Regulation and structure of the heteromeric acetyl-CoA carboxylase

Effects of Portulaca Oleracea Extract on Acute Alcoholic Liver Injury of Rats

The present study was envisaged to investigate the chemical constituents and the intervention effects of Portulaca oleracea extract (POE) on acute alcoholic liver injury of rats. The chemical composition of POE was detected by high performance liquid chromatography (HPLC). Sixty male Wistar rats were divided into 6 groups: Normal control (NC) group, acute alcoholic liver injury model group (ALI), low, medium and high dose of POE (25, 50, 100 mg/kg) groups and bifendate (BF, 3.75 mg/kg) group. Each group was given by intragastrical administration for 7 days. Alcoholic liver injury was induced in the experimental model by administering 50% ethanol at 8 mL/kg and repeated administration after 6 h, for a period of 7 days. The results showed that pretreatment with POE significantly reduced the ethanol-elevated serum level of alanine aminotransferase (ALT), aspartate aminotransferase (AST), alkaline phosphatase (ALP) and triglyceride (TG). The activities of superoxide dismutase (SOD) and glutathione peroxidase (GSH-PX) in liver were enhanced followed by administration of POE, while the content of nitric oxide (NO) and malondialdehyde (MDA) was found to decrease. Hepatic content of tumor necrosis factor-α (TNF-α), and interleukin-6 (IL-6) was also reduced by POE treatment. These results indicated that POE could increase the antioxidant capacity and relieve the inflammatory injury of the liver cells induced by ethanol. Meanwhile, in our study, POE reduced the expression of miR-122, acetyl coenzyme A carboxylase (ACC) 1 mRNA and protein and increased the expression of lipoprotein lipase (LPL) mRNA and protein in liver, which indicated that POE could improve the lipid metabolism disorder induced by ethanol. Our findings suggested that POE had protective effects on acute alcoholic liver injury of rats.

Caracterización <i>in silico</i> y análisis de la expresión de la subunidad alfa de la acetil-coenzima a carboxilasa heteromérica de dos microalgas

Las microalgas son microorganismos fotosintéticos con gran potencial para abastecer las demandas energéticas mundiales. Sin embargo, los limitados conocimientos que se tienen de estos organismos, en particular a nivel molecular de los procesos metabólicos, han limitado su uso con estos propósitos. En esta investigación se ha realizado el análisis in silico de la subunidad alfa de la acetil-Coenzima A carboxilasa heteromérica (αACCasa), una enzima clave en la biosíntesis de lípidos de las microalgas Chlorella sp. y Scenedesmus sp. Asimismo, se ha medido la expresión de este gen en ambas especies cultivadas en medios deficientes de nitrógeno. Los resultados indican que la αACCasa muestra conservación estructural y funcional en ambas especies de microalgas y su mayor similitud genética con otras especies de microalgas. Asimismo, se ha mostrado que el nivel de expresión del gen se incrementa significativamente cuando las microalgas son cultivadas en ausencia de nitrógeno, lo cual se relaciona a su vez con una mayor acumulación de lípidos microalgales. En conclusión, el análisis in silico de la αACCasa de Chlorella sp. y Scenedesmus sp. presentan características estructurales, funcionales y evolutivas muy similares con otras especies de microalgas y plantas. Asimismo, el estudio revela que en ambas especies el gen se sobreexpresa cuando las microalgas son sometidas a estrés por deficiencia de nitrógeno, el cual se relaciona significativamente con la acumulación de lípidos totales en estas células.

Quantitative Proteomic Analysis of Low Linolenic Acid Transgenic Soybean Reveals Perturbations of Fatty Acid Metabolic Pathways

To understand the effect of fatty acid desaturase gene (GmFAD3) silencing on perturbation of fatty acid (FA) metabolic pathways, the changes are compared in protein profiling in control and low linolenic acid transgenic soybeans using tandem mass tag based mass spectrometry. Protein profiling of the transgenic line unveiled changes in several key enzymes of FA metabolism. This includes enzymes of lower abundance; fabH, fabF, and thioestrase associated with FA initiation, elongation, and desaturation processes and LOX1_5, ACOX, ACAA1, MFP2 associated with β-oxidation of α-linolenic acids pathways. In addition, the GmFAD3 silencing results in a significant reduction in one of the major allergens, Gly m 4 (C6T3L5). These results are important for exploring how plants adjust in their biological processes when certain changes are induced in the genetic makeup. A complete understanding of these processes will aid researchers to alter genes for developing value-added soybeans.

Chloroplast competition is controlled by lipid biosynthesis in evening primroses

In most eukaryotes, organellar genomes are transmitted preferentially by the mother, but molecular mechanisms and evolutionary forces underlying this fundamental biological principle are far from understood. It is believed that biparental inheritance promotes competition between the cytoplasmic organelles and allows the spread of so-called selfish cytoplasmic elements. Those can be, for example, fast-replicating or aggressive chloroplasts (plastids) that are incompatible with the hybrid nuclear genome and therefore maladaptive. Here we show that the ability of plastids to compete against each other is a metabolic phenotype determined by extremely rapidly evolving genes in the plastid genome of the evening primrose Oenothera Repeats in the regulatory region of accD (the plastid-encoded subunit of the acetyl-CoA carboxylase, which catalyzes the first and rate-limiting step of lipid biosynthesis), as well as in ycf2 (a giant reading frame of still unknown function), are responsible for the differences in competitive behavior of plastid genotypes. Polymorphisms in these genes influence lipid synthesis and most likely profiles of the plastid envelope membrane. These in turn determine plastid division and/or turnover rates and hence competitiveness. This work uncovers cytoplasmic drive loci controlling the outcome of biparental chloroplast transmission. Here, they define the mode of chloroplast inheritance, as plastid competitiveness can result in uniparental inheritance (through elimination of the "weak" plastid) or biparental inheritance (when two similarly "strong" plastids are transmitted).

Increased sesqui- and triterpene production by co-expression of HMG-CoA reductase and biotin carboxyl carrier protein in tobacco (Nicotiana benthamiana)

Terpenoids are the most diverse natural products with many industrial applications and are all synthesized from simple precursors, isopentenyl diphosphate (IPP) and its isomer dimethylallyl diphosphate (DMAPP). In plants, IPP is synthesized by two distinct metabolic pathways - cytosolic mevalonate (MVA) pathway for C15 sesquiterpene and C30 triterpene, and plastidic methylerythritol phosphate (MEP) pathway for C10 monoterpene and C20 diterpene. A number of studies have altered the metabolic gene expressions in either the MVA or MEP pathway to increase terpene production; however, it remains unknown if the alteration of the acetyl-CoA pool in plastid fatty acid biosynthesis can influence terpenoid flux. Here, we focused on the fact that acetyl-CoA is the precursor for both fatty acid biosynthesis in plastid and terpene biosynthesis in cytosol, and the metabolic impact of increased plastidic acetyl-CoA level on the cytosolic terpene biosynthesis was investigated. In tobacco leaf infiltration studies, the acetyl-CoA carboxylase complex (the enzyme supplying malonyl-CoA in plastid) was partially inhibited by overexpressing the inactive form of biotin carboxyl carrier protein (BCCP) by a negative dominant effect. Overexpression of BCCP showed 1.4-2.4-fold increase of sesquiterpenes in cytosol; however, surprisingly overexpression of BCCP linked to truncated HMG-CoA reductase (tHMGR) by a cleavable peptide 2A showed 20-40-fold increases of C15 sesquiterpenes (α-bisabolol, amorphadiene, and valerenadiene) and a 6-fold increase of C30 β-amyrin. α-Bisabolol and β-amyrin production reached 28.8 mg g-1 and 9.8 mg g-1 dry weight, respectively. Detailed analyses showed that a large increase in flux was achieved by the additive effect of BCCP- and tHMGR-overexpression, and an enhanced tHMGR activity by 2A peptide tag. Kinetic analyses showed that tHMGR-2A has a three-fold higher kcat value than tHMGR. The tHMGR-2A-BCCP1 co-expression strategy in this work provides a new insight into metabolic cross-talks and can be a generally applicable approach to over-produce sesqui- and tri-terpene in plants.

The lipid biochemistry of eukaryotic algae

Algal lipid metabolism fascinates both scientists and entrepreneurs due to the large diversity of fatty acyl structures that algae produce. Algae have therefore long been studied as sources of genes for novel fatty acids; and, due to their superior biomass productivity, algae are also considered a potential feedstock for biofuels. However, a major issue in a commercially viable "algal oil-to-biofuel" industry is the high production cost, because most algal species only produce large amounts of oils after being exposed to stress conditions. Recent studies have therefore focused on the identification of factors involved in TAG metabolism, on the subcellular organization of lipid pathways, and on interactions between organelles. This has been accompanied by the development of genetic/genomic and synthetic biological tools not only for the reference green alga Chlamydomonas reinhardtii but also for Nannochloropsis spp. and Phaeodactylum tricornutum. Advances in our understanding of enzymes and regulatory proteins of acyl lipid biosynthesis and turnover are described herein with a focus on carbon and energetic aspects. We also summarize how changes in environmental factors can impact lipid metabolism and describe present and potential industrial uses of algal lipids.

Small RNA sequencing reveals dynamic microRNA expression of important nutrient metabolism during development of Camellia oleifera fruit

To obtain insight into the function of miRNAs in the synthesis and storage of important nutrients during the development of Camellia oleifera fruit, Illumina sequencing of flower and fruit small-RNA was conducted. The results revealed that 797 miRNAs were significantly differentially expressed between flower and fruit samples of Camellia oleifera. Through integrated GO and KEGG function annotations, it was determined that the miRNA target genes were mainly involved in metabolic pathways, plant hormone signal transduction, fruit development, mitosis and regulation of biosynthetic processes. Carbohydrate accumulation genes were differentially regulated by miR156, miR390 and miR395 in the fruit growth and development process. MiR477 is the key miRNA functioning in regulation of genes and involved in fatty acid synthesis. Additionally, miR156 also has the function of regulating glycolysis and nutrient transformation genes.

Legume Cytosolic and Plastid Acetyl-Coenzyme-A Carboxylase Genes Differ by Evolutionary Patterns and Selection Pressure Schemes Acting before and after Whole-Genome Duplications

Acetyl-coenzyme A carboxylase (ACCase, E.C.6.4.1.2) catalyzes acetyl-coenzyme A carboxylation to malonyl coenzyme A. Plants possess two distinct ACCases differing by cellular compartment and function. Plastid ACCase contributes to de novo fatty acid synthesis, whereas cytosolic enzyme to the synthesis of very long chain fatty acids, phytoalexins, flavonoids, and anthocyanins. The narrow leafed lupin (Lupinus angustifolius L.) represents legumes, a plant family which evolved by whole-genome duplications (WGDs). The study aimed on the contribution of these WGDs to the multiplication of ACCase genes and their further evolutionary patterns. The molecular approach involved bacterial artificial chromosome (BAC) library screening, fluorescent in situ hybridization, linkage mapping, and BAC sequencing. In silico analysis encompassed sequence annotation, comparative mapping, selection pressure calculation, phylogenetic inference, and gene expression profiling. Among sequenced legumes, the highest number of ACCase genes was identified in lupin and soybean. The most abundant plastid ACCase subunit genes were accB. ACCase genes in legumes evolved by WGDs, evidenced by shared synteny and Bayesian phylogenetic inference. Transcriptional activity of almost all copies was confirmed. Gene duplicates were conserved by strong purifying selection, however, positive selection occurred in Arachis (accB2) and Lupinus (accC) lineages, putatively predating the WGD event(s). Early duplicated accA and accB genes underwent transcriptional sub-functionalization.

A role of GUNs-Involved retrograde signaling in regulating Acetyl-CoA carboxylase 2 in Arabidopsis

In Arabidopsis thaliana (Arabidopsis), Acetyl-CoA Carboxylase 2 (ACC2) is a nuclear DNA-encoded and plastid-targeted enzyme that catalyzes the conversion of acetyl-CoA to malonyl-CoA. ACC2 improves plant growth and development when chloroplast translation is impaired. However, little is known about the upstream signals that regulate ACC2. Here, through analyzing the transcriptome changes in brz-insensitive-pale green (bpg) 2-2, a pale-green mutant with impaired chloroplast gene expression resulting from loss of the BPG2 function, we found that the level of ACC2 was significantly up-regulated. Through performing genetic analysis, we further demonstrated that loss of the GENOMES UNCOUPLED 1 (GUN1) or GUN5 function partly perturbed the up-regulation of ACC2 in the bpg2-2 mutant, whereas ABA INSENSITIVE 4 (ABI4)-function-loss had no clear effect on the ACC2 expression. Furthermore, when plants were treated with plastid translation inhibitors, such as lincomycin and spectinomycin, the ACC2 transcriptional level was also markedly increased in a GUN-dependent manner. In conclusion, our results suggested that the GUN-involved plastid-to-nucleus retrograde communication played a role in regulating ACC2 in Arabidopsis.

Tung Tree (Vernicia fordii, Hemsl.) Genome and Transcriptome Sequencing Reveals Co-Ordinate Up-Regulation of Fatty Acid β-Oxidation and Triacylglycerol Biosynthesis Pathways During Eleostearic Acid Accumulation in Seeds

The tung tree (Vernicia fordii) is one of only a few plant species that produces high oil-yielding seeds rich in α-eleostearic acid (α-ESA, 18:3Δ9cis, 11trans, 13trans), a conjugated trienoic fatty acid with valuable industrial and medical properties. Previous attempts have been made to engineer tung oil biosynthesis in transgenic oilseed crops, but these efforts have met with limited success. Here we present a high-quality genome assembly and developing seed transcriptomic data set for this species. Whole-genome shotgun sequencing generated 176 Gb of genome sequence data used to create a final assembled sequence 1,176,320 kb in size, with a scaffold N50 size of >474 kb, and containing approximately 47,000 protein-coding genes. Genomic and transcriptomic data revealed full-length candidate genes for most of the known and suspected reactions that are necessary for fatty acid desaturation/conjugation, acyl editing and triacylglycerol biosynthesis. Seed transcriptomic analyses also revealed features unique to tung tree, including unusual transcriptional profiles of fatty acid biosynthetic genes, and co-ordinated (and seemingly paradoxical) simultaneous up-regulation of both fatty acid β-oxidation and triacylglycerol biosynthesis in mid-development seeds. The precise temporal control of the expression patterns for these two pathways may account for α-ESA enrichment in tung seeds, while controlling the levels of potentially toxic by-products. Deeper understanding of these processes may open doors to the design of engineered oilseeds containing high levels of α-ESA.

Seeds as oil factories

Studying seed oil metabolism. The seeds of higher plants represent valuable factories capable of converting photosynthetically derived sugars into a variety of storage compounds, including oils. Oils are the most energy-dense plant reserves and fatty acids composing these oils represent an excellent nutritional source. They supply humans with much of the calories and essential fatty acids required in their diet. These oils are then increasingly being utilized as renewable alternatives to petroleum for the chemical industry and for biofuels. Plant oils therefore represent a highly valuable agricultural commodity, the demand for which is increasing rapidly. Knowledge regarding seed oil production is extensively exploited in the frame of breeding programs and approaches of metabolic engineering for oilseed crop improvement. Complementary aspects of this research include (1) the study of carbon metabolism responsible for the conversion of photosynthetically derived sugars into precursors for fatty acid biosynthesis, (2) the identification and characterization of the enzymatic actors allowing the production of the wide set of fatty acid structures found in seed oils, and (3) the investigation of the complex biosynthetic pathways leading to the production of storage lipids (waxes, triacylglycerols). In this review, we outline the most recent developments in our understanding of the underlying biochemical and molecular mechanisms of seed oil production, focusing on fatty acids and oils that can have a significant impact on the emerging bioeconomy.

Improvement of Spinosad Production upon Utilization of Oils and Manipulation of β-Oxidation in a High-Producing Saccharopolyspora spinosa Strain

Spinosad, a member of polyketide-derived macrolides produced in the actinomycete Saccharopolyspora spinosa, has been developed as a broad-spectrum and effective insecticide. The β-oxidation pathway could be an important source of building blocks for the biosynthesis of spinosad, thus the effect of vegetable oils on the production of spinosad in a high-yield strain was investigated. The spinosad production increased significantly with the addition of strawberry seed oil (511.64 mg/L) and camellia oil (520.07 mg/L) compared to the control group without oil (285.76 mg/L) and soybean oil group (398.11 mg/L). It also revealed that the addition of oils would affect the expression of genes involved in fatty acid metabolism, precursor supply, and oxidative stress. The genetically engineered strain, in which fadD1 and fadE genes of Streptomyces coelicolor were inserted, produced spinosad up to 784.72 mg/L in the medium containing camellia oil, while a higher spinosad production level (843.40 mg/L) was detected with the addition of 0.01 mM of thiourea.

Effects of Medium- and Long-Chain Triacylglycerols on Lipid Metabolism and Gut Microbiota Composition in C57BL/6J Mice

Obesity is related to an increasing risk of chronic diseases. Medium- and long-chain triacylglycerols (MLCT) have been recognized as a promising choice to reduce body weight. In this study, three MLCT with different contents of medium-chain fatty acids (MCFA) (10-30%, w/w) were prepared, and their effects on lipid metabolism and fecal gut microbiota composition of C57BL/6J mice were systematically investigated. MLCT with 30% (w/w) MCFA showed the best performance in decreasing body weight gain as well as optimizing serum lipid parameters and liver triacylglycerol content. The expression levels of genes encoding enzymes for fatty acid degradation increased markedly and expression levels of genes encoding enzymes for de novo fatty acid biosynthesis decreased significantly in the liver of mice treated with MLCT containing 30% (w/w) MCFA. Interestingly, the dietary intake of a high fat diet containing MLCT did significantly decrease the ratio of Firmicutes to Bacteroidetes and down-regulate the relative abundance of Proteobacteria that may attribute to weight loss. Furthermore, we found a notable increase in the total short-chain fatty acid (SCFA) content in feces of mice on a MLCT containing diet. All these results may be concomitantly responsible for the antiobesity effect of MLCT with relatively high contents of MCFA.

High throughput sequencing of small RNAs reveals dynamic microRNAs expression of lipid metabolism during Camellia oleifera and C. meiocarpa seed natural drying

BACKGROUND

Camellia species are ancient oilseed plants with a history of cultivation over two thousand years. Prior to oil extraction, natural seed drying is often practiced, a process affecting fatty acid quality and quantity. MicroRNAs (miRNA) of lipid metabolism associated with camellia seed natural drying are unexplored. To obtain insight into the function of miRNAs in lipid metabolism during natural drying, Illumina sequencing of C. oleifera and C. meiocarpa small-RNA was conducted.

RESULTS

A total of 274 candidate miRNAs were identified and 3733 target unigenes were annotated by performing a BLASTX. Through integrated GO and KEGG function annotation, 23 miRNA regulating 131 target genes were identified as lipid metabolism, regulating fatty acid biosynthesis, accumulation and catabolism. We observed one, two, and four miRNAs of lipid metabolism which were specially expressed in C. Meiocarpa, C. oleifera, and the two species collectively, respectively. At 30% moisture contents, C. meiocarpa and C. oleifer produced nine and eight significant differentially expressed miRNAs, respectively, with high fatty acid synthesis and accumulation activities. Across the two species, 12 significant differentially expressed miRNAs were identified at the 50% moisture content.

CONCLUSIONS

Sequencing of small-RNA revealed the presence of 23 miRNAs regulating lipid metabolism in camellia seed during natural drying and permitted comparative miRNA profiles between C. Meiocarpa and C. oleifera. Furthermore, this study successfully identified the best drying environment at which the quantity and quality of lipid in camellia seed are at its maximum.

Histological changes, lipid metabolism and oxidative stress in the liver of Bufo gargarizans exposed to cadmium concentrations

Chinese toad (Bufo gargarizans) were exposed to different concentrations of cadmium (5, 50, 100, 200 and 500 μg Cd L^-1) from Gosner stage 3-42. Metamorphosis rate, body weight, total length and body length were measured. Histological alterations in thyroid gland and liver were examined. Changes in hepatocyte were also examined using Transmission electron microscopic. In addition, the mRNA expression of several genes involved in lipid metabolism, oxidative stress and thyroid hormones signaling pathways were also measured. Our results showed that 200 and 500 μg Cd L^-1 decreased the metamorphosis rate and inhibited the body size of B. gargarizans larvae at G42. Moreover, histological examinations have clearly exhibited that cadmium caused liver damage. Ultrastructural examination revealed lipid accumulation and abnormal mitochondria. Exposure to 200 and 500 μg Cd L^-1 significantly up-regulated mRNA expression of D2, SOD, GPx, ACC and FAE, but down-regulated mRNA expression of TRα, TRβ, PPARα, ACOX, CPT and SCP. However, low Cd concentration (5, 50 and 100) exposure did not cause any effect in genes expression. Thus, we conclude that high Cd concentrations could affect the normal processes of lipid metabolism though increasing lipid synthesis and reducing the ability of fatty acid β-oxidation, and disturb thyroid hormone pathways in liver, and induced oxidative stress. In addition, lipid metabolism might be regulated by THs. To our knowledge, the present study is the first to report the influence of cadmium on hepatic lipid metabolism in B. gargarizans and will greatly provide new insights into cadmium hepatotoxicity in amphibian.

Analysis of Arabidopsis Accessions Hypersensitive to a Loss of Chloroplast Translation

Natural accessions of Arabidopsis (Arabidopsis thaliana) differ in their ability to tolerate a loss of chloroplast translation. These differences can be attributed in part to variation in a duplicated nuclear gene (ACC2) that targets homomeric acetyl-coenzyme A carboxylase (ACCase) to plastids. This functional redundancy allows limited fatty acid biosynthesis to occur in the absence of heteromeric ACCase, which is encoded in part by the plastid genome. In the presence of functional ACC2, tolerant alleles of several nuclear genes, not yet identified, enhance the growth of seedlings and embryos disrupted in chloroplast translation. ACC2 knockout mutants, by contrast, are hypersensitive. Here we describe an expanded search for hypersensitive accessions of Arabidopsis, evaluate whether all of these accessions are defective in ACC2, and characterize genotype-to-phenotype relationships for homomeric ACCase variants identified among 855 accessions with sequenced genomes. Null alleles with ACC2 nonsense mutations, frameshift mutations, small deletions, genomic rearrangements, and defects in RNA splicing are included among the most sensitive accessions examined. By contrast, most missense mutations affecting highly conserved residues failed to eliminate ACC2 function. Several accessions were identified where sensitivity could not be attributed to a defect in either ACC2 or Tic20-IV, the chloroplast membrane channel required for ACC2 uptake. Overall, these results underscore the central role of ACC2 in mediating Arabidopsis response to a loss of chloroplast translation, highlight future applications of this system to analyzing chloroplast protein import, and provide valuable insights into the mutational landscape of an important metabolic enzyme that is highly conserved throughout eukaryotes.

Positive Selection in Rapidly Evolving Plastid-Nuclear Enzyme Complexes

Rates of sequence evolution in plastid genomes are generally low, but numerous angiosperm lineages exhibit accelerated evolutionary rates in similar subsets of plastid genes. These genes include clpP1 and accD, which encode components of the caseinolytic protease (CLP) and acetyl-coA carboxylase (ACCase) complexes, respectively. Whether these extreme and repeated accelerations in rates of plastid genome evolution result from adaptive change in proteins (i.e., positive selection) or simply a loss of functional constraint (i.e., relaxed purifying selection) is a source of ongoing controversy. To address this, we have taken advantage of the multiple independent accelerations that have occurred within the genus Silene (Caryophyllaceae) by examining phylogenetic and population genetic variation in the nuclear genes that encode subunits of the CLP and ACCase complexes. We found that, in species with accelerated plastid genome evolution, the nuclear-encoded subunits in the CLP and ACCase complexes are also evolving rapidly, especially those involved in direct physical interactions with plastid-encoded proteins. A massive excess of nonsynonymous substitutions between species relative to levels of intraspecific polymorphism indicated a history of strong positive selection (particularly in CLP genes). Interestingly, however, some species are likely undergoing loss of the native (heteromeric) plastid ACCase and putative functional replacement by a duplicated cytosolic (homomeric) ACCase. Overall, the patterns of molecular evolution in these plastid-nuclear complexes are unusual for anciently conserved enzymes. They instead resemble cases of antagonistic coevolution between pathogens and host immune genes. We discuss a possible role of plastid-nuclear conflict as a novel cause of accelerated evolution.