白蜡虫蜡花微生物多样性分析

【目的】探究白蜡虫Ericerus pela(Chavannes)雄若虫分泌的蜡花中微生物的多样性,比较不同厚度蜡花(随雄若虫发育蜡质层厚度增加)中细菌及真菌的种类和变化。【方法】采用Mi Seq高通量测序方法对不同发育阶段白蜡虫雄若虫分泌的蜡花中细菌16S rRNA和真菌ITS进行测序,利用Mothur软件计算蜡花中细菌和真菌的操作分类单元(operational taxonomic unit,OTU)及其丰富度、Alpha多样性分析。【结果】细菌3个样品共获470个OTU,真菌2个样品共获264个OTU。细菌共鉴定出18门30纲92科173属;真菌共鉴定出3门15纲43科68属。其中丛毛单胞菌属Comamonas细菌在蜡花中为优势菌,分别占前、中、后期雄若虫分泌的蜡花中细菌总量的79.79%,41.61%和46.86%;枝胞属Cladosporium在前期雄若虫分泌的蜡花中占真菌总量的17.01%,隐球菌属Cryptococcus在后期雄若虫分泌的蜡花中占真菌总量的60.84%,是蜡花中真菌重要组成部分。【结论】不同发育阶段雄若虫分泌的蜡花中细菌及真菌群落存在差异,随着蜡花厚度增加,细菌多样性先增加后减少,而真菌多样性降低。     

白蜡虫七种寄主植物枝条树皮比较解剖研究

采用常规石蜡切片法解剖观察了白蜡虫7种寄主植物一年生枝条树皮横切面结构特征,结果表明:白蜡虫7种寄主植物一年生枝条树皮从内到外由次生韧皮部、初生韧皮部纤维束、皮层和周皮组成;次生韧皮部横向系统均由筛管、伴胞和薄壁细胞组成;轴向系统由射线组成。木栓层以美国白蜡和流苏细胞层数最多,达10～12层;华南小蜡、紫药女贞和白枪杆次之,为5～8层;女贞和白蜡树最少,分别为2～3和3～4层。初生韧皮部纤维束排列整齐连接为带状或分散,女贞属纤维连接成带状,白蜡属和流苏属纤维分散。带状纤维层厚薄不均,厚度在26.93±13～59.15±7μm之间,以白枪杆纤维层最厚,为59.15±7μm;美洲白蜡次之,为50.05±7μm;白蜡树最薄,为26.93±13μm。分散型纤维束直径在25.12±13～76.15±36μm之间,纤维束直径大小顺序为:流苏(76.15±36μm)>紫药女贞(43.44±10μm)>女贞(25.12±13μm)。女贞、紫药女贞和流苏纤维束间距分别为78.53±39μm、149.78±27μm和212.02±95μm。次生韧皮部厚度在48.52±12～377.44±24μm之间,以女贞的次生韧皮部最厚,达377.44±24μm,华南小蜡最薄,为48.52±12μm。树皮次生韧皮部厚、木栓层数少和纤维束直径小为白蜡虫优良寄主植物的显著特征。     

环境因子对白蜡虫泌蜡的影响

白蜡虫是一种具有重大的经济价值资源昆虫,白蜡虫分泌的白蜡是一种重要的天然化工原料。研究了不同温度、湿度、光照等因子对白蜡虫泌蜡的影响,试验种群和自然种群研究结果表明,白蜡虫在15～25℃下能正常分泌白蜡和生长发育,在30℃以上的持续恒温下,白蜡虫能分泌白蜡,但泌蜡量低,不能正常生长发育,化蛹,2龄末期死亡;在高湿度（年相对湿度〉80％）、低光照（〈1600h／a）条件下,白蜡虫泌蜡量高,但种群不能正常生长发育,雌虫死亡率高,不能完成生活史。多因素分析表明,白蜡虫泌蜡对温度不敏感,影响白蜡虫泌蜡的关键因子是湿度和光照,适于白蜡虫泌蜡的环境因子为：温度15～25℃、年降雨量1300～2000mm,年相对湿度〉80％,泌蜡期5～8月份的相对湿度〉90％,年光照时数〈1600h／a。根据在峨嵋、昭通、昆明等地对白蜡虫的生态适应性观察和分析,白蜡虫泌蜡高的环境不是白蜡虫适生区域,白蜡虫适生区域主要生态指标为：年均温11～16℃,降雨量800～1200mm／年,年相对湿度65％～75％,年光照时数为1900～2500h／a。     

影响白蜡虫泌蜡主要气候因子及白蜡虫生态适应性分析

白蜡虫是一种具有重要经济价值的资源昆虫,其生态适应性问题长期存在争议。本文对四川 峨嵋、云南昆明、昭通等地白蜡虫自然种群生态学和泌蜡生态特性进行了对比研究。泌蜡与 种群死亡率的研究结果证实,在不利于种群生长的环境中白蜡虫的泌蜡量较高,死亡率也高; 而在适生环境中的泌蜡量较低,死亡率较低。故认为,传统上以白蜡虫泌蜡量的高低来作为适应生态环境的判断标准是不适合的。本文还从白蜡虫泌蜡生态适应性的角度分析了“高山产虫、低山产蜡”的原因,讨论了白蜡虫的生态适应性,得出白蜡虫适生区域主要生态指标为：年均温11℃～16℃,雨量800～1 200 mm／a,年相对湿度75％左右,年光照时数为1 900～2 500 h／a。提出白蜡虫泌蜡是其为适应环境的一种自身的保护性反应和生态对策,是对不良环境的一种抵御性反应。     

Synergistic roles of acyl‐CoA binding protein (ACBP1) and sterol carrier protein 2 (SCP2) in Toxoplasma lipid metabolism

Toxoplasma gondii relies on apicoplast‐localised FASII pathway and endoplasmic reticulum‐associated fatty acid elongation pathway for the synthesis of fatty acids, which flow through lipid metabolism mainly in the form of long‐chain acyl‐CoA (LCACoAs) esters. Functions of Toxoplasma acyl‐CoA transporters in lipid metabolism remain unclear. Here, we investigated the roles of acyl‐CoA‐binding protein (TgACBP1) and a sterol carrier protein‐2 (TgSCP2) as cytosolic acyl‐CoA transporters in lipid metabolism. The fluormetric binding assay and yeast complementation confirmed the acyl‐CoA binding activities of TgACBP1 and TgSCP2, respectively. Disruption of either TgACBP1 or TgSCP2 caused no obviously phenotypic changes, whereas double disruption resulted in defects in intracellular growth and virulence to mice. Gas chromatography coupled with mass spectrometry (GC–MS) results showed that TgACBP1 or TgSCP2 disruption alone led to decreased abundance of C18:1, whereas double disruption resulted in reduced abundance of C18:1, C22:1, and C24:1. ¹³C labelling assay combined with GC–MS showed that double disruption of TgACBP1 and TgSCP2 led to reduced synthesis rates of C18:0, C22:1, and C24:1. Furthermore, high performance liquid chromatography coupled with high resolution mass spectrometry (HPLC‐HRMS) was used for lipidomic analysis of parasites and indicated that loss of TgACBP1 and TgSCP2 caused serious defects in production of glycerides and phospholipids. Collectively, TgACBP1 and TgSCP2 play synergistic roles in lipid metabolism in T. gondii.     

Arabidopsis ketoacyl‐CoA synthase 16 (KCS16) forms C36/C38 acyl precursors for leaf trichome and pavement surface wax

The aliphatic waxes sealing plant surfaces against environmental stress are generated by fatty acid elongase complexes, each containing a β‐ketoacyl‐CoA synthase (KCS) enzyme that catalyses a crucial condensation forming a new C─C bond to extend the carbon backbone. The relatively high abundance of C₃₅ and C₃₇ alkanes derived from C₃₆ and C₃₈ acyl‐CoAs in Arabidopsis leaf trichomes (relative to other epidermis cells) suggests differences in the elongation machineries of different epidermis cell types, possibly involving KCS16, a condensing enzyme expressed preferentially in trichomes. Here, KCS16 was found expressed primarily in Arabidopsis rosette leaves, flowers and siliques, and the corresponding protein was localized to the endoplasmic reticulum. The cuticular waxes on young leaves and isolated leaf trichomes of ksc16 loss‐of‐function mutants were depleted of C₃₅ and C₃₇ alkanes and alkenes, whereas expression of Arabidopsis KCS16 in yeast and ectopic overexpression in Arabidopsis resulted in accumulation of C₃₆ and C₃₈ fatty acid products. Taken together, our results show that KCS16 is the sole enzyme catalysing the elongation of C₃₄ to C₃₈ acyl‐CoAs in Arabidopsis leaf trichomes and that it contributes to the formation of extra‐long compounds in adjacent pavement cells.     

Differential expression patterns of two delta‐9‐acyl‐CoA desaturases in Thitarodes pui (Lepidoptera: Hepialidae) during different seasons and cold exposure

Thitarodes pui larvae have a limited distribution in the Tibetan Plateau and are the host of a parasitic fungus, Ophiocordyceps sinensis. Low temperature is a main environmental stress. However, understanding of T. pui cold adaptation mechanisms is insufficient. Delta‐9‐acyl‐CoA desaturase (D9D) is closely correlated with cold adaptation for many organisms. To further understand the cold adaptation processes in T. pui larvae, two D9Ds, TpdesatA and TpdesatB were sequenced, and expression patterns were investigated during different seasons and cold exposure (under 0°C) in the laboratory. The full lengths of two cDNAs are 1,290 bp and 1,603 bp, and the ORFs encode a polypeptide of 348 and 359 amino acids, respectively. Four transmembrane domains, three conserved histidine residues and five hydrophobic regions exist in these two sequences. The expression level of TpdesatA is up‐regulated in the long‐term cold exposure and negatively correlated with temperature in seasonal patterns. TpdesatB responds to cold temperature in short‐term cold exposure and positively corresponds temporarily in seasonal expression. Two D9Ds may have different substrate specificities, TpdesatA tends to use C16:0 and C18:0 as substrate while TpdesatB prefers C18:0. In conclusion, TpdesatA may play a very important role in T. pui cold tolerance and TpdesatB regulates function in short‐term cold exposure and content change of fatty acids in the body.     

Associations of polymorphisms in the promoter I of bovine acetyl‐CoA carboxylase‐α gene with beef fatty acid composition

The objectives of this study were to identify single nucleotide polymorphisms (SNPs) in the promoter I (PI) region of the bovine acetyl‐CoA carboxylase‐α (ACACA) gene and to evaluate the extent to which they were associated with lipid‐related traits. Eight novel SNPs were identified, which were AJ276223:g.2064T>A (SNP1), g.2155C>T (SNP2), g.2203G>T (SNP3), g.2268T>C (SNP4), g.2274G>A (SNP5), g.2340A>G (SNP6), g.2350T>C (SNP7) and g.2370A>G (SNP8). Complete linkage disequilibrium was observed among SNP1, 2, 4, 5, 6 and 8. Phenotypic data were collected from 573 cross‐bred steers with six sire breeds, including Hereford, Angus, Brangus, Beefmaster, Bonsmara and Romosinuano. The genotypes of SNP1/2/4/5/6/8 were significantly associated with adjusted backfat thickness. The genotypes of SNP3 were significantly associated with triacylglycerol (TAG) content and fatty acid composition of longissimus dorsi muscle (LM) in Brangus‐, Romosinuano‐ and Bonsmara‐sired cattle. Cattle with g.2203GG genotype had greater concentrations of TAG, total lipid, total saturated fatty acid and total monounsaturated fatty acid than did cattle with g.2203GT genotype. The genotypes of SNP7 were significantly associated with fatty acid composition of LM. Cattle with genotype g.2350TC had greater amounts of several fatty acids in LM than did cattle with genotype g.2350CC. Our results suggested that the SNPs in the PI region of ACACA gene are associated with variations in the fatty acid contents in LM.     

Chlamydomonas carries out fatty acid β‐oxidation in ancestral peroxisomes using a bona fide acyl‐CoA oxidase

Peroxisomes are thought to have played a key role in the evolution of metabolic networks of photosynthetic organisms by connecting oxidative and biosynthetic routes operating in different compartments. While the various oxidative pathways operating in the peroxisomes of higher plants are fairly well characterized, the reactions present in the primitive peroxisomes (microbodies) of algae are poorly understood. Screening of a Chlamydomonas insertional mutant library identified a strain strongly impaired in oil remobilization and defective in Cre05.g232002 (CrACX2), a gene encoding a member of the acyl‐CoA oxidase/dehydrogenase superfamily. The purified recombinant CrACX2 expressed in Escherichia coli catalyzed the oxidation of fatty acyl‐CoAs into trans‐2‐enoyl‐CoA and produced H₂O₂. This result demonstrated that CrACX2 is a genuine acyl‐CoA oxidase, which is responsible for the first step of the peroxisomal fatty acid (FA) β‐oxidation spiral. A fluorescent protein‐tagging study pointed to a peroxisomal location of CrACX2. The importance of peroxisomal FA β‐oxidation in algal physiology was shown by the impact of the mutation on FA turnover during day/night cycles. Moreover, under nitrogen depletion the mutant accumulated 20% more oil than the wild type, illustrating the potential of β‐oxidation mutants for algal biotechnology. This study provides experimental evidence that a plant‐type FA β‐oxidation involving H₂O₂‐producing acyl‐CoA oxidation activity has already evolved in the microbodies of the unicellular green alga Chlamydomonas reinhardtii.     

Pex20p functions as the receptor for non‐PTS1/non‐PTS2 acyl‐CoA oxidase import into peroxisomes of the yeast Yarrowia lipolytica

Most soluble proteins targeted to the peroxisomal matrix contain a C‐terminal peroxisome targeting signal type 1 (PTS1) or an N‐terminal PTS2 that is recognized by the receptors Pex5p and Pex7p, respectively. These receptors cycle between the cytosol and peroxisome and back again for multiple rounds of cargo delivery to the peroxisome. A small number of peroxisomal matrix proteins, including all six isozymes of peroxisomal fatty acyl‐CoA oxidase (Aox) of the yeast Yarrowia lipolytica, contain neither a PTS1 nor a PTS2. Pex20p has been shown to function as a co‐receptor for Pex7p in the import of PTS2 cargo into peroxisomes. Here we show that cells of Y. lipolytica deleted for the PEX20 gene fail to import not only the PTS2‐containing protein 3‐ketoacyl‐CoA thiolase (Pot1p) but also the non‐PTS1/non‐PTS2 Aox isozymes. Pex20p binds directly to Aox isozymes Aox3p and Aox5p, which requires the C‐terminal Wxxx(F/Y) motif of Pex20p. A W411G mutation in the C‐terminal Wxxx(F/Y) motif causes Aox isozymes to be mislocalized to the cytosol. Pex20p interacts physically with members of the peroxisomal import docking complex, Pex13p and Pex14p. Our results are consistent with a role for Pex20p as the receptor for import of the non‐PTS1/non‐PTS2 Aox isozymes into peroxisomes.     

Characterization of cis-elements required for vascular expression of the cinnamoyl CoA reductase gene and for protein-DNA complex formation

Cinnamoyl-CoA reductase (CCR) catalyses the first specific step in the biosynthesis of monolignols, the monomeric units of lignins. We examined the developmental regulation of the Eucalyptus gunnii EgCCR promoter by analysing the expression of EgCCR-GUS fusions in tobacco. EgCCR promoter activity was strongest in lignified organs (stems and roots) consistent with the EgCCR mRNA level in these organs. Histochemical analysis showed expression in vascular tissues (cambium, young differentiating xylem, ray cells, internal and external phloem) of stems and roots in agreement with in situ hybridization data. Promoter deletion analysis and gain-of-function experiments identified the sequences between positions -119 and -77 as necessary and sufficient for expression in vascular tissues of stems. Electrophoretic mobility-shift assays showed that this region is specifically recognized by nuclear proteins present in tobacco stems, giving rise to two retarded complexes, LMC1 and LMC2. Using overlapping EgCCR fragments and mutated oligonucleotides as competitors in gel-shift assays, two DNA-protein interaction sites were mapped. Finally, the role of protein-protein interactions in the formation of the LMC1 and LMC2 complexes was investigated using the detergent sodium deoxycholate, and protein fractionation onto a heparin Sepharose column.     

Evidence for the involvement of polyunsaturated fatty acids in the regulation of long-chain acyl CoA thioesterases and peroxisome proliferation in rat carcinosarcoma

The feeding of high-fat diets rich in polyunsaturated fatty acids (PUFAs) caused a marked increase in the acyl CoA thioesterase activity of the Walker 256 tumour. Diets containing lower levels of PUFAs did not alter the activity of acyl CoA thioesterase and the exposure of LLC-WRC256 tumour cells, in culture, to PUFAs (150 microM) also was ineffective in altering activity. The tumours from n-3 PUFA-rich and control diets were analysed by transmission electron microscopy in order to compare peroxisomal content. The presence of PUFAs led to an almost 10-fold increase in the number of peroxisomes present in the tumour tissue. A common feature of the PUFA-treated tumour was the presence of many cells containing highly condensed heterochromatin at the periphery of the nucleus, indicative of apoptosis. The sparsity of endoplasmic reticulum and the lack of detection of mitochondrial acyl CoA thioesterase, MTE-I, led to the conclusion that the increase in tumour acyl CoA thioesterase activity may be due to an increase in the activity of the peroxisomal enzyme.     

A novel role for central ACBP/DBI as a regulator of long‐chain fatty acid metabolism in astrocytes

Acyl‐CoA‐binding protein (ACBP) is a ubiquitously expressed protein that binds intracellular acyl‐CoA esters. Several studies have suggested that ACBP acts as an acyl‐CoA pool former and regulates long‐chain fatty acids (LCFA) metabolism in peripheral tissues. In the brain, ACBP is known as Diazepam‐Binding Inhibitor, a secreted peptide acting as an allosteric modulator of the GABA_A receptor. However, its role in central LCFA metabolism remains unknown. In the present study, we investigated ACBP cellular expression, ACBP regulation of LCFA intracellular metabolism, FA profile, and FA metabolism‐related gene expression using ACBP‐deficient and control mice. ACBP was mainly found in astrocytes with high expression levels in the mediobasal hypothalamus. We demonstrate that ACBP deficiency alters the central LCFA‐CoA profile and impairs unsaturated (oleate, linolenate) but not saturated (palmitate, stearate) LCFA metabolic fluxes in hypothalamic slices and astrocyte cultures. In addition, lack of ACBP differently affects the expression of genes involved in FA metabolism in cortical versus hypothalamic astrocytes. Finally, ACBP deficiency increases FA content and impairs their release in response to palmitate in hypothalamic astrocytes. Collectively, these findings reveal for the first time that central ACBP acts as a regulator of LCFA intracellular metabolism in astrocytes.

     

Investigating the role of native propionyl‐CoA and methylmalonyl‐CoA metabolism on heterologous polyketide production in Escherichia coli

6‐Deoxyerythronolide B (6dEB) is the macrocyclic aglycone precursor of the antibiotic natural product erythromycin. Heterologous production of 6dEB in Escherichia coli was accomplished, in part, by designed over‐expression of a native prpE gene (encoding a propionyl‐CoA synthetase) and heterologous pcc genes (encoding a propionyl‐CoA carboxylase) to supply the needed propionyl‐CoA and (2S)‐methylmalonyl‐CoA biosynthetic substrates. Separate E. coli metabolism includes three enzymes, Sbm (a methylmalonyl‐CoA mutase), YgfG (a methylmalonyl‐CoA decarboxylase), and YgfH (a propionyl‐CoA:succinate CoA transferase), also involved in propionyl‐CoA and methylmalonyl‐CoA metabolism. In this study, the sbm, ygfG, and ygfH genes were individually deleted and over‐expressed to investigate their effect on heterologous 6dEB production. Our results indicate that the deletion and over‐expression of sbm did not influence 6dEB production; ygfG over‐expression reduced 6dEB production by fourfold while ygfH deletion increased 6dEB titers from 65 to 129 mg/L in shake flask experiments. It was also found that native E. coli metabolism could support 6dEB biosynthesis in the absence of exogenous propionate and the substrate provision pcc genes. Lastly, the effect of the ygfH deletion was tested in batch bioreactor cultures in which 6dEB titers improved from 206 to 527 mg/L. Biotechnol. Bioeng. 2010; 105: 567–573. © 2009 Wiley Periodicals, Inc.     

Characterization of triacsin C inhibition of short-, medium-, and long-chain fatty acid: CoA ligases of human liver

Short-, medium-, and long-chain fatty acid:CoA ligases from human liver were tested for their sensitivity to inhibition by triacsin C. The short-chain fatty acid:CoA ligase was inhibited less than 10% by concentrations of triacsin C as high as 80 microM. The two mitochondrial xenobiotic/medium-chain fatty acid:CoA ligases (XM-ligases), HXM-A and HXM-B, were partially inhibited by triacsin C, and the inhibitions were characterized by low affinity for triacsin C (K(I) values > 100 microM). These inhibitions were found to be the result of triacsin C competing with medium-chain fatty acid for binding at the active site. The microsomal and mitochondrial forms of long-chain fatty acid:CoA ligase (also termed long-chain fatty acyl-CoA synthetase, or long-chain acyl-CoA synthetase LACS) were potently inhibited by triacsin C, and the inhibition had identical characteristics for both LACS forms. Dixon plots of this inhibition were biphasic. There is a high-affinity site with a K(I) of 0.1 microM that accounts for a maximum of 70% of the inhibition. There is also a low affinity site with a K(I) of 6 microM that accounts for a maximum of 30% inhibition. Kinetic analysis revealed that the high-affinity inhibition of the mitochondrial and microsomal LACS forms is the result of triacsin C binding at the palmitate substrate site.The high-affinity triacsin C inhibition of both the mitochondrial and microsomal LACS forms was found to require a high concentration of free Mg(2+), with the EC(50) for inhibition being 3 mM free Mg(2+). The low affinity triacsin C inhibition was also enhanced by Mg(2+). The data suggests that Mg(2+) promotes triacsin C inhibition of LACS by enhancing binding at the palmitate binding site. In contrast, the partial inhibition of the XM-ligases by triacsin C, which showed only a low-affinity component, did not require Mg(2+).     

Modification of phospholipids fatty acid composition in reuber H35 hepatoma cells: effect on HMG-CoA reductase activity

There is controversy about the effect of saturated and polyunsaturated fats on 3-hydroxy-3-methylglutaryl-CoA (HMG-CoA) reductase, the main regulatory enzyme of cholesterogenic pathway. Results from dietary studies are difficult to interpret because diets normally contain a mixture of fatty acids. Therefore, we have used Reuber H35 hepatoma cells whose phospholipids were enriched in different individual fatty acids and have studied their effects on the cellular reductase activity. Lauric, myristic, eicosapentaenoic (EPA), and docosahexaenoic (DHA) acids were supplemented to the culture medium coupled to bovine serum albumin. The four fatty acids were incorporated into phospholipids from cells grown in media containing whole serum or lipoprotein-poor serum (LPPS). Reductase activity of cells cultivated in a medium with LPPS was three to four times higher than those cultivated in medium with whole serum. Saturated fatty acids increased reductase activity of cells grown in medium with whole serum, whereas n-3 polyunsaturated fatty acids (PUFA) decreased it. However, both saturated and polyunsaturated fatty acids increased reductase activity when serum lipoproteins were removed. In conclusion, this is one of the first reports demonstrating that saturated and n-3 PUFA only show differential effects on HMG-CoA reductase activity in the presence of lipoproteins.     

Proliferation of mitochondria and gene expression of carnitine palmitoyltransferase and fatty acyl-CoA oxidase in rat skeletal muscle, heart and liver by hypolipidemic fatty acids

Morphological and biochemical effects were induced at the subcellular level in the skeletal muscle, heart and liver of male rats as a result of feeding with EPA, DHA, and 3-thia fatty acids. The 3-thia fatty acid, tetradecylthioacetic acid (TTA) and EPA induced mitochondrial growth in type I muscle fibers in both the diaphragm and soleus muscle, and the size distribution of mitochondrial areas followed a similar pattern. Only the 3-thia fatty acid induced mitochondrial growth in type II muscle fibers. The mean area occupied by the mitochondria and the size distribution of mitochondrial areas in both fiber types were highly similar in DHA-treated and control animals. Only the 3-thia fatty acid increased the gene-expression of carnitine palmitoyltransferase (CPT)-II in the diaphragm. In the heart, however, the gene expression decreased. In hepatocytes an increase in the mean size of mitochondria was observed after EPA treatment, concomitant with an increase in mitochondrial CPT-II gene expression. Administration of 2-methyl-substituted EPA (methyl-EPA) induced a higher rate of growth of mitochondria than EPA. At the peroxisomal level in the hepatocytes a 3-thia fatty acid, EPA, and DHA increased the areal fraction concomitant with the induction of gene expression of peroxisomal fatty acyl-CoA oxidase (FAO). In the diaphragm, mRNA levels of FAO were not affected by EPA or DHA treatment, whereas gene expression was significantly increased after 3-thia fatty acid treatment. In the heart, both 3-thia fatty acid, EPA and DHA tended to decrease the levels of FAO mRNA. The areal fraction of fat droplets in all three tissue types was significantly lower in the groups treated with 3-thia fatty acid. In the group treated with EPA a lower areal fraction of fat droplets was observed, while the DHA group was similar to the control. This indicates that EPA and DHA have different effects on mitochondrial biogenesis.     

Arabidopsis acyl‐CoA‐binding protein ACBP1 participates in the regulation of seed germination and seedling development

A family of six genes encoding acyl‐CoA‐binding proteins (ACBPs), ACBP1–ACBP6, has been characterized in Arabidopsis thaliana. In this study, we demonstrate that ACBP1 promotes abscisic acid (ABA) signaling during germination and seedling development. ACBP1 was induced by ABA, and transgenic Arabidopsis ACBP1‐over‐expressors showed increased sensitivity to ABA during germination and seedling development, whereas the acbp1 mutant showed decreased ABA sensitivity during these processes. Subsequent RNA assays showed that ACBP1 over‐production in 12‐day‐old seedlings up‐regulated the expression of PHOSPHOLIPASE Dα1 (PLDα1) and three ABA/stress‐responsive genes: ABA‐RESPONSIVE ELEMENT BINDING PROTEIN1 (AREB1), RESPONSE TO DESICCATION29A (RD29A) and bHLH‐TRANSCRIPTION FACTOR MYC2 (MYC2). The expression of AREB1 and PLDα1 was suppressed in the acbp1 mutant in comparison with the wild type following ABA treatment. PLDα1 has been reported to promote ABA signal transduction by producing phosphatidic acid, an important lipid messenger in ABA signaling. Using lipid profiling, seeds and 12‐day‐old seedlings of ACBP1‐over‐expressing lines were shown to accumulate more phosphatidic acid after ABA treatment, in contrast to lower phosphatidic acid in the acbp1 mutant. Bimolecular fluorescence complementation assays indicated that ACBP1 interacts with PLDα1 at the plasma membrane. Their interaction was further confirmed by yeast two‐hybrid analysis. As recombinant ACBP1 binds phosphatidic acid and phosphatidylcholine, ACBP1 probably promotes PLDα1 action. Taken together, these results suggest that ACBP1 participates in ABA‐mediated seed germination and seedling development.