Seed-specific over-expression of an Arabidopsis cDNA encoding a diacylglycerol acyltransferase enhances seed oil content and seed weight

A Novel Soybean Diacylglycerol Acyltransferase 1b Variant with Three Amino Acid Substitutions Increases Seed Oil Content

Improving soybean (Glycine max) seed composition by increasing the protein and oil components will add significant value to the crop and enhance environmental sustainability. Diacylglycerol acyltransferase (DGAT) catalyzes the final rate-limiting step in triacylglycerol biosynthesis and has a major impact on seed oil accumulation. We previously identified a soybean DGAT1b variant modified with 14 amino acid substitutions (GmDGAT1b-MOD) that increases total oil content by 3 percentage points when overexpressed in soybean seeds. In the present study, additional GmDGAT1b variants were generated to further increase oil with a reduced number of substitutions. Variants with one to four amino acid substitutions were screened in the model systems Saccharomyces cerevisiae and transient Nicotiana benthamiana leaf. Promising GmDGAT1b variants resulting in high oil accumulation in the model systems were selected for overexpression in soybeans. One GmDGAT1b variant with three novel amino acid substitutions (GmDGAT1b-3aa) increased total soybean oil to levels near the previously discovered GmDGAT1b-MOD variant. In a multiple location field trial, GmDGAT1b-3aa transgenic events had significantly increased oil and protein by up to 2.3 and 0.6 percentage points, respectively. The modeling of the GmDGAT1b-3aa protein structure provided insights into the potential function of the three substitutions. These findings will guide efforts to improve soybean oil content and overall seed composition by CRISPR editing.

Variety of Plant Oils: Species-Specific Lipid Biosynthesis

Plant oils represent a large group of neutral lipids with important applications in food, feed and oleochemical industries. Most plants accumulate oils in the form of triacylglycerol within seeds and their surrounding tissues, which comprises three fatty acids attached to a glycerol backbone. Different plant species accumulate unique fatty acids in their oils, serving a range of applications in pharmaceuticals and oleochemicals. To enable the production of these distinctive oils, select plant species have adapted specialized oil metabolism pathways, involving differential gene co-expression networks and structurally divergent enzymes/proteins. Here, we summarize some of the recent advances in our understanding of oil biosynthesis in plants. We compare expression patterns of oil metabolism genes from representative species, including Arabidopsis thaliana, Ricinus communis (castor bean), Linum usitatissimum L. (flax) and Elaeis guineensis (oil palm) to showcase the co-expression networks of relevant genes for acyl metabolism. We also review several divergent enzymes/proteins associated with key catalytic steps of unique oil accumulation, including fatty acid desaturases, diacylglycerol acyltransferases and oleosins, highlighting their structural features and preference toward unique lipid substrates. Lastly, we briefly discuss protein interactomes and substrate channeling for oil biosynthesis and the complex regulation of these processes.

Integrated Transcriptomic and Metabolomic Analysis Reveal the Dynamic Process of Bama Hemp Seed Development and the Accumulation Mechanism of α-Linolenic Acid and Linoleic Acid

Bama County is a world-famous longevity county in the Guangxi Province, China. Bama hemp is a traditional seed used in hemp cultivation in the Bama County. The seeds contain abundant unsaturated fatty acids, particularly linoleic acid (LA) and linolenic acid in the golden ratio. These two substances have been proven to be related to human health and the prevention of various diseases. However, the seed development and seed oil accumulation mechanisms remain unclear. This study employed a combined analysis of physiological, transcriptomic, and metabolomic parameters to elucidate the fatty acid formation patterns in Bama hemp seeds throughout development. We found that seed oil accumulated at a late stage in embryo development, with seed oil accumulation following an "S″-shaped growth curve, and positively correlated with seed size, sugar content, protein content, and starch content. Transcriptome analysis identified genes related to the metabolism of LA, α-linolenic acid (ALA), and jasmonic acid (JA). We found that the FAD2 gene was upregulated 165.26 folds and the FAD3 gene was downregulated 6.15 folds at day 21. Metabolomic changes in LA, ALA, and JA compounds suggested a competitive relationship among these substances. Our findings indicate that the peak period of substance accumulation and nutrient accumulation in Bama hemp seeds occurs during the midstage of seed development (day 21) rather than in the late stage (day 40). The results of this research will provide a theoretical basis for local cultivation and deep processing of Bama hemp.

Comparative transcriptomic analysis provides insights into the genetic networks regulating oil differential production in oil crops

BACKGROUND

Plants differ more than threefold in seed oil contents (SOCs). Soybean (Glycine max), cotton (Gossypium hirsutum), rapeseed (Brassica napus), and sesame (Sesamum indicum) are four important oil crops with markedly different SOCs and fatty acid compositions.

RESULTS

Compared to grain crops like maize and rice, expanded acyl-lipid metabolism genes and relatively higher expression levels of genes involved in seed oil synthesis (SOS) in the oil crops contributed to the oil accumulation in seeds. Here, we conducted comparative transcriptomics on oil crops with two different SOC materials. In common, DIHYDROLIPOAMIDE DEHYDROGENASE, STEAROYL-ACYL CARRIER PROTEIN DESATURASE, PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE, and oil-body protein genes were both differentially expressed between the high- and low-oil materials of each crop. By comparing functional components of SOS networks, we found that the strong correlations between genes in "glycolysis/gluconeogenesis" and "fatty acid synthesis" were conserved in both grain and oil crops, with PYRUVATE KINASE being the common factor affecting starch and lipid accumulation. Network alignment also found a conserved clique among oil crops affecting seed oil accumulation, which has been validated in Arabidopsis. Differently, secondary and protein metabolism affected oil synthesis to different degrees in different crops, and high SOC was due to less competition of the same precursors. The comparison of Arabidopsis mutants and wild type showed that CINNAMYL ALCOHOL DEHYDROGENASE 9, the conserved regulator we identified, was a factor resulting in different relative contents of lignins to oil in seeds. The interconnection of lipids and proteins was common but in different ways among crops, which partly led to differential oil production.

CONCLUSIONS

This study goes beyond the observations made in studies of individual species to provide new insights into which genes and networks may be fundamental to seed oil accumulation from a multispecies perspective.

Overexpression of the Phosphatidylcholine:DiacylglycerolCholinephosphotransferase (PDCT) gene increases carbon flux toward triacylglycerol (TAG) synthesis in Camelinasativa seeds

Camelinasativa has considerable promise as a dedicated industrial oilseed crop. Its oil-based blends have been tested and approved as liquid transportation fuels. Previously, we utilized metabolomic and transcriptomic profiling approaches and identified metabolic bottlenecks that control oil production and accumulation in seeds. Accordingly, we selected candidate genes for the metabolic engineering of Camelina. Here we targeted the overexpression of Camelina PDCT gene, which encodes the phosphatidylcholine: diacylglycerol cholinephosphotransferase enzyme. PDCT is proposed as a gatekeeper responsible for the interconversions of diacylglycerol (DAG) and phosphatidylcholine (PC) pools and has the potential to increase the levels of TAG in seeds. To confirm whether increased CsPDCT activity in developing Camelina seeds would enhance carbon flux toward increased levels of TAG and alter oil composition, we overexpressed the CsPDCT gene under the control of the seed-specific phaseolin promoter. Camelina transgenics exhibited significant increases in seed yield (19-56%), seed oil content (9-13%), oil yields per plant (32-76%), and altered polyunsaturated fatty acid (PUFA) content compared to their parental wild-type (WT) plants. Results from [14C] acetate labeling of Camelina developing embryos expressing CsPDCT in culture indicated increased rates of radiolabeled fatty acid incorporation into glycerolipids (up to 64%, 59%, and 43% higher in TAG, DAG, and PC, respectively), relative to WT embryos. We conclude that overexpression of PDCT appears to be a positive strategy to achieve a synergistic effect on the flux through the TAG synthesis pathway, thereby further increasing oil yields in Camelina.

Lipid Metabolism and Improvement in Oilseed Crops: Recent Advances in Multi-Omics Studies

Oilseed crops are rich in plant lipids that not only provide essential fatty acids for the human diet but also play important roles as major sources of biofuels and indispensable raw materials for the chemical industry. The regulation of lipid metabolism genes is a major factor affecting oil production. In this review, we systematically summarize the metabolic pathways related to lipid production and storage in plants and highlight key research advances in characterizing the genes and regulatory factors influencing lipid anabolic metabolism. In addition, we integrate the latest results from multi-omics studies on lipid metabolism to provide a reference to better understand the molecular mechanisms underlying oil anabolism in oilseed crops.

Diacylglycerol acyltransferase (DGAT) in Crangon crangon and Pandalus montagui (Decapoda, Caridea) - Implications for lipid storage capacities and life history traits

Lipids play essential roles in cell-structuring, cell-signaling, and as efficient metabolic energy stores. Lipid storage capacities determine life history traits of organisms and, thus, their ecological function. Among storage lipids, triacylglycerols (TAGs) are widespread in marine invertebrates. However, abilities to accumulate TAGs can vary even between closely related species, such as the caridean shrimps Crangon crangon and Pandalus montagui. The first species shows low TAG levels throughout the year in the main storage organ, the midgut gland, while the latter accumulates high TAG-levels, peaking in summer. TAGs synthesis is facilitated by the terminal step of the Kennedy-pathway, where the enzyme diacylglycerol-acyltransferase (DGAT) catalyzes the esterification of diacylglycerols with activated fatty acids. We investigated DGAT activity in the midgut gland using a fluorescent enzyme assay. Sequence information was extracted from whole transcriptome shotgun assembly data, that is publicly available on NCBI, and catalytic properties were deduced from molecular structure analysis. C. crangon showed significantly lower TAG synthesis rates than P. montagui, which explains the native TAG levels. Transcriptome data yielded several isoforms of DGAT enzymes in both species. C. crangon DGAT showed point mutations, which are capable of obstructing the catalytic capacity. The consequences are limited starvation resistance and, thus, presumably restricting C. crangon to a habitat with year-round sufficient food. In contrast, higher TAG synthesis rates presumably enable P. montagui to extend into northern subarctic habitats with limited food availability in winter. Moreover, the limited TAG synthesis and accumulation in the midgut gland may force C. crangon to direct energy into the ovaries, which results in multiple spawnings.

Genetic and Morpho-Physiological Differences among Transgenic and No-Transgenic Cotton Cultivars

Three carbon-chain extension genes associated with fatty acid synthesis in upland cotton (Gossypium hirsutum), namely GhKAR, GhHAD, and GhENR, play important roles in oil accumulation in cotton seeds. In the present study, these three genes were cloned and characterized. The expression patterns of GhKAR, GhHAD, and GhENR in the high seed oil content cultivars 10H1014 and 10H1041 differed somewhat compared with those of 10H1007 and 2074B with low seed oil content at different stages of seed development. GhKAR showed all three cultivars showed higher transcript levels than that of 2074B at 10-, 40-, and 45-days post anthesis (DPA). The expression pattern of GhHAD showed a lower transcript level than that of 2074B at both 10 and 30 DPA but a higher transcript level than that of 2074B at 40 DPA. GhENR showed a lower transcript level than that of 2074B at both 15 and 30 DPA. The highest transcript levels of GhKAR and GhENR were detected at 15 DPA in 10H1007, 10H1014, and 10H1041 compared with 2074B. From 5 to 45 DPA cotton seed, the oil content accumulated continuously in the developing seed. Oil accumulation reached a peak between 40 DPA and 45 DPA and slightly decreased in mature seed. In addition, GhKAR and GhENR showed different expression patterns in fiber and ovule development processes, in which they showed high expression levels at 20 DPA during the fiber elongation stage, but their expression level peaked at 15 DPA during ovule development processes. These two genes showed the lowest expression levels at the late seed maturation stage, while GhHAD showed a peak of 10 DPA in fiber development. Compared to 2074B, the oil contents of GhKAR and GhENR overexpression lines increased 1.05~1.08 folds. These results indicated that GhHAD, GhENR, and GhKAR were involved in both seed oil synthesis and fiber elongation with dual biological functions in cotton.

Metabolic and transcriptomic study of pennycress natural variation identifies targets for oil improvement

Pennycress (Thlaspi arvense L.), a member of the Brassicaceae family, produces seed oil high in erucic acid, suitable for biodiesel and aviation fuel. Although pennycress, a winter annual, could be grown as a dedicated bioenergy crop, an increase in its seed oil content is required to improve its economic competitiveness. The success of crop improvement relies upon finding the right combination of biomarkers and targets, and the best genetic engineering and/or breeding strategies. In this work, we combined biomass composition with metabolomic and transcriptomic studies of developing embryos from 22 pennycress natural variants to identify targets for oil improvement. The selected accession collection presented diverse levels of fatty acids at maturity ranging from 29% to 41%. Pearson correlation analyses, weighted gene co-expression network analysis and biomarker identifications were used as complementary approaches to detect associations between metabolite level or gene expression and oil content at maturity. The results indicated that improving seed oil content can lead to a concomitant increase in the proportion of erucic acid without affecting the weight of embryos. Processes, such as carbon partitioning towards the chloroplast, lipid metabolism, photosynthesis, and a tight control of nitrogen availability, were found to be key for oil improvement in pennycress. Besides identifying specific targets, our results also provide guidance regarding the best timing for their modification, early or middle maturation. Thus, this work lays out promising strategies, specific for pennycress, to accelerate the successful development of lines with increased seed oil content for biofuel applications.

Integrated lipidomic and transcriptomic analysis reveals diacylglycerol accumulation in olive of Longnan (China)

Background

Olive (Olea europaea L.) oil accumulate more diacylglycerols (DAG) than mostly vegetable oils. Unsaturated fatty acids-enriched DAG consumption enhanced wellness in subjects. However, the mechanism of DAG accumulation is not yet fully understood.

Methods

In this study, gene network of DAG accumulation and fatty acid composition in the two olive mesocarps ("Chenggu 32" (CG) and "Koroneiki" (QJ)) were investigated by integrating lipidome and transcriptome techniques.

Results

A total of 1,408 lipid molecules were identified by lipidomic analysis in olive mesocarp, of which DAG (DAG36:3, DAG36:4 and DAG36:5) showed higher content, and triacylglycerols (TAG54:3, TAG54:4) exhibited opposite trend in CG. Specifically, DAG was rich in polyunsaturated fatty acids (especially C18:2) at the sn-2 position, which was inconsistent with TAG at the same positions (Primarily C18:1). Transcriptomic analysis revealed that phospholipase C (NPC, EC 3.1.4.3) were up-regulated relative to QJ, whereas diacylglycerol kinase (ATP) (DGK, EC 2.7.1.107), diacylglycerol acyltransferase (DGAT, EC 2.3.1.20), and phospholipid: diacylglycerol acyltransferase (PDAT, EC 2.3.1.158) were down-regulated.

Conclusion

We speculated that the non-acyl coenzyme A pathway played a significant role in DAG biosynthesis. Additionally, fatty acyl-ACP thioesterase B (FATB, EC 3.1.2.14), stearoyl [acyl-carrier-protein] 9-desaturase (SAD, EC 1.14.19.2) and omega-6 fatty acid desaturase (FAD2, EC 1.14.19.6) were highly expressed in CG and may be involved in regulating fatty acid composition. Meanwhile, phospholipase A1 (LCAT, EC 3.1.1.32) involved in the acyl editing reaction facilitated PUFA linkage at the sn-2 position of DAG. Our findings provide novel insights to increase the DAG content, improve the fatty acid composition of olive oil, and identify candidate genes for the production of DAG-rich oils.

Phospholipid:diacylglycerol acyltransferase1-overexpression stimulates lipid turnover, oil production and fitness in cold-grown plants

BACKGROUND

Extensive population growth and climate change accelerate the search for alternative ways of plant-based biomass, biofuel and feed production. Here, we focus on hitherto unknow, new promising cold-stimulated function of phospholipid:diacylglycerol acyltransferase1 (PDAT1) - an enzyme catalyzing the last step of triacylglycerol (TAG) biosynthesis.

RESULT

Overexpression of AtPDAT1 boosted seed yield by 160% in Arabidopsis plants exposed to long-term cold compared to standard conditions. Such seeds increased both their weight and acyl-lipids content. This work also elucidates PDAT1's role in leaves, which was previously unclear. Aerial parts of AtPDAT1-overexpressing plants were characterized by accelerated growth at early and vegetative stages of development and by biomass weighing three times more than control. Overexpression of PDAT1 increased the expression of SUGAR-DEPENDENT1 (SDP1) TAG lipase and enhanced lipid remodeling, driving lipid turnover and influencing biomass increment. This effect was especially pronounced in cold conditions, where the elevated synergistic expression of PDAT1 and SDP1 resulted in double biomass increase compared to standard conditions. Elevated phospholipid remodeling also enhanced autophagy flux in AtPDAT1-overexpresing lines subjected to cold, despite the overall diminished autophagy intensity in cold conditions.

CONCLUSIONS

Our data suggest that PDAT1 promotes greater vitality in cold-exposed plants, stimulates their longevity and boosts oilseed oil production at low temperature.

Genome-wide identification and expression of monoacylglycerol lipase (MAGL) gene family in peanut (Arachis hypogaea L.) and functional analysis of AhMGATs in neutral lipid metabolism

Monoacylglycerol lipase (MAGL) involved in regulating plant growth and development and stress responses, hydrolyzes monoacylglycerol (MAG) into free fatty acid and glycerol, which is the last step of triacylglycerol (TAG) breakdown. Here, a genome-wide characterization of MAGL gene family from cultivated peanut (Arachis hypogaea L.) was performed. In total, 24 MAGL genes were identified and unevenly distributed on 14 chromosomes, encoding 229-414 amino acids with molecular weights ranging from 25.91 to 47.01 kDa. Spatiotemporal and stress-induced expression was analyzed by qRT-PCR. Multiple sequence alignment revealed that AhMAGL1a/b and AhMAGL3a/b were the only four bifunctional enzymes with conserved regions of hydrolase and acyltransferase, which could also be named as AhMGATs. GUS histochemical assay showed that AhMAGL1a and -1b were strongly expressed in all tissues of the plants; whereas both AhMAGL3a and -3b were weakly expressed in plants. Subcellular localization analysis indicated that AhMGATs were localized in the endoplasmic reticulum and/or Golgi complex. Seed-specific overexpression of AhMGATs in Arabidopsis decreased the oil content of the seeds and altered the fatty acid compositions, indicating that AhMGATs were involved in TAG breakdown but not TAG biosynthesis in plant seeds. This study lays the foundation for better understanding AhMAGL genes biological function in planta.

The genomes of Vischeria oleaginous microalgae shed light on the molecular basis of hyper-accumulation of lipids

BACKGROUND

With the urgent need to reduce carbon emissions, and the dwindling reserves of easily exploitable fossil fuel, microalgae-based biofuels that can be used for transport systems and CO₂ abatement have attracted great attention worldwide in recent years. One useful characteristic of microalgae is their ability to accumulate high levels of lipid content, in particular under conditions of nitrogen deprivation, with numerous species identified so far. However, a trade-off between levels of lipid accumulation and biomass productivity hinders the commercial applicability of lipids from microalgae. Here, we sequenced the genomes of Vischeria sp. CAUP H4302 and Vischeria stellata SAG 33.83, which can accumulate high content of lipids rich in nutraceutical fatty acids and with excellent biomass yield in nitrogen-limiting culture.

RESULTS

A whole-genome duplication (WGD) event was revealed in V. sp. CAUP H4302, which is a rare event in unicellular microalgae. Comparative genomic analyses showed that a battery of genes encoding pivotal enzymes involved in fatty acids and triacylglycerol biosynthesis, storage polysaccharide hydrolysis, and nitrogen and amino acid-related metabolisms are expanded in the genus Vischeria or only in V. sp. CAUP H4302. The most highlighted is the expansion of cyanate lyase genes in the genus Vischeria, which may enhance their detoxification ability against the toxic cyanate by decomposing cyanate to NH₃ and CO₂, especially under nitrogen-limiting conditions, resulting in better growth performance and sustained accumulation of biomass under the aforementioned stress conditions.

CONCLUSIONS

This study presents a WGD event in microalgae, providing new insights into the genetic and regulatory mechanism underpinning hyper-accumulation of lipids and offering potentially valuable targets for future improvements in oleaginous microalgae by metabolic engineering.

Combined analysis of the metabolome and transcriptome provides insight into seed oil accumulation in soybean

BACKGROUND

Soybean (Glycine max (L.) Merr) is an important source of human food, animal feed, and bio-energy. Although the genetic network of lipid metabolism is clear in Arabidopsis, the understanding of lipid metabolism in soybean is limited.

RESULTS

In this study, 30 soybean varieties were subjected to transcriptome and metabolome analysis. In total, 98 lipid-related metabolites were identified, including glycerophospholipid, alpha-linolenic acid, linoleic acid, glycolysis, pyruvate, and the sphingolipid pathway. Of these, glycerophospholipid pathway metabolites accounted for the majority of total lipids. Combining the transcriptomic and metabolomic analyses, we found that 33 lipid-related metabolites and 83 lipid-related genes, 14 lipid-related metabolites and 17 lipid-related genes, and 12 lipid-related metabolites and 25 lipid-related genes were significantly correlated in FHO (five high-oil varieties) vs. FLO (five low-oil varieties), THO (10 high-oil varieties) vs. TLO (10 low-oil varieties), and HO (15 high-oil varieties) vs. LO (15 low-oil varieties), respectively.

CONCLUSIONS

The GmGAPDH and GmGPAT genes were significantly correlated with lipid metabolism genes, and the result revealed the regulatory relationship between glycolysis and oil synthesis. These results improve our understanding of the regulatory mechanism of soybean seed oil improvement.

Dynamic Regulation of Lipid Droplet Biogenesis in Plant Cells and Proteins Involved in the Process

Lipid droplets (LDs) are ubiquitous, dynamic organelles found in almost all organisms, including animals, protists, plants and prokaryotes. The cell biology of LDs, especially biogenesis, has attracted increasing attention in recent decades because of their important role in cellular lipid metabolism and other newly identified processes. Emerging evidence suggests that LD biogenesis is a highly coordinated and stepwise process in animals and yeasts, occurring at specific sites of the endoplasmic reticulum (ER) that are defined by both evolutionarily conserved and organism- and cell type-specific LD lipids and proteins. In plants, understanding of the mechanistic details of LD formation is elusive as many questions remain. In some ways LD biogenesis differs between plants and animals. Several homologous proteins involved in the regulation of animal LD formation in plants have been identified. We try to describe how these proteins are synthesized, transported to the ER and specifically targeted to LD, and how these proteins participate in the regulation of LD biogenesis. Here, we review current work on the molecular processes that control LD formation in plant cells and highlight the proteins that govern this process, hoping to provide useful clues for future research.

The genome of Orychophragmus violaceus provides genomic insights into the evolution of Brassicaceae polyploidization and its distinct traits

Orychophragmus violaceus, referred to as "eryuelan" (February orchid) in China, is an early-flowering ornamental plant. The high oil content and abundance of unsaturated fatty acids in O. violaceus seeds make it a potential high-quality oilseed crop. Here, we generated a whole-genome assembly for O. violaceus using Nanopore and Hi-C sequencing technologies. The assembled genome of O. violaceus was ∼1.3 Gb in size, with 12 pairs of chromosomes. Through investigation of ancestral genome evolution, we determined that the genome of O. violaceus experienced a tetraploidization event from a diploid progenitor with the translocated proto-Calepineae karyotype. Comparisons between the reconstructed subgenomes of O. violaceus identified indicators of subgenome dominance, indicating that subgenomes likely originated via allotetraploidy. O. violaceus was phylogenetically close to the Brassica genus, and tetraploidy in O. violaceus occurred approximately 8.57 million years ago, close in time to the whole-genome triplication of Brassica that likely arose via an intermediate tetraploid lineage. However, the tetraploidization in Orychophragmus was independent of the hexaploidization in Brassica, as evidenced by the results from detailed phylogenetic analyses and comparisons of the break and fusion points of ancestral genomic blocks. Moreover, identification of multi-copy genes regulating the production of high-quality oil highlighted the contributions of both tetraploidization and tandem duplication to functional innovation in O. violaceus. These findings provide novel insights into the polyploidization evolution of plant species and will promote both functional genomic studies and domestication/breeding efforts in O. violaceus.

The PRK/Rubisco shunt strongly influences Arabidopsis seed metabolism and oil accumulation, affecting more than carbon recycling

The carbon efficiency of storage lipid biosynthesis from imported sucrose in green Brassicaceae seeds is proposed to be enhanced by the PRK/Rubisco shunt, in which ribulose 1,5-bisphosphate carboxylase/oxygenase (Rubisco) acts outside the context of the Calvin-Benson-Bassham cycle to recycle CO2 molecules released during fatty acid synthesis. This pathway utilizes metabolites generated by the nonoxidative steps of the pentose phosphate pathway. Photosynthesis provides energy for reactions such as the phosphorylation of ribulose 5-phosphate by phosphoribulokinase (PRK). Here, we show that loss of PRK in Arabidopsis thaliana (Arabidopsis) blocks photoautotrophic growth and is seedling-lethal. However, seeds containing prk embryos develop normally, allowing us to use genetics to assess the importance of the PRK/Rubisco shunt. Compared with nonmutant siblings, prk embryos produce one-third less lipids-a greater reduction than expected from simply blocking the proposed PRK/Rubisco shunt. However, developing prk seeds are also chlorotic and have elevated starch contents compared with their siblings, indicative of secondary effects. Overexpressing PRK did not increase embryo lipid content, but metabolite profiling suggested that Rubisco activity becomes limiting. Overall, our findings show that the PRK/Rubisco shunt is tightly integrated into the carbon metabolism of green Arabidopsis seeds, and that its manipulation affects seed glycolysis, starch metabolism, and photosynthesis.

Changes in the content of pollen total lipid and TAG in Arabidopsis thaliana DGAT1 mutant as11

In mature pollen grains, lipids are primarily stored in the form of lipid droplets that provide energy and act as a carbon source for normal pollen development and germination. Triacylglycerol (TAG) is the major form of stored plant lipids. Diacylglycerol transferase, which is encoded by DGAT1 in Arabidopsis thaliana, is an important enzyme regulating triacylglycerol synthesis. Within the seeds of the DGAT1 mutant as11, the content of TAG is significantly decreased and the fatty acid composition also differs from the wild type. Transcriptome data of mature anthers showed that the genes involved in the TAG synthesis pathway were downregulated in as11. Analysis of gene expression patterns via transcriptome data also revealed that the expression of PDAT1, which functions in a manner complementary to the DGAT1 gene, was significantly decreased in as11, whereas the amylopectin synthase genes SS1 and SS2 were upregulated in mutant as11. We also detected lower total lipid, TAG and fatty acid contents in mature as11 pollen, with palmitic acid (C16:0) and linolenic acid (C18:3) being the major fatty acids in mature pollen. The cytological results showed that the lipid droplet content was reduced in mature as11 pollen. In the binuclear pollen grain II stage, WT pollen contained lipid droplets that were primarily accumulated around the generative nucleus, whereas the pollen in the mutant as11 was rich in starch grains that were primarily distributed around the vegetative nucleus. Ultrastructural analysis indicated that during pollen development in as11, the amount of endoplasmic reticulum in tapetal cells and pollen grains decreased, whereas the Golgi body content increased, which directly or indirectly led to a decrease in the levels of lipidosomes and an increase in the starch content in as11. Changes in the lipid content and fatty acid composition of the mutant as11 differ from those in the wild type during pollen development.

Acyl-CoA-dependent and acyl-CoA-independent avocado acyltransferases positively influence oleic acid content in nonseed triacylglycerols

In higher plants, acyl-CoA:diacylglycerol acyltransferase (DGAT) and phospholipid:diacylglycerol acyltransferase (PDAT) catalyze the terminal step of triacylglycerol (TAG) synthesis in acyl-CoA-dependent and -independent pathways, respectively. Avocado (Persea americana) mesocarp, a nonseed tissue, accumulates significant amounts of TAG (~70% by dry weight) that is rich in heart-healthy oleic acid (18:1). The oil accumulation stages of avocado mesocarp development coincide with high expression levels for type-1 DGAT (DGAT1) and PDAT1, although type-2 DGAT (DGAT2) expression remains low. The strong preference for oleic acid demonstrated by the avocado mesocarp TAG biosynthetic machinery represents lucrative biotechnological opportunities, yet functional characterization of these three acyltransferases has not been explored to date. We expressed avocado PaDGAT1, PaDGAT2, and PaPDAT1 in bakers' yeast and leaves of Nicotiana benthamiana. PaDGAT1 complemented the TAG biosynthesis deficiency in the quadruple mutant yeast strain H1246, and substantially elevated total cellular lipid content. In vitro enzyme assays showed that PaDGAT1 prefers oleic acid compared to palmitic acid (16:0). Both PaDGAT1 and PaPDAT1 increased the lipid content and elevated oleic acid levels when expressed independently or together, transiently in N. benthamiana leaves. These results indicate that PaDGAT1 and PaPDAT1 prefer oleate-containing substrates, and their coordinated expression likely contributes to sustained TAG synthesis that is enriched in oleic acid. This study establishes a knowledge base for future metabolic engineering studies focused on exploitation of the biochemical properties of PaDGAT1 and PaPDAT1.

Genome-wide identification and expression analysis of diacylglycerol acyltransferase genes in soybean (Glycine max)

Background

Soybean (Glycine max) is a major protein and vegetable oil source. In plants, diacylglycerol acyltransferase (DGAT) can exert strong flux control, which is rate-limiting for triacylglycerol biosynthesis in seed oil formation.

Methods

Here, we identified soybean DGAT genes via a bioinformatics method, thereby laying a solid foundation for further research on their function. Based on our bioinformatics analyses, including gene structure, protein domain characteristics, and phylogenetic analysis, 26 DGAT putative gene family members unevenly distributed on 12 of the 20 soybean chromosomes were identified and divided into the following four groups: DGAT1, DGAT2, WS/DGAT, and cytoplasmic DGAT.

Results

The Ka/Ks ratio of most of these genes indicated a significant positive selection pressure. DGAT genes exhibited characteristic expression patterns in soybean tissues. The differences in the structure and expression of soybean DGAT genes revealed the diversity of their functions and the complexity of soybean fatty acid metabolism. Our findings provide important information for research on the fatty acid metabolism pathway in soybean. Furthermore, our results will help identify candidate genes for potential fatty acid-profile modifications to improve soybean seed oil content.

Conclusions

This is the first time that in silico studies have been used to report the genomic and proteomic characteristics of DGAT in soybean and the effect of its specific expression on organs, age, and stages.

Genome-wide analysis of CtNF-YB and lipid synthesis regulation of CtNF-YB12 in Carthamus tinctorius L

The nuclear Factor YB of Carthamus tinctorius L. increased the content of unsaturated fatty acids by regulating the expression of genes involved in fatty acid synthesis and oil accumulation. Safflower (Carthamus tinctorius L.) seed oil is rich in linoleic acid and is widely used in food and medicine. Therefore, key genes regulating oil synthesis were mined through genetic engineering to provide genetic resources for improving oil content. Based on the conserved domain of the NF-YB, we screened and identified 14 CtNF-YB transcription factors in the safflower genome and divided them into three subfamilies through phylogenetic analysis. Regulatory motif analysis of the CtNF-YB promoter revealed specific cis-regulatory elements related to abiotic stress, growth, and development. Expression analysis of CtNF-YB family genes showed that non-Leafy Cotyledon 1(non-LEC1) genes were highly expressed in roots, leaves, and flowers; Leafy Cotyledon 1(LEC1) genes were highly expressed during early seed development; and Dr1-like genes were highly expressed in roots, stems, and leaves. CtNF-YB12 was identified as a LEC1 transcription factor based on phylogeny and BLAST alignment. Heterologous CtNF-YB12 expression in Arabidopsis thaliana increased seed pod length and seed size. Moreover, CtNF-YB12 overexpression increased the oil content of seeds, upregulated genes involved in fatty acid biosynthesis and glycolysis, and altered the content of unsaturated fatty acids, including oleic acid (C18:1), linoleic acid (C18:2), and linolenic acid (C18:3), as well as of sucrose, fructose, and glucose. CtNF-YB12 may increase the oil content by regulating key enzyme genes of oil synthesis, so it can be used as a reliable target.

The core triacylglycerol toolbox in woody oil plants reveals targets for oil production bioengineering

Woody oil plants are the most productive oil-bearing species that produce seeds with high levels of valuable triacylglycerols (TAGs). TAGs and their derivatives are the raw materials for many macromolecular bio-based products, such as nylon precursors, and biomass-based diesel. Here, we identified 280 genes encoding seven distinct classes of enzymes (i.e., G3PAT, LPAAT, PAP, DGAT, PDCT, PDAT, and CPT) involved in TAGs-biosynthesis. Several multigene families are expanded by large-scale duplication events, such as G3PATs, and PAPs. RNA-seq was used to survey the expression profiles of these TAG pathway-related genes in different tissues or development, indicating functional redundancy for some duplicated genes originated from the large-scale duplication events, and neo-functionalization or sub-functionalization for some of them. Sixty-two genes showed strong, preferential expression during the period of rapid seed lipid synthesis, suggesting that their might represented the core TAG-toolbox. We also revealed for the first time that there is no PDCT pathway in Vernicia fordii and Xanthoceras sorbifolium. The identification of key genes involved in lipid biosynthesis will be the foundation to plan strategies to develop woody oil plant varieties with enhanced processing properties and high oil content.

Pyruvate transporter BnaBASS2 impacts seed oil accumulation in Brassica napus

Bile acid: sodium symporter family protein 2 (BASS2) is a sodium-dependent pyruvate transporter, which transports pyruvate from cytosol into plastid in plants. In this study, we investigated the function of chloroplast envelope membrane-localized BnaBASS2 in seed metabolism and seed oil accumulation of Brassica napus (B. napus). Four BASS2 genes were identified in the genome of B. napus. BnaA05.BASS2 was overexpressed while BnaA05.BASS2 and BnaC04.BASS2-1 were mutated by CRISPR in B. napus. Metabolite analysis revealed that the manipulation of BnaBASS2 caused significant changes in glycolysis-, fatty acid synthesis-, and energy-related metabolites in the chloroplasts of 31 day-after-flowering (DAF) seeds. The analysis of fatty acids and lipids in developing seeds showed that BnaBASS2 could affect lipid metabolism and oil accumulation in developing seeds. Moreover, the overexpression (OE) of BnaA05.BASS2 could promote the expression level of multiple genes involved in the synthesis of oil and the formation of oil body during seed development. Disruption of BnaA05.BASS2 and BnaC04.BASS2-1 resulted in decreasing the seed oil content (SOC) by 2.8%-5.0%, while OE of BnaA05.BASS2 significantly promoted the SOC by 1.4%-3.4%. Together, our results suggest that BnaBASS2 is a potential target gene for breeding B. napus with high SOC.

Diacylglycerol Acyltransferase 3(DGAT3) Is Responsible for the Biosynthesis of Unsaturated Fatty Acids in Vegetative Organs of Paeonia rockii

'Diacylglycerol acyltransferase (DGAT)' acts as a key rate-limiting enzyme that catalyzes the final step of the de novo biosynthesis of triacylglycerol (TAG). The study was to characterize the function of the DGAT3 gene in Paeonia rockii, which is known for its accumulation of high levels of unsaturated fatty acids (UFAs). We identified a DGAT3 gene which encodes a soluble protein that is located within the chloroplasts of P. rockii. Functional complementarity experiments in yeast demonstrated that PrDGAT3 restored TAG synthesis. Linoleic acid (LA, C18:2) and α-linolenic acid (ALA, C18:3) are essential unsaturated fatty acids that cannot be synthesized by the human body. Through the yeast lipotoxicity test, we found that the yeast cell density was largely increased by adding exogenous LA and, especially, ALA to the yeast medium. Further ectopic transient overexpression in Nicotiana benthamiana leaf tissue and stable overexpression in Arabidopsis thaliana indicated that PrDGAT3 significantly enhanced the accumulation of the TAG and UFAs. In contrast, we observed a significant decrease in the total fatty acid content and in several major fatty acids in PrDGAT3-silenced tree peony leaves. Overall, PrDGAT3 is important in catalyzing TAG synthesis, with a substrate preference for UFAs, especially LA and ALA. These results suggest that PrDGAT3 may have practical applications in improving plant lipid nutrition and increasing oil production in plants.

Longer Duration of Active Oil Biosynthesis during Seed Development Is Crucial for High Oil Yield-Lessons from Genome-Wide In Silico Mining and RNA-Seq Validation in Sesame

Sesame, one of the ancient oil crops, is an important oilseed due to its nutritionally rich seeds with high protein content. Genomic scale information for sesame has become available in the public databases in recent years. The genes and their families involved in oil biosynthesis in sesame are less studied than in other oilseed crops. Therefore, we retrieved a total of 69 genes and their translated amino acid sequences, associated with gene families linked to the oil biosynthetic pathway. Genome-wide in silico mining helped identify key regulatory genes for oil biosynthesis, though the findings require functional validation. Comparing sequences of the SiSAD (stearoyl-acyl carrier protein (ACP)-desaturase) coding genes with known SADs helped identify two SiSAD family members that may be palmitoyl-ACP-specific. Based on homology with lysophosphatidic acid acyltransferase (LPAAT) sequences, an uncharacterized gene has been identified as SiLPAAT1. Identified key regulatory genes associated with high oil content were also validated using publicly available transcriptome datasets of genotypes contrasting for oil content at different developmental stages. Our study provides evidence that a longer duration of active oil biosynthesis is crucial for high oil accumulation during seed development. This underscores the importance of early onset of oil biosynthesis in developing seeds. Up-regulating, identified key regulatory genes of oil biosynthesis during early onset of seed development, should help increase oil yields.

Lipidome analysis and characterization of Buglossoides arvensis acyltransferases that incorporate polyunsaturated fatty acids into triacylglycerols

Buglossoides arvensis is a burgeoning oilseed crop that contains an unique combination of ω-3 and ω-6 polyunsaturated fatty acids (PUFA), constituting ~80-85% of seed triacylglycerols (TAGs). To uncover the critical TAG biosynthetic pathways contributing for high PUFA accumulation, we performed lipidome of developing seeds and characterized acyltransferases involved in the final step of TAG biosynthesis. During seed development, distribution of lipid molecular species in individual lipid classes showed distinct patterns from an early-stage (6 days after flowering (DAF)) to the middle-stage (12 and 18 DAF) of oil biosynthesis. PUFA-containing TAG species drastically increased from 6 to 12 DAF. The expression profiles of key triacylglycerol biosynthesis genes and patterns of phosphatidylcholine, diacylglycerol and triacylglycerol molecular species during seed development were used to predict the contribution of diacylglycerol acyltransferases (DGAT1 and DGAT2) and phospholipid: diacylglycerol acyltransferases (PDAT1 and PDAT2) to PUFA-rich TAG biosynthesis. Our analysis suggests that DGATs play a crucial role in enriching TAGs with PUFA compared to PDATs. This was further confirmed by fatty acid feeding studies in yeast expressing acyltransferases. BaDGAT2 preferentially incorporated high amounts of PUFAs into TAG, compared to BaDGAT1. Our results provide insight into the molecular mechanisms of TAG accumulation in this plant and identify target genes for transgenic production of SDA in traditional oilseed crops.

Genome-wide analysis of DGAT gene family in Perilla frutescens and functional characterization of PfDGAT2-2 and PfDGAT3-1 in Arabidopsis

Diacylglycerol acyltransferase (DGAT) is the rate-limiting enzyme that catalyzes the final step in triacylglycerol biosynthesis, however, members of DGAT gene family of Perilla frutescens has not yet been identified and characterized. In this study, a total of 20 PfDGAT genes were identified from the genome of Perilla frutescens and were divided into four groups (PfDGAT1, PfDGAT2, PfDGAT3, PfWS/DGAT) according to their phylogenetic relationships. These were unevenly distributed across the 12 chromosomes. Sequence analysis revealed that PfDGAT members of the same subfamily have highly conserved gene structures, protein motifs and cis-acting elements in their promoters. Gene duplication analysis showed that random duplication and segmental duplication contributed to the expansion of the DGAT family in P. frutescens. RNA-seq and qRT-PCR analysis suggested that they may play a role in the growth and development of Perilla, especially in the accumulation of seed oil. Compared with the wild-type, seed length, width, and 1000-seed weight of transgenic PfDGAT2-2 and PfDGAT3-1 Arabidopsis were significantly increased, as well as the seed oil content increased by 7.36-15.83 %. Over-expression of PfDGAT2-2 could significantly increase the content of C18:3 and C20:1 in Arabidopsis, while over-expression of PfDGAT3-1 could significantly enhance the content of C18:2 and C18:3. In conclusion, in this study the characteristics and potential functions of the PfDGAT family members were elucidated. Our findings provided basic information for further functional studies and helped to increase the yield and quality of Perilla oil.

Genome-wide association studies and genomic selection assays made in a large sample of cacao (Theobroma cacao L.) germplasm reveal significant marker-trait associations and good predictive value for improving yield potential

A genome-wide association study (GWAS) was undertaken to unravel marker-trait associations (MTAs) between SNP markers and phenotypic traits. It involved a subset of 421 cacao accessions from the large and diverse collection conserved ex situ at the International Cocoa Genebank Trinidad. A Mixed Linear Model (MLM) in TASSEL was used for the GWAS and followed by confirmatory analyses using GAPIT FarmCPU. An average linkage disequilibrium (r2) of 0.10 at 5.2 Mb was found across several chromosomes. Seventeen significant (P ≤ 8.17 × 10-5 (-log10 (p) = 4.088)) MTAs of interest, including six that pertained to yield-related traits, were identified using TASSEL MLM. The latter accounted for 5 to 17% of the phenotypic variation expressed. The highly significant association (P ≤ 8.17 × 10-5) between seed length to width ratio and TcSNP 733 on chromosome 5 was verified with FarmCPU (P ≤ 1.12 × 10-8). Fourteen MTAs were common to both the TASSEL and FarmCPU models at P ≤ 0.003. The most significant yield-related MTAs involved seed number and seed length on chromosome 7 (P ≤ 1.15 × 10-14 and P ≤ 6.75 × 10-05, respectively) and seed number on chromosome 1 (P ≤ 2.38 × 10-05), based on the TASSEL MLM. It was noteworthy that seed length, seed length to width ratio and seed number were associated with markers at different loci, indicating their polygenic nature. Approximately 40 candidate genes that encode embryo and seed development, protein synthesis, carbohydrate transport and lipid biosynthesis and transport were identified in the flanking regions of the significantly associated SNPs and in linkage disequilibrium with them. A significant association of fruit surface anthocyanin intensity co-localised with MYB-related protein 308 on chromosome 4. Testing of a genomic selection approach revealed good predictive value (genomic estimated breeding values (GEBV)) for economic traits such as seed number (GEBV = 0.611), seed length (0.6199), seed width (0.5435), seed length to width ratio (0.5503), seed/cotyledon mass (0.6014) and ovule number (0.6325). The findings of this study could facilitate genomic selection and marker-assisted breeding of cacao thereby expediting improvement in the yield potential of cacao planting material.

Towards oilcane: preliminary field evaluation of metabolically engineered sugarcane with hyper-accumulation of triacylglycerol in vegetative tissues

We recently generated oilcane, a metabolically engineered sugarcane with hyper-accumulation of energy dense triacylglycerol in vegetative tissues. Refinement of this strategy in high biomass crops like sugarcane may result in elevated lipid yields that exceed traditional oilseed crops for biodiesel production. This is the first report of agronomic performance, stable co-expression of lipogenic factors, and TAG accumulation in transgenic sugarcane under field conditions. Co-expression of WRI1; DGAT1, OLE1, and RNAi suppression of PXA1 was stable during the 2-year field evaluation and resulted in TAG accumulation up to 4.4% of leaf DW. This TAG accumulation was 70-fold higher than in non-transgenic sugarcane and more than 2-fold higher than previously reported for the same line under greenhouse conditions. TAG accumulation correlated highest with the expression of WRI1. However, constitutive expression of WRI1 was negatively correlated with biomass accumulation. Transgenic lines without WRI1 expression accumulated TAG up to 1.6% of leaf DW and displayed no biomass yield penalty in the plant cane. These findings confirm sugarcane as a promising platform for the production of vegetative lipids and will be used to inform strategies to maximize future biomass and lipid yields. The main conclusion is that constitutive expression of WRI1 in combination with additional lipogenic factors (DGAT1-2, OLE1, PXA1) in sugarcane under field conditions leads to hyper-accumulation of TAG and reduces biomass yield.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-022-01333-5.

The nucleotide metabolome of germinating Arabidopsis thaliana seeds reveals a central role for thymidine phosphorylation in chloroplast development

Thymidylates are generated by several partially overlapping metabolic pathways in different subcellular locations. This interconnectedness complicates an understanding of how thymidylates are formed in vivo. Analyzing a comprehensive collection of mutants and double mutants on the phenotypic and metabolic level, we report the effect of de novo thymidylate synthesis, salvage of thymidine, and conversion of cytidylates to thymidylates on thymidylate homeostasis during seed germination and seedling establishment in Arabidopsis (Arabidopsis thaliana). During germination, the salvage of thymidine in organelles contributes predominantly to the thymidylate pools and a mutant lacking organellar (mitochondrial and plastidic) thymidine kinase has severely altered deoxyribonucleotide levels, less chloroplast DNA, and chlorotic cotyledons. This phenotype is aggravated when mitochondrial thymidylate de novo synthesis is additionally compromised. We also discovered an organellar deoxyuridine-triphosphate pyrophosphatase and show that its main function is not thymidylate synthesis but probably the removal of noncanonical nucleotide triphosphates. Interestingly, cytosolic thymidylate synthesis can only compensate defective organellar thymidine salvage in seedlings but not during germination. This study provides a comprehensive insight into the nucleotide metabolome of germinating seeds and demonstrates the unique role of enzymes that seem redundant at first glance.

An alternative angiosperm DGAT1 topology and potential motifs in the N-terminus

The highly variable cytoplasmic N-terminus of the plant diacylglycerol acyltransferase 1 (DGAT1) has been shown to have roles in oligomerization as well as allostery; however, the biological significance of the variation within this region is not understood. Comparing the coding sequences over the variable N-termini revealed the Poaceae DGAT1s contain relatively high GC compositional gradients as well as numerous direct and inverted repeats in this region. Using a variety of reciprocal chimeric DGAT1s from angiosperms we show that related N-termini had similar effects (positive or negative) on the accumulation of the recombinant protein in Saccharomyces cerevisiae. When expressed in Camelina sativa seeds the recombinant proteins of specific chimeras elevated total lipid content of the seeds as well as increased seed size. In addition, we combine N- and C-terminal as well as internal tags with high pH membrane reformation, protease protection and differential permeabilization. This led us to conclude the C-terminus is in the ER lumen; this contradicts earlier reports of the cytoplasmic location of plant DGAT1 C-termini.

24-Epibrassinolide Promotes Fatty Acid Accumulation and the Expression of Related Genes in Styrax tonkinensis Seeds

Styrax tonkinensis, whose seeds are rich in unsaturated fatty acids (UFAs), is a high oil value tree species, and the seed oil has perfect biodiesel properties. Therefore, the elucidation of the effect of 24-epibrassinolide (EBL) on fatty acid (FA) concentration and the expression of FA biosynthesis-related genes is critical for deeply studying the seed oil in S. tonkinensis. In this study, we aimed to investigate the changing trend of FA concentration and composition and identify candidate genes involved in FA biosynthesis under EBL treatment using transcriptome sequencing and GC-MS. The results showed that 5 μmol/L of EBL (EBL5) boosted the accumulation of FA and had the hugest effect on FA concentration at 70 days after flowering (DAF). A total of 20 FAs were identified; among them, palmitic acid, oleic acid, linoleic acid, and linolenic acid were the main components. In total, 117,904 unigenes were detected, and the average length was 1120 bp. Among them, 1205 unigenes were assigned to ‘lipid translations and metabolism’ in COG categories, while 290 unigenes were assigned to ‘biosynthesis of unsaturated fatty acid’ in KEGG categories. Twelve important genes related to FA biosynthesis were identified, and their expression levels were confirmed by quantitative real-time PCR. KAR, KASIII, and accA, encoding FA biosynthesis-related enzymes, all expressed the highest at 70 DAF, which was coincident with a rapid rise in FA concentration during seed development. FAD2 and FATB conduced to UFA and saturated fatty acids (SFA) accumulation, respectively. EBL5 induced the expression of FA biosynthesis-related genes. The concentration of FA was increased after EBL5 application, and EBL5 also enhanced the enzyme activity by promoting the expression of genes related to FA biosynthesis. Our research could provide a reference for understanding the FA biosynthesis of S. tonkinensis seeds at physiological and molecular levels.

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.

Expression of AtWRI1 and AtDGAT1 during soybean embryo development influences oil and carbohydrate metabolism

Soybean oil is one of the most consumed vegetable oils worldwide. Genetic improvement of its concentration in seeds has been historically pursued due to its direct association with its market value. Engineering attempts aiming to increase soybean seed oil presented different degrees of success that varied with the genetic design and the specific variety considered. Understanding the embryo's responses to the genetic modifications introduced, is a critical step to successful approaches. In this work, the metabolic and transcriptional responses to AtWRI1 and AtDGAT1 expression in soybean seeds were evaluated. AtWRI1 is a master regulator of fatty acid (FA) biosynthesis, and AtDGAT1 encodes an enzyme catalysing the final and rate-limiting step of triacylglycerides biosynthesis. The events expressing these genes in the embryo did not show an increase in total FA content, but they responded with changes in the oil and carbohydrate composition. Transcriptomic studies revealed a down-regulation of genes putatively encoding for oil body packaging proteins, and a strong induction of genes annotated as lipases and FA biosynthesis inhibitors. Novel putative AtWRI1 targets, presenting an AW-box in the upstream region of the genes, were identified by comparison with an event that harbours only AtWRI1. Lastly, targeted metabolomics analysis showed that carbon from sugar phosphates could be used for FA competing pathways, such as starch and cell wall polysaccharides, contributing to the restriction in oil accumulation. These results allowed the identification of key cellular processes that need to be considered to break the embryo's natural restriction to uncontrolled seed lipid increase.

Characterization of sucrose binding protein as a seed-specific promoter in transgenic tobacco Nicotiana tabacum L

Seed-specific expression using appropriate promoters is a recommended strategy for the efficiently producing valuable metabolites in transgenic plants. In the present study, we investigated the sequence of sucrose binding protein (SBP) as a seed-specific promoter to find the cis-acting elements specific to gene expression in seeds. The 1860 bp SBP sequence was analyzed using Plant Care and PLACE databases to find cis-acting elements, which resulted in a finding of 22 cis-acting elements required for seed expression. In addition, we have discovered cis- acting elements that are indirectly involved in triacylglycerol synthesis (GATABOX, DOFCOREZM, CACGTGMOTIF). The seed specificity of SBP was analyzed by generating a stable transgenic tobacco plant harboring β-glucuronidase (GUS) reporter gene under the control of the SBP promoter. Histochemical analysis of these transgenic tobacco plants indicated decreasing GUS activity in the leaves during the vegetative stage. However, the mature seeds of transgenic plants showed GUS activity. Moreover, the SBP promoter function in the seed oil content was evaluated by the expression of DGAT1. The expression analysis of DGAT1 in SBP-DGAT1 transgenic tobacco seeds using quantitative real-time PCR revealed a 7.8-fold increase in DGAT1 than in non-transgenic plants. Moreover, oil content increased up to 2.19 times more than in non-transgenic plants. And the oil content of the SBP-DGAT1 transgenic tobacco leaves did not change compared to the control plant. Therefore, we suggested that the SBP promoter could be used as a seed-specific promoter for targeted expression of desired genes in the metabolite engineering of oilseed crops.

Transcriptomic and Metabolomic Analysis Unravels the Molecular Regulatory Mechanism of Fatty Acid Biosynthesis in Styrax tonkinensis Seeds under Methyl Jasmonate Treatment

As the germ of a highly productive oil tree species, Styrax tonkinensis seeds have great potential to produce biodiesel and they have marvelous fatty acid (FA) composition. In order to explore the molecular regulatory mechanism of FA biosynthesis in S. tonkinensis seeds after methyl jasmonate (MJ) application, transcriptomic and metabolomic techniques were adopted so as to dissect the genes that are related to FA biosynthesis and their expression levels, as well as to discover the major FA concentration and composition. The results revealed that 200 μmol/L of MJ (MJ200) increased the crude fat (CF) mass fraction and generated the greatest impact on CF accumulation at 70 days after flowering. Twenty FAs were identified, among which palmitic acid, oleic acid, linoleic acid and linolenic acid were the major FAs, and the presence of MJ200 affected their concentrations variously. MJ200 could enhance FA accumulation through elevating the activity of enzymes that are related to FA synthesis. The number of differentially expressed genes increased with the seeds’ development in general. Fatty acid biosynthesis, the biosynthesis of unsaturated fatty acid, fatty acid elongation and glycerolipid metabolism were the main lipid metabolism pathways that were found to be involved. The changes in the expression levels of EAR, KAR, accA, accB and SAD2 were consistent with the changes in the CF mass fraction, indicating that they are important genes in the FA biosynthesis of S. tonkinensis seeds and that MJ200 promoted their expression levels. In addition, bZIP (which was screened by weighted correlation network analysis) also created significant impacts on FA biosynthesis. Our research has provided a basis for further studies on FA biosynthesis that is regulated by MJ200 at the molecular level and has helped to clarify the functions of key genes in the FA metabolic pathway in S. tonkinensis seeds.

Functional Characterization of Soybean Diacylglycerol Acyltransferase 3 in Yeast and Soybean

Diacylglycerol acyltransferases (DGAT) function as the key rate-limiting enzymes in de novo biosynthesis of triacylglycerol (TAG) by transferring an acyl group from acyl-CoA to sn-3 of diacylglycerol (DAG) to form TAG. Here, two members of the type 3 DGAT gene family, GmDGAT3-1 and GmDGAT3-2, were identified from the soybean (Glycine max) genome. Both of them were predicted to encode soluble cytosolic proteins containing the typical thioredoxin-like ferredoxin domain. Quantitative PCR analysis revealed that GmDGAT3-2 expression was much higher than GmDGAT3-1's in various soybean tissues such as leaves, flowers, and seeds. Functional complementation assay using TAG-deficient yeast (Saccharomyces cerevisiae) mutant H1246 demonstrated that GmDGAT3-2 fully restored TAG biosynthesis in the yeast and preferentially incorporated monounsaturated fatty acids (MUFAs), especially oleic acid (C18:1) into TAGs. This substrate specificity was further verified by fatty-acid feeding assays and in vitro enzyme activity characterization. Notably, transgenic tobacco (Nicotiana benthamiana) data showed that heterogeneous expression of GmDGAT3-2 resulted in a significant increase in seed oil and C18:1 levels but little change in contents of protein and starch compared to the EV-transformed tobacco plants. Taken together, GmDGAT3-2 displayed a strong enzymatic activity to catalyze TAG assembly with high substrate specificity for MUFAs, particularly C18:1, playing an important role in the cytosolic pathway of TAG synthesis in soybean. The present findings provide a scientific reference for improving oil yield and FA composition in soybean through gene modification, further expanding our knowledge of TAG biosynthesis and its regulatory mechanism in oilseeds.

Different acyl-CoA:diacylglycerol acyltransferases vary widely in function, and a targeted amino acid substitution enhances oil accumulation

Triacylglycerols (TAGs) are the major component of plant storage lipids such as oils. Acyl-CoA:diacylglycerol acyltransferase (DGAT) catalyzes the final step of the Kennedy pathway, and is mainly responsible for plant oil accumulation. We previously found that the activity of Vernonia DGAT1 was distinctively higher than that of Arabidopsis and soybean DGAT1 in a yeast microsome assay. In this study, the DGAT1 cDNAs of Arabidopsis, Vernonia, soybean, and castor bean were introduced into Arabidopsis. All Vernonia DGAT1-expressing lines showed a significantly higher oil content (49% mean increase compared with the wild-type) followed by soybean and castor bean. Most Arabidopsis DGAT1-overexpressing lines did not show a significant increase. In addition to these four DGAT1 genes, sunflower, Jatropha, and sesame DGAT1 genes were introduced into a TAG biosynthesis-defective yeast mutant. In the yeast expression culture, DGAT1s from Arabidopsis, castor bean, and soybean only slightly increased the TAG content; however, DGAT1s from Vernonia, sunflower, Jatropha, and sesame increased TAG content >10-fold more than the former three DGAT1s. Three amino acid residues were characteristically common in the latter four DGAT1s. Using soybean DGAT1, these amino acid substitutions were created by site-directed mutagenesis and substantially increased the TAG content.

Genome-Wide Characterization of DGATs and Their Expression Diversity Analysis in Response to Abiotic Stresses in Brassica napus

Triacylglycerol (TAG) is the most important storage lipid for oil plant seeds. Diacylglycerol acyltransferases (DGATs) are a key group of rate-limiting enzymes in the pathway of TAG biosynthesis. In plants, there are three types of DGATs, namely, DGAT1, DGAT2 and DGAT3. Brassica napus, an allotetraploid plant, is one of the most important oil plants in the world. Previous studies of Brassica napus DGATs (BnaDGATs) have mainly focused on BnaDGAT1s. In this study, four DGAT1s, four DGAT2s and two DGAT3s were identified and cloned from B. napus ZS11. The analyses of sequence identity, chromosomal location and collinearity, phylogenetic tree, exon/intron gene structures, conserved domains and motifs, and transmembrane domain (TMD) revealed that BnaDGAT1, BnaDGAT2 and BnaDGAT3 were derived from three different ancestors and shared little similarity in gene and protein structures. Overexpressing BnaDGATs showed that only four BnaDGAT1s can restore TAG synthesis in yeast H1246 and promote the accumulation of fatty acids in yeast H1246 and INVSc1, suggesting that the three BnaDGAT subfamilies had greater differentiation in function. Transcriptional analysis showed that the expression levels of BnaDGAT1s, BnaDGAT2s and BnaDGAT3s were different during plant development and under different stresses. In addition, analysis of fatty acid contents in roots, stems and leaves under abiotic stresses revealed that P starvation can promote the accumulation of fatty acids, but no obvious relationship was shown between the accumulation of fatty acids with the expression of BnaDGATs under P starvation. This study provides an extensive evaluation of BnaDGATs and a useful foundation for dissecting the functions of BnaDGATs in biochemical and physiological processes.

Heterologous Expression of Jatropha curcas Fatty Acyl-ACP Thioesterase A (JcFATA) and B (JcFATB) Affects Fatty Acid Accumulation and Promotes Plant Growth and Development in Arabidopsis

Plant fatty acyl-acyl carrier protein (ACP) thioesterases terminate the process of de novo fatty acid biosynthesis in plastids by hydrolyzing the acyl-ACP intermediates, and determine the chain length and levels of free fatty acids. They are of interest due to their roles in fatty acid synthesis and their potential to modify plant seed oils through biotechnology. Fatty acyl-ACP thioesterases (FAT) are divided into two families, i.e., FATA and FATB, according to their amino acid sequence and substrate specificity. The high oil content in Jatropha curcas L. seed has attracted global attention due to its potential for the production of biodiesel. However, the detailed effects of JcFATA and JcFATB on fatty acid biosynthesis and plant growth and development are still unclear. In this study, we found that JcFATB transcripts were detected in all tissues and organs examined, with especially high accumulation in the roots, leaves, flowers, and some stages of developing seeds, and JcFATA showed a very similar expression pattern. Subcellular localization of the JcFATA-GFP and JcFATB-GFP fusion protein in Arabidopsis leaf protoplasts showed that both JcFATA and JcFATB localized in chloroplasts. Heterologous expression of JcFATA and JcFATB in Arabidopsis thaliana individually generated transgenic plants with longer roots, stems and siliques, larger rosette leaves, and bigger seeds compared with those of the wild type, indicating the overall promotion effects of JcFATA and JcFATB on plant growth and development while JcFATB had a larger impact. Compositional analysis of seed oil revealed that all fatty acids except 22:0 were significantly increased in the mature seeds of JcFATA-transgenic Arabidopsis lines, especially unsaturated fatty acids, such as the predominant fatty acids of seed oil, 18:1, 18:2, and 18:3. In the mature seeds of the JcFATB-transgenic Arabidopsis lines, most fatty acids were increased compared with those in wild type too, especially saturated fatty acids, such as 16:0, 18:0, 20:0, and 22:0. Our results demonstrated the promotion effect of JcFATA and JcFATB on plant growth and development, and their possible utilization to modify the seed oil composition and content in higher plants.

An integrated omics analysis reveals the gene expression profiles of maize, castor bean, and rapeseed for seed oil biosynthesis

BACKGROUND

Seed storage lipids are valuable for human diet and for the sustainable development of mankind. In recent decades, many lipid metabolism genes and pathways have been identified, but the molecular mechanisms that underlie differences in seed oil biosynthesis in species with developed embryo and endosperm are not fully understood.

RESULTS

We performed comparative genome and transcriptome analyses of castor bean and rapeseed, which have high seed oil contents, and maize, which has a low seed oil content. These results revealed the molecular underpinnings of the low seed oil content in maize. First of all, transcriptome analyses showed that more than 61% of the lipid- and carbohydrate-related genes were regulated in castor bean and rapeseed, but only 20.1% of the lipid-related genes and 22.5% of the carbohydrate-related genes were regulated in maize. Then, compared to castor bean and rapeseed, fewer lipid biosynthesis genes but more lipid metabolism genes were regulated in the maize embryo. More importantly, most maize genes encoding lipid-related transcription factors, triacylglycerol (TAG) biosynthetic enzymes, pentose phosphate pathway (PPP) and Calvin Cycle proteins were not regulated during seed oil synthesis, despite the presence of many homologs in the maize genome. Additionally, we observed differential regulation of vital oil biosynthetic enzymes and extremely high expression levels of oil biosynthetic genes in castor bean, which were consistent with the rapid accumulation of oil in castor bean developing seeds.

CONCLUSIONS

Compared to high-oil seeds (castor bean and rapeseed), less oil biosynthetic genes were regulated during the seed development in low-oil seed (maize). These results shed light on molecular mechanisms of lipid biosynthesis in maize, castor bean, and rapeseed. They can provide information on key target genes that may be useful for future experimental manipulation of oil production in oil plants.

Proteomic and lipidomics analyses of high fatty acid AhDGAT3 transgenic soybean reveals the key lipase gene associated with the lipid internal mechanism

Vegetable oil is one of the most important components of human nutrition. Soybean (Glycine max) is an important oil crop worldwide and contains rich unsaturated fatty acids. Diacylglycerol acyltransferase (DGAT) is a key rate-limiting enzyme in the Kennedy pathway from diacylglycerol (DAG) to triacylglycerol (TAG). In this study, we conducted further research using T3 AhDGAT3 transgenic soybean. A high-performance gas chromatography flame ionization detector showed that oleic acid (18:1) content and total fatty acid content of transgenic soybean were significantly higher than those of the wild type (WT). However, linoleic acid (18:2) was much lower than that in the WT. For further mechanistic studies, 20 differentially expressed proteins (DEPs) and 119 differentially expressed metabolites (DEMs) were identified between WT (JACK) and AhDGAT3 transgenic soybean mature seeds using proteomic and lipidomics analyses. Combined proteomic and lipidomics analyses showed that the upregulation of the key DEP (lipase GDSL domain-containing protein) in lipid transport and metabolic process induced an increase in the total fatty acid and 18:1 composition, but a decrease in the 18:2 composition of fatty acids. Our study provides new insights into the deep study of molecular mechanism underlying the enhancement of fatty acids in transgenic soybeans, especially oleic acid and total fatty acid, which are enhanced by over-expression of AhDGAT3.

Effects of elevated air temperature coupling with soil drought on carbohydrate metabolism and oil synthesis during cottonseed development

Cotton, as the fifth-largest oilseed crop, often faces the coupling stress of heat and drought. Still, the effects of combined stress on cottonseed oil synthesis and its closely related carbon metabolism are poorly investigated. To this end, experiments were conducted with two cultivars (Sumian 15 and PHY370WR) under two temperature regimes: ambient temperature (AT) and elevated temperature (ET, which was 2.5°C-2.7°C higher than AT) and three water regimes: optimum soil moisture (soil relative water content [SRWC] at 75% ± 5%), and drought (SD) including SRWC 60% ± 5% and SRWC 45% ± 5%, during 2016-2018. Results showed that ET plus SD decreased cottonseed kernel yield, seed index, kernel weight, and kernel percentage more than either single stress. The content of hexoses, the carbon skeleton source for oil synthesis, was decreased by ET while increased by SD. The combined stress increased the hexose content by increasing the activities of sucrose synthase (SuSy, EC 2.4.1.13) and invertase (Inv, EC 3.2.1.26) and upregulating GhSuSy expression; however, hexose content under combined stress was lower than that under SD alone. Increased oil content under SD was attributed to the high phosphoenolpyruvate carboxylase (PEPCase, EC 4.1.1.31), acetyl-CoA carboxylase (ACCase, EC 6.4.1.2), and diacylglycerol acyltransferase (DGAT, EC 2.3.1.20) activities, whereas the opposite effects were seen under ET. Under combined stress, although ACCase activity decreased, PEPCase and DGAT activities, and GhPEPC-1 and GhDGAT-1 expression upregulated, enhancing carbon flow into oil metabolism and triacylglycerol synthesis, ultimately generating higher oil content.

Metabolic flux analysis of the non-transitory starch tradeoff for lipid production in mature tobacco leaves

The metabolic plasticity of tobacco leaves has been demonstrated via the generation of transgenic plants that can accumulate over 30% dry weight as triacylglycerols. In investigating the changes in carbon partitioning in these high lipid-producing (HLP) leaves, foliar lipids accumulated stepwise over development. Interestingly, non-transient starch was observed to accumulate with plant age in WT but not HLP leaves, with a drop in foliar starch concurrent with an increase in lipid content. The metabolic carbon tradeoff between starch and lipid was studied using 13CO2-labeling experiments and isotopically nonstationary metabolic flux analysis, not previously applied to the mature leaves of a crop. Fatty acid synthesis was investigated through assessment of acyl-acyl carrier proteins using a recently derived quantification method that was extended to accommodate isotopic labeling. Analysis of labeling patterns and flux modeling indicated the continued production of unlabeled starch, sucrose cycling, and a significant contribution of NADP-malic enzyme to plastidic pyruvate production for the production of lipids in HLP leaves, with the latter verified by enzyme activity assays. The results suggest an inherent capacity for a developmentally regulated carbon sink in tobacco leaves and may in part explain the uniquely successful leaf lipid engineering efforts in this crop.

Critical metabolic pathways and SAD/FADs, WRI1s, and DGATs cooperate for high-oleic acid oil production in developing oil tea (Camellia oleifera) seeds

Oil tea trees produce high-quality edible oils with desirably high oleic acid (18:1) and low linoleic (18:2) and linolenic (18:3) fatty acid (FA) levels, but limited understanding of tea oil biosynthesis and regulation has become a significant obstacle for the breeding of high-yield and -quality oil tea varieties. By integrating metabolite and transcriptome analyses of developing oil tea seeds, we dissected the critical metabolic pathways, including glycolysis, fatty acid, and triacylglycerol (TAG) biosynthesis, as well as genes essential for tea seed oil production. Two plastidic stearoyl-acyl carrier protein desaturases (CoSAD1 and 2) and two endoplasmic reticulum-localized FA desaturases (CoFAD2 and 3) were functionally characterized as responsible for high 18:1 and low 18:2 and 18:3 proportions in tea oils. Two diacylglycerol O-acyltransferases (CoDGAT1 and 2) that may prefer to synthesize 18:1-TAG were functionally characterized and might be also important for high 18:1-TAG production. The highly expressed CoWRI1a and b were identified and characterized as activators of glycolysis and regulators of directing source carbon flux into FA biosynthesis in developing oil tea seeds. The upregulated CoSADs with downregulated CoFAD2 and CoFAD3 at the late seed developmental stages mainly accounted for high 18:1 levels. Two CoDGATs might be responsible for assembling TAGs with oleoyl acyl chains, whilst two CoWRI1s regulated carbons from parental sources, partitioning into oil production in oil tea embryo sinks. This study provides a deep understanding of the biosynthesis of tea seed oils and information on genes that may be used as molecular markers to breed oil tea varieties with higher oil yield and quality.

Nontargeted metabolomic and multigene expression analyses reveal the mechanism of oil biosynthesis in sea buckthorn berry pulp rich in palmitoleic acid

Sea buckthorn berry pulp (SBP) oil is abundant in palmitoleic acid (C16:1). However, metabolic mechanisms of oil biosynthesis in SBP (non-seed tissues) are not clear. Thus, comparative nontargeted metabolomic analysis of the four developmental stages of berry pulp in two lines, Za56 and TF2-36, was performed. The results revealed that glycerol-3-phosphate (G3P) was critical for high oil accumulation in the mid-early developmental stages. In particular, the metabolism of phosphatidylcholine (PC) (16:0/16:0), PC (16:0/16:1), and PC (16:1/16:1) was also significantly altered. Sufficient supply of G3P and 16:1-CoA, coupled with upregulated expression of the glycerol-3-phosphate dehydrogenase (GPD1) and delta-9 desaturase (Δ9D) genes, were associated with high oil content enriched in C16:1 in SBP. Our results provide a scientific basis for the development of metabolic engineering strategies to increase the oil content in SBP with a high level of C16:1.