainly triacylglycerol; TAG) it produces in its seeds. TAG synthesis is controlled mainly by key enzymes in the Kennedy pathway, such as glycerol 3-phosphate acyltransferase (GPAT), lysophosphatidate acyltransferase (LPAT) and diacylglycerol acyltransferase (DGAT) but can also be produced from phosphoglycerides such as phosphatidylcholine (PC) by the activity of the enzyme phospholipid: diacylglycerol acyltransferase (PDAT). To evaluate the potential for these enzymes to alter oil yields or composition, we analysed transgenic B. napus lines which overexpressed GPAT, LPAT or PDAT using heterologous transgenes from Arabidopsis and Nasturtium and examined lipid profiles and changes in gene expression in these lines compared to WT. Distinct changes in PC and TAG abundance and spatial distribution in embryonic tissues were observed in some of the transgenic lines, together with altered expression of genes involved generally in acyl-lipid metabolism. Overall our results show that up-regulation of these key enzymes differentially affects lipid composition and distribution as well as lipid-associated gene expression, providing important information which could be used to improve crop properties by metabolic engineering.

The effect of AINTEGUMENTA-LIKE 7 over-expression on seed fatty acid biosynthesis, storage oil accumulation and the transcriptome in Arabidopsis thaliana

AIL7 over-expression modulates fatty acid biosynthesis and triacylglycerol accumulation in Arabidopsis developing seeds through the transcriptional regulation of associated genes. Seed fatty acids (FAs) and triacylglycerol (TAG) contribute to many functions in plants, and seed lipids have broad food, feed and industrial applications. As a result, an enormous amount of attention has been dedicated towards uncovering the regulatory cascade responsible for the fine-tuning of the lipid biosynthetic pathway in seeds, which is regulated in part through the action of LEAFY COTYLEDON1, ABSCISSIC ACID INSENSITIVE 3, FUSCA3 and LEC2 (LAFL) transcription factors. Although AINTEGUMENTA-LIKE 7 (AIL7) is involved in meristematic function and shoot phyllotaxy, its effect in the context of lipid biosynthesis has yet to be assessed. Here, we generated AIL7 seed-specific over-expression lines and found that they exhibited significant alterations in FA composition and decreased total lipid accumulation in seeds. Seeds and seedlings from transgenic lines also exhibited morphological deviations compared to wild type. Correspondingly, RNA-Seq analysis demonstrated that the expression of many genes related to FA biosynthesis and TAG breakdown were significantly altered in developing siliques from transgenic lines compared to wild-type plants. The seed-specific over-expression of AIL7 also altered the expression profiles of many genes related to starch metabolism, photosynthesis and stress response, suggesting further roles for AIL7 in plants. These findings not only advance our understanding of the lipid biosynthetic pathway in seeds, but also provide evidence for additional functions of AIL7, which could prove valuable in downstream breeding and/or metabolic engineering endeavors.

Working with Randy: The Diacylglycerol Acyltransferase Story

Vegetable oils are one of the main agricultural commodities. Demand has been increasing steadily over the last five decades and, with finite land available, it is vital that we increase productivity. My laboratory has focused on the regulation of plant lipid metabolism and, as part of this work, we identified diacylglycerol acyltransferase (DGAT) as important at regulating carbon flux during oil accumulation. This led to collaborations with Randy Weselake's research group when we quantified the importance of DGAT in oilseed rape by using flux control analysis. Later, with David Taylor, we showed that over-expression of DGAT boosted oil accumulation in field-grown crops by around 8%. These studies led to a multitude of experiments with different oil crops, such as oil palm and soybean, as well as many rewarding collaborations with Randy.

Functional Characterization of Lysophosphatidylcholine: Acyl-CoA Acyltransferase Genes From Sunflower (Helianthus annuus L.)

Lysophosphatidylcholine acyltransferase (LPCAT, EC 2.3.1.23) is an evolutionarily conserved key enzyme in the Lands cycle that catalyzes acylation of lysophosphatidylcholine (LPC) to produce phosphatidylcholine (PC), the main phospholipid in cellular membranes. In this study, three LPCAT genes from sunflower were identified and the corresponding proteins characterized. These HaLPCAT genes encoded functionally active enzymes that were able to complement a deficient yeast mutant. Moreover, enzymatic assays were carried out using microsomal preparations of the yeast cells. When acyl specificities were measured in the forward reaction, these enzymes exhibited a substrate preference for unsaturated acyl-CoAs, especially for linolenoyl-CoA, while in the reverse reaction, linoleoyl or linolenoyl acyl groups were transferred from PC to acyl-CoA to a similar extent. Expression levels of LPCAT genes were studied revealing distinct tissue-specific expression patterns. In summary, this study suggests that the combined forward and reverse reactions catalyzed by sunflower LPCATs facilitate acyl-exchange between the sn-2 position of PC and the acyl-CoA pool. Sunflower LPCATs displayed different characteristics, which could point to different functionalities, favoring the enrichment of seed triacylglycerols (TAGs) with polyunsaturated fatty acid (PUFA).