Plastid-localised seed acyl-carrier protein of Brassica napus is encoded by a distinct, nuclear multigene family

Involvement of Arabidopsis Acyl Carrier Protein 1 in PAMP-Triggered Immunity

Plant fatty acids (FAs) and lipids are essential in storing energy and act as structural components for cell membranes and signaling molecules for plant growth and stress responses. Acyl carrier proteins (ACPs) are small acidic proteins that covalently bind the fatty acyl intermediates during the elongation of FAs. The Arabidopsis thaliana ACP family has eight members. Through reverse genetic, molecular, and biochemical approaches, we have discovered that ACP1 localizes to the chloroplast and limits the magnitude of pattern-triggered immunity (PTI) against the bacterial pathogen Pseudomonas syringae pv. tomato. Mutant acp1 plants have reduced levels of linolenic acid (18:3), which is the primary precursor for biosynthesis of the phytohormone jasmonic acid (JA), and a corresponding decrease in the abundance of JA. Consistent with the known antagonistic relationship between JA and salicylic acid (SA), acp1 mutant plants also accumulate a higher level of SA and display corresponding shifts in JA- and SA-regulated transcriptional outputs. Moreover, methyl JA and linolenic acid treatments cause an apparently enhanced decrease of resistance against P. syringae pv. tomato in acp1 mutants than that in WT plants. The ability of ACP1 to prevent this hormone imbalance likely underlies its negative impact on PTI in plant defense. Thus, ACP1 links FA metabolism to stress hormone homeostasis to be negatively involved in PTI in Arabidopsis plant defense. [Formula: see text] Copyright © 2022 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

New insights on the function of plant acyl carrier proteins from comparative and evolutionary analysis

Acyl carrier proteins (ACPs) play a central role in both plastidial and mitochondrial Type II fatty acid synthesis in plant cells. However, a large proportion of plant ACPs remain functionally uncharacterized, and their evolutionary history remains elusive. In present study, 97 putative ACPs were identified from ten angiosperm species examined. Based on phylogenetic analysis, ACP genes were grouped into plastidial (cpACP: ACP1/2/3/4/5) and mitochondrial (mtACP: mtACP1/mtACP2/mtACP3) ACPs. Protein sequence (motifs and length), tertiary structure, and gene structure (exon number, average intron length, and intron phase) were highly conserved in different ACP subclades. The differentiation of ACPs into distinct types occurred 85-98 and 45-57 million years ago. A limited proportion of ACP genes experience tandem or segmental duplication, corresponding to two rounds of whole genome duplication. Ka/Ks ratios revealed that duplicated ACP genes underwent a purifying selection. Regarding expression patterns, most ACPs were expressed constitutively and tissue-specifically. Notably, the average expression levels of ACP1, mtACP3, and mtACP1 were positively correlated with those of ACP3, ACP4, and mtACP2, respectively. Analysis of cis-elements showed that seven motifs (CACTFTPPCA1, DOFCOREZM, GT1CONSENSUS, CAATBOX1, ARR1AT, POLLEN1LELAT52, and GATABOX) related to tissue-specific, ABA, and light-mediated gene regulation were ubiquitous in all ACPs investigated, which shed new light on the regulation patterns of these central enzymatic partners of the FAS system. This study presents a thorough overview of angiosperm ACP gene families and provides informative clues for the functional characterization of plant ACPs in the future.

A label-free differential proteomics analysis reveals the effect of melatonin on promoting fruit ripening and anthocyanin accumulation upon postharvest in tomato

To better understand the function of melatonin in tomato fruit ripening and quality improvement, a label-free quantitation method was used to investigate the proteins that differ between the control (CK) and 50 μm melatonin treatment (M50) fruits. Proteomics data identified 241 proteins that were significantly influenced by melatonin. These proteins were involved in several ripening-related pathways, including cell wall metabolism, oxidative phosphorylation, carbohydrate, and fatty acid metabolism. Moreover, the application of exogenous melatonin increased eight proteins that are related to anthocyanin accumulation during fruit ripening. Additionally, the affected protein levels correlated with the corresponding gene transcript levels. Further, the total anthocyanin content from M50 increased by 52%, 48%, and 50% at 5, 8, and 13 DAT (day after melatonin treatment), respectively. The melatonin-mediated promotion of fruit ripening and quality might be due to the altered proteins involved in processes associated with ripening. In this work, we indicated that a senescence-related protein was downregulated in the M50 fruit, while a cell apoptosis inhibitor (API5) protein was upregulated. In addition, peroxidases (POD9, POD12, peroxidase p7-like) and catalase (CAT3) significantly increased in the M50 fruits. Based on the previous studies and our data, we inferred that melatonin might be positively related to fruit ripening but negatively related to fruit senescence. This research provides insights into the physiological and molecular mechanisms underlying melatonin-mediated fruit ripening as well as the anthocyanin formation process in tomato fruit at the protein concentration level, and we reveal possible candidates for regulation of anthocyanin formation during fruit ripening.

A soybean acyl carrier protein, GmACP, is important for root nodule symbiosis

Legumes (members of family Fabaceae) establish a symbiotic relationship with nitrogen-fixing soil bacteria (rhizobia) to overcome nitrogen source limitation. Single root hair epidermal cells serve as the entry point for bacteria to infect the host root, leading to development of a new organ, the nodule, which the bacteria colonize. In the present study, the putative role of a soybean acyl carrier protein (ACP), GmACP (Glyma18g47950), was examined in nodulation. ACP represent an essential cofactor protein in fatty acid biosynthesis. Phylogenetic analysis of plant ACP protein sequences showed that GmACP was classified in a legume-specific clade. Quantitative reverse-transcription polymerase chain reaction analysis demonstrated that GmACP was expressed in all soybean tissues but showed higher transcript accumulation in nodule tissue. RNA interference-mediated gene silencing of GmACP resulted in a significant reduction in nodule numbers on soybean transgenic roots. Fluorescent protein-labeled GmACP was localized to plastids in planta, the site of de novo fatty acid biosynthesis in plants. Analysis of the fatty acid content of root tissue silenced for GmACP expression, as determined by gas chromatography-mass spectrometry, showed an approximately 22% reduction, specifically in palmitic and stearic acid. Taken together, our data provide evidence that GmACP plays an important role in nodulation.

Genome-wide association study dissects the genetic architecture of oil biosynthesis in maize kernels

Maize kernel oil is a valuable source of nutrition. Here we extensively examine the genetic architecture of maize oil biosynthesis in a genome-wide association study using 1.03 million SNPs characterized in 368 maize inbred lines, including 'high-oil' lines. We identified 74 loci significantly associated with kernel oil concentration and fatty acid composition (P < 1.8 × 10(-6)), which we subsequently examined using expression quantitative trait loci (QTL) mapping, linkage mapping and coexpression analysis. More than half of the identified loci localized in mapped QTL intervals, and one-third of the candidate genes were annotated as enzymes in the oil metabolic pathway. The 26 loci associated with oil concentration could explain up to 83% of the phenotypic variation using a simple additive model. Our results provide insights into the genetic basis of oil biosynthesis in maize kernels and may facilitate marker-based breeding for oil quantity and quality.

Feedback regulation of plastidic acetyl-CoA carboxylase by 18:1-acyl carrier protein in Brassica napus

Plant seed oil represents a major renewable source of reduced carbon, but little is known about the biochemical regulation of its synthesis. The goal of this research was to identify potential feedback regulation of fatty acid biosynthesis in Brassica napus embryo-derived cell cultures and to characterize both the feedback signals and enzymatic targets of the inhibition. Fatty acids delivered via Tween esters rapidly reduced the rate of fatty acid synthesis in a dose-dependent and reversible manner, demonstrating the existence of feedback inhibition in an oil-accumulating tissue. Tween feeding did not affect fatty acid elongation in the cytosol or the incorporation of radiolabeled malonate into nascent fatty acids, which together pinpoint plastidic acetyl-CoA carboxylase (ACCase) as the enzymatic target of feedback inhibition. To identify the signal responsible for feedback, a variety of Tween esters were tested for their effects on the rate of fatty acid synthesis. Maximum inhibition was achieved upon feeding oleic acid (18:1) Tween esters that resulted in the intracellular accumulation of 18:1 free fatty acid, 18:1-CoA, and 18:1-acyl-carrier protein (ACP). Direct, saturable inhibition of ACCase enzyme activity was observed in culture extracts and in extracts of developing canola seeds supplemented with 18:1-ACP at physiological concentrations. A mechanism for feedback inhibition is proposed in which reduced demand for de novo fatty acids results in the accumulation of 18:1-ACP, which directly inhibits plastidic ACCase, leading to reduced fatty acid synthesis. Defining this mechanism presents an opportunity for mitigating feedback inhibition of fatty acid synthesis in crop plants to increase oil yield.

Plant lipids: metabolism, mutants, and membranes

The mechanisms that regulate plant lipid metabolism determine the dietary and industrial value of storage oils found in economically important species and may control the ability of many plants to survive exposure to temperature extremes. Many of the problems researchers have in defining the pathways, enzymes, and genes involved in plant lipid metabolism appear to be amenable to analysis by genetic approaches. Mutants with alterations in membrane lipid composition have also been used to study the structural and adaptive roles of lipids. The application of genetic engineering methods affords opportunities for researchers to apply knowledge gained about plant lipid metabolism toward enhanced use of plant oils as abundant and renewable sources of reduced carbon.

Fatty acid and lipid biosynthetic genes are expressed at constant molar ratios but different absolute levels during embryogenesis

In plants, fatty acid and complex lipid synthesis requires the correct spatial and temporal activity of many gene products. Quantitative northern analysis showed that mRNA for the biotin carboxylase subunit of heteromeric acetyl-coenzyme A carboxylase, fatty acid synthase components (3-oxoacyl-acyl carrier protein [ACP] reductase, enoyl-ACP reductase, and acyl-ACP thioesterase), and stearoyl-ACP desaturase accumulate in a coordinate manner during Brassica napus embryogenesis. The mRNAs were present in a constant molar stoichiometric ratio. Transcript abundance of mRNAs for the catalytic proteins was found to be similar, whereas the number of ACP transcripts was approximately 7-fold higher. The peak of mRNA accumulation of all products was between 20 and 29 d after flowering; by 42 d after flowering, the steady-state levels of all transcripts fell to about 5% of their peak levels, which suggests that the mRNAs have similar stability and kinetics of synthesis. Biotin carboxylase was found to accumulate to a maximum of 59 fmol mg(-1) total RNA in embryos, which is in general agreement with the value of 170 fmol mg(-1) determined for Arabidopsis siliques (J.S. Ke, T.N. Wen, B.J. Nikolau, E.S. Wurtele [2000] Plant Physiol 122: 1057-1071). Embryos accumulated between 3- and 15-fold more transcripts per unit total RNA than young leaf tissue; the lower quantity of leaf 3-oxoacyl-ACP reductase mRNA was confirmed by reverse transcriptase-polymerase chain reaction. This is in conflict with analysis of B. napus transcripts using an Arabidopsis microarray (T. Girke, J. Todd, S. Ruuska, J. White, C. Benning, J. Ohlrogge [2000] Plant Physiol 124: 1570-1581) where similar leaf to seed levels of fatty acid synthase component mRNAs were reported.

Overexpression of acyl carrier protein-1 alters fatty acid composition of leaf tissue in Arabidopsis

Acyl carrier protein (ACP) is a small (9 kD) acidic protein that is an essential cofactor in plant fatty acid biosynthesis. Most plants have several isoforms of ACP, some of which are expressed constitutively and others that appear to be more tissue specific. Although the critical role of ACP in fatty acid biosynthesis has been established, the role of the diverse number of isoforms has yet to be elucidated. We have generated transgenic Arabidopsis plants that express high levels of ACP-1, a seed-predominant ACP isoform, in leaf tissue under control of the cauliflower mosaic virus 35S promoter. Western and northern analysis of these plants demonstrate 3- to 8-fold increased expression of this isoform in leaf tissue, but no significant changes in seed. Analysis of the fatty acid composition of leaf tissue revealed that overexpression of ACP-1 in leaf tissue alters fatty acid composition. Significant decreases in levels of 16:3 were noted along with increases in 18:3. These findings represent the first in vivo report that overexpression of an ACP isoform results in changes in fatty acid composition in plants.

Identification of a cotton fiber-specific acyl carrier protein cDNA by differential display

Transcripts from immature fibers and stripped ovules (fibers removed) of cotton (Gossypium hirsutum L.) were compared by differential display to identify cDNA fragments that represent mRNAs that are expressed primarily in cotton fibers. Eight independent fiber-specific cDNA fragments were isolated. One of these cDNAs had strong sequence similarity with acyl carrier protein (ACP). A full-length cDNA for the cotton fiber-specific ACP was isolated using a PCR cDNA library screening technique. This 713 bp cDNA has an open reading frame that encodes a 136 amino acid polypeptide. Overall nucleotide and amino acid sequence identities with other plant ACP gene sequences averaged 66% and 60% respectively. A 19 amino acid sequence surrounding the prosthetic group attachment site is nearly identical to other plant ACP genes. Northern blot analyses showed that transcripts homologous to this fiber-specific ACP cDNA were predominantly expressed during the elongation stage of fiber development. Initial genomic Southern blot analysis indicated that a single copy of the fiber-specific ACP gene may be present in both the cotton A and D genomes, since diploid Gossypium species with A or D genomes gave identical bands. We speculate that this putative fiber-specific ACP may play an important role in rapidly elongating cotton fibers by contributing to the synthesis of membrane lipids. It is also apparent that during the evolution of cotton a member of the ACP gene family has been recruited for specific expression in cotton fibers.

Characterization of the polyketide synthase gene (pksL1) required for aflatoxin biosynthesis in Aspergillus parasiticus

Aflatoxins are potent toxic and carcinogenic compounds, produced by Aspergillus parasiticus and A. flavus as secondary metabolites. In this research, a polyketide synthase gene (pksL1), the key gene for aflatoxin biosynthesis initiation in A. parasiticus, has been functionally identified and molecularly characterized. PCR-derived DNA probes were used to find the pksL1 gene from subtracted, aflatoxin-related clones. Gene knockout experiments generated four pksL1 disruptants which lost both the ability to produce aflatoxins B1, B2, and G1 and the ability to accumulate norsolorinic acid and all other intermediates of the aflatoxin biosynthetic pathway. A pksL1 DNA probe detected a 6.6-kb poly(A)+ RNA transcript in Northern (RNA) hybridizations. This transcript, associated with aflatoxin production, exhibited a regulated expression that was influenced by growth phase, medium composition, and culture temperature. DNA sequencing of pksL1 revealed an open reading frame for a polypeptide (PKSL1) of 2,109 amino acids. Sequence analysis further recognized four functional domains in PKSL1, acyl carrier protein, beta-ketoacyl-acyl carrier protein synthase, acyltransferase, and thioesterase, all of which are usually present in polyketide synthases and fatty acid synthases. On the basis of these results, we propose that pksL1 encodes the polyketide synthase which synthesizes the backbone polyketide and initiates aflatoxin biosynthesis. In addition, the transcript of pksL1 exhibited heterogeneity at the polyadenylation site similar to that of plant genes.

Molecular cloning and sequence analysis of a seed-expressed acyl carrier protein (ACP) gene from Brassica campestris (Agrani)

We describe here the nucleotide sequence of the Brassica campestris ACPSF1 gene which encodes a seed-expressed acyl carrier protein (ACP). The 3600 bp sequence consists of 1740 bp upstream of the translation start codon, 828 bp spanning the coding region which is interrupted by three introns and 1032 bp downstream of the stop codon. Using a ACPSF1 gene-specific probe, transcripts could be detected in developing seeds, but not in leaves. The gene is now the only known member that represents group I seed-expressed ACP multigene family of Brassica species. The 5' flanking sequence of the ACPSF1 gene was examined for putative transcriptional regulatory elements. A sequence alignment of the 5' flanking regions of the available seed-expressed ACP genes of Brassica species showed some conserved regions which might have some common regulatory significance.

Identification of domains in an Arabidopsis acyl carrier protein gene promoter required for maximal organ-specific expression

Deletions were made in the promoter of the acyl carrier protein (ACP) Acll.2 gene from Arabidopsis to investigate the nature of the cis-acting elements that direct its expression. These constructs, which included the untranslated leader region, were fused to a reporter gene coding for beta-glucuronidase (GUS) and transformed into tobacco. Quantitative fluorometric analysis of GUS activity in transgenic plants showed that expression in young leaves drops to a basal level when a 85 bp domain, from -320 to -236 relative to transcription initiation, is deleted. Maximum promoter activity in roots also depends on this domain, but two other regions are also important. In total, deletion of the sequences from -466 to -55 caused an ca. 80-fold reduction in Acl1.2 promoter activity in roots. The -320 to -236 domain forms a complex with a protein factor found in leaves and roots, which was not detectable in seeds. The formation of this protein-DNA complex was abolished by mutation of a bZIP core motif, ACGT, found within the context AAGACGTAG, which is dissimilar to the other bZIP-binding sites thus far characterized in plants. Previously we showed that Acl1.2 promoter activity is highest in seeds [2]. Here we find, in contrast to leaves and roots, that deletion to position -236 has no effect on GUS levels in seeds. However, nearly a 100-fold drop was observed when the -235 to -55 region was removed. Hence, this 180 bp domain contains all the cis-acting information necessary for Acl1.2 promoter activity in seeds. The same region is necessary for Acl1.2 activity in the receptacle, stigma, tapetum and pollen of the flower, as demonstrated by histochemical staining.

Avenacosidase from oat: purification, sequence analysis and biochemical characterization of a new member of the BGA family of beta-glucosidases

A protein consisting of 60 kDa subunits (As-P60) was isolated from etiolated oat seedlings (Avena sativa L.) and characterized as avenacosidase, a beta-glucosidase that belongs to a preformed defence system of oat against fungal infection. The enzyme is highly aggregated; it consists of 300-350 kDa aggregates and multimers thereof. Dissociation by freezing/thawing leads to complete loss of enzyme activity. The specificity of the enzyme was investigated with para-nitrophenyl derivatives which serve as substrates, in decreasing order beta-fucoside, beta-glucoside, beta-galactoside, beta-xyloside. The corresponding orthonitrophenyl glycosides are less well accepted. No hydrolysis was found with alpha-glycosides and beta-thioglucoside. An anti-As-P60 antiserum was prepared and used for isolation of a cDNA clone coding for As-P60. A presequence of 55 amino acid residues was deduced from comparison of the cDNA sequence with the N-terminal sequence determined by Edman degradation of the mature protein. The presequence has the characteristics of a stroma-directing signal peptide; localization of As-P60 in plastids of oat seedlings was confirmed by western blotting. The amino acid sequence revealed significant homology (> 39% sequence identity) to beta-glucosidases that are constituents of a defence mechanism in dicotyledonous plants. 34% sequence identity was even found with mammalian and bacterial beta-glucosidases of the BGA family. Avenacosidase extends the occurrence of this family of beta-glucosidases to monocotyledonous plants.

Isolation and characterization of two Brassica napus embryo acyl-ACP thioesterase cDNA clones

Acyl-ACP thioesterases are involved in regulating chain termination of fatty acid biosynthesis in plant systems. Previously, acyl-ACP thioesterase purified from Brassica napus seed tissue has been shown to have a high preference for hydrolysing oleoyl-ACP. Here, oligonucleotides derived from B. napus oleoyl-ACP thioesterase protein sequence data have been used to isolate two acyl-ACP thioesterase clones from a B. napus embryo cDNA library. The two clones, pNL2 and pNL3, contain 1642 bp and 1523 bp respectively and differ in the length of their 3' non-coding regions. Both cDNAs contain open reading frames of 366 amino acids which encode for 42 kDa polypeptides. Mature rape thioesterase has an apparent molecular weight of 38 kDa on SDS-PAGE and these cDNAs therefore encode for precursor forms of the enzyme. This latter finding is consistent with the expected plastidial location of fatty acid synthase enzymes. Northern blot analysis shows thioesterase mRNA size to be ca. 1.6 kb and for the thioesterase genes to be highly expressed in seed tissue coincident with the most active phase of storage lipid synthesis. There is some sequence heterogeneity between the two cDNA clones, but overall they are highly homologous sharing 95.7% identity at the DNA level and 98.4% identity at the amino acid level. Some sequence heterogeneity was also observed between the deduced and directly determined thioesterase protein sequences. Consistent with the observed sequence heterogeneity was Southern blot data showing B. napus thioesterase to be encoded by a small multi-gene family.

Regulated expression of the rat medium chain hydrolase gene in transgenic rape seed

Medium chain hydrolase (MCH) is an enzyme which regulates the chain length of fatty acid synthesis specifically in the mammary gland of the rat. During lactation, MCH interacts with fatty acid synthase (FAS) to cause premature release of acyl chains, thus providing medium chain fatty acids for synthesis of milk fat. In this study we have investigated the ability of rat MCH to interact with the phylogenetically more distant FAS structure present in plant systems and to cause a perturbation of fatty acid synthesis. In in vitro experiments, addition of purified MCH to rapeseed homogenates was found to cause a significant perturbation of fatty acid synthesis towards medium chain length products. The rat MCH gene was expressed in transgenic oilseed rape using a seed specific rape acyl carrier protein (ACP) promoter and a rape ACP plastid targeting sequence. Western analysis showed MCH protein to be present in transgenic seed and for its expression to be developmentally regulated in concert with storage lipid synthesis. The chimaeric preprotein was correctly processed and immunogold labelling studies confirmed MCH to be localized within plastid organelles. However, fatty acid analysis of oil from MCH-expressing rape seed showed no significant differences to that from control seed.

Developmental regulation of an acyl carrier protein gene promoter in vegetative and reproductive tissues

The expression of an Arabidopsis acyl carrier protein (ACP) gene promoter has been examined in transgenic tobacco plants by linking it to the reporter gene beta-glucuronidase (GUS). Fluorometric analysis showed that the ACP gene promoter was most active in developing seeds. Expression was also high in roots, but significantly lower in young leaves and downregulated upon their maturation. Etiolated and light-grown seedlings showed the same level of GUS activity, indicating that this promoter is not tightly regulated by light. Histochemical studies revealed that expression was usually highest in apical/meristematic zones of vegetative tissues. Young flowers (ca. 1 cm in length) showed GUS staining in nearly all cell types, however, cell-specific patterns emerged in more mature flowers. The ACP gene promoter was active in the stigma and transmitting tissue of the style, as well as in the tapetum of the anther, developing pollen, and ovules. The results provide evidence that this ACP gene is regulated in a complex manner and is responsive to the array of signals which accompany cell differentiation, and a demand for fatty acids and lipids, during organogenesis.

Isolation and characterization of a cDNA from Cuphea lanceolata encoding a beta-ketoacyl-ACP reductase

A cDNA encoding beta-ketoacyl-ACP reductase (EC 1.1.1.100), an integral part of the fatty acid synthase type II, was cloned from Cuphea lanceolata. This cDNA of 1276 bp codes for a polypeptide of 320 amino acids with 63 N-terminal residues presumably representing a transit peptide and 257 residues corresponding to the mature protein of 27 kDa. The encoded protein shows strong homology with the amino-terminal sequence and two tryptic peptides from avocado mesocarp beta-ketoacyl-ACP reductase, and its total amino acid composition is highly similar to those of the beta-ketoacyl-ACP reductases of avocado and spinach. Amino acid sequence homologies to polyketide synthase, beta-ketoreductases and short-chain alcohol dehydrogenases are discussed. An engineered fusion protein lacking most of the transit peptide, which was produced in Escherichia coli, was isolated and proved to possess beta-ketoacyl-ACP reductase activity. Hybridization studies revealed that in C. lanceolata beta-ketoacyl-ACP reductase is encoded by a small family of at least two genes and that members of this family are expressed in roots, leaves, flowers and seeds.

Molecular cloning of higher-plant 3-oxoacyl-(acyl carrier protein) reductase. Sequence identities with the nodG-gene product of the nitrogen-fixing soil bacterium Rhizobium meliloti

cDNA clones encoding the fatty-acid- biosynthetic enzyme NADPH-linked 3-oxoacyl-(acyl carrier protein) (ACP) reductase were isolated from a Brassica napus (rape) developing seed library and from an Arabidopsis thaliana (thale cress) leaf library. The N-terminal end of the coding region shows features typical of a stromal-targeting plastid-transit peptide. The deduced amino acid sequences have 41% and 55% identity respectively with the nodG-gene product of Rhizobium meliloti, one of the host-specific genes that restrict infectivity of this bacterium to a small range of host plants. The probability that the nodG-gene product is a oxoreductase strengthens the hypothesis that some of the host-specific nod-gene products are enzymes which synthesize polyketides that uniquely modify the Rhizobium nodulation signal molecule.

3-Oxoacyl-[ACP] reductase from oilseed rape (Brassica napus)

3-Oxoacyl-[ACP] reductase (E.C. 1.1.1.100, alternatively known as beta-ketoacyl-[ACP] reductase), a component of fatty acid synthetase has been purified from seeds of rape by ammonium sulphate fractionation, Procion Red H-E3B chromatography, FPLC gel filtration and high performance hydroxyapatite chromatography. The purified enzyme appears on SDS-PAGE as a number of 20-30 kDa components and has a strong tendency to exist in a dimeric form, particularly when dithiothreitol is not present to reduce disulphide bonds. Cleveland mapping and cross-reactivity with antiserum raised against avocado 3-oxoacyl-[ACP] reductase both indicate that the multiple components have similar primary structures. On gel filtration the enzyme appears to have a molecular mass of 120 kDa suggesting that the native structure is tetrameric. The enzyme has a strong preference for the acetoacetyl ester of acyl carrier protein (Km = 3 microM) over the corresponding esters of the model substrates N-acetyl cysteamine (Km = 35 mM) and CoA (Km = 261 microM). It is inactivated by dilution but this can be partly prevented by the inclusion of NADPH. Using an antiserum prepared against avocado 3-oxoacyl-[ACP] reductase, the enzyme has been visualised inside the plastids of rape embryo and leaf tissues by immunoelectron microscopy. Amino acid sequencing of two peptides prepared by digestion of the purified enzyme with trypsin showed strong similarities with 3-oxoacyl-[ACP] reductase from avocado pear and the Nod G gene product from Rhizobium meliloti.

The isolation and functional characterisation of a B. napus acyl carrier protein 5' flanking region involved in the regulation of seed storage lipid synthesis

Acyl carrier protein (ACP) is a key component of the fatty acid biosynthetic machinery in plants. A 1.4 kb 5' flanking region of a Brassica napus ACP gene (ACP05) was transcriptionally fused to the reporter gene beta-glucuronidase (GUS), and expression of the chimeric gene monitored in transgenic tobacco. GUS activity was found to increase through seed development reaching a maximum value, coincident with the most active phase of storage lipid synthesis that was, on average, 100-fold higher than that observed in leaf. In control plants transformed with CaMV 35S-GUS constructs, GUS activity was similar in leaf and all stages of seed development. Based on average values, the level of GUS expression obtained via the ACP promoter was comparable to that obtained from the CaMV 35S promoter. We therefore conclude that the isolated 5' ACP flanking sequence represents a strong promoter element involved in the developmental regulation of storage lipid synthesis in B. napus seed tissue. Putative regulatory elements in the 5' upstream region of ACP05 were identified by dot matrix analysis and by sequence comparison with the upstream regions from a second seed-expressed rape ACP gene and from an Arabidopsis ACP gene.

Organization of the enzymatic domains in the multifunctional polyketide synthase involved in erythromycin formation in Saccharopolyspora erythraea

Localization of the enzymatic domains in the three multifunctional polypeptides from Saccharopolyspora erythraea involved in the formation of the polyketide portion of the macrolide antibiotic erythromycin was determined by computer-assisted analysis. Comparison of the six synthase units (SU) from the eryA genes with each other and with mono- and multifunctional fatty acid and polyketide synthases established the extent of each beta-ketoacyl acyl-carrier protein (ACP) synthase, acyltransferase, beta-ketoreductase, ACP, and thioesterase domain. The extent of the enoyl reductase (ER) domain was established by detecting similarity to other sequences in the database. A segment containing the putative dehydratase (DH) domain in EryAII, with a potential active-site histidine residue, was also found. The finding of conservation of a portion of the DH-ER interdomain region in the other five SU, which lack these two functions, suggests a possible evolutionary path for the generation of the six SU.

The barley genes Acl1 and Acl3 encoding acyl carrier proteins I and III are located on different chromosomes

Acyl carrier protein (ACP) is an essential cofactor for plant fatty acid synthesis. Three isoforms occur in barley seedling leaves. The genes Acl1 and Acl3 coding for the predominant ACP I and the minor ACP III, respectively, have been cloned and characterized as has a full-length cDNA for ACP III. Both genes, extending over more than 2.5 kb, have a conserved mosaic structure of four exons and three introns which result in mRNAs of ca. 900 bases. Alignment of the DNA sequences demonstrates that homology is restricted to the two exons coding for the mature protein whereas the remaining segments of the genes including the transit peptide-coding domains lack homology. Southern blot analyses demonstrate that Acl1 and Acl3 represent single copy genes located on chromosomes 7 and 1, respectively. Primer extension analyses identified multiple transcription start sites in both genes. The promoter regions are remarkably different; that of Acl3 resembles those for mammalian housekeeping genes in having a high G + C content plus three copies of an RNA polymerase II recognition GC element and in lacking correctly positioned TATA boxes. These features are in accordance with the hypothesis that Acl1 is specifically expressed in leaf tissue whereas Acl3 is a constitutively expressed gene.

Biosynthesis of the Escherichia coli siderophore enterobactin: sequence of the entF gene, expression and purification of EntF, and analysis of covalent phosphopantetheine

The sequence of the entF gene which codes for the serine activating enzyme in enterobactin biosynthesis is reported. The gene encodes a protein with a calculated molecular weight of 142,006 and shares homologies with the small subunits of gramicidin S synthetase and tyrocidine synthetase. We have subcloned and overexpressed entF in a multicopy plasmid and attempted to demonstrate L-serine-dependent ATP-[32P]PPi exchange activity and its participation in enterobactin biosynthesis, but the overexpressed enzyme appears to be essentially inactive in crude extract. A partial purification of active EntF from wild-type Escherichia coli, however, has confirmed the expected activities of EntF. In a search for possible causes for the low level of activity of the overexpressed enzyme, we have discovered that EntF contains a covalently bound phosphopantetheine cofactor.

Purification and characterization of acyl carrier protein from two cyanobacteria species

The acyl carrier protein (ACP), an essential protein cofactor for fatty acid synthesis, has been isolated from two cyanobacteria: the filamentous, heterocystous, Anabaena variabilis (ATCC 29211) and the unicellular Synechocystis 6803 (ATCC 27184). Both ACPs have been purified to homogeneity utilizing a three-column procedure. Synechocystis 6803 ACP was purified 1800-fold with 67% yield, while A. variabilis ACP was purified 1040-fold with 50% yield. Yields of 13.0 micrograms ACP/g Synechocystis 6803 and 9.0 micrograms ACP/g A. variabilis were achieved. Amino acid analysis indicated that these ACPs were highly charged acidic proteins similar to other known ACPs. Sequence analysis revealed that both cyanobacterial ACPs were highly conserved with both spinach and Escherichia coli ACP at the phosphopantetheine prosthetic group region. Examining the probability of alpha-helix and beta-turn regions in various ACPs, showed that cyanobacterial ACPs were more closely related to E. coli ACP than spinach ACP I. Immunoblot analysis and a competitive binding assay for ACP illustrated that both ACPs bound poorly to spinach ACP I antibody. SDS/PAGE and native PAGE of Synechocystis 6803 ACP and A. variabilis ACP showed that cyanobacteria ACPs co-migrated with E. coli ACP and had relative molecular masses of 18,100 and 17,900 respectively. Both native and urea gel analysis of acyl-ACP products from fatty acid synthase reactions demonstrated that bacterial ACPs and plant ACP gave essentially the same metabolic products when assayed using either bacterial or plant fatty acid synthase. A. variabilis and Synechocystis 6803 ACP could be acylated using E. coli acyl ACP synthetase.

Immunological detection of NADH-specific enoyl-ACP reductase from rape seed (Brassica napus)--induction, relationship of alpha and beta polypeptides, mRNA translation and interaction with ACP

An antibody has been raised against rape seed enoyl-ACP reductase. This recognizes both the alpha and beta polypeptides of the enzyme. Immunoblotting of fresh seed demonstrates that beta is not present in seed material, and that it is produced by proteolysis during isolation. It is thus deduced that rape seed enoyl reductase is an alpha 4 homotetramer. Leaf material from both rape and Arabidopsis have an enoyl reductase with a similar electrophoretic mobility to the rape seed enzyme when analyzed on SDS-PAGE. Quantitative immunoassay has demonstrated that the enzyme continually increases during lipid deposition, indicating that an increase in this enzyme is required to sustain high levels of lipid biosynthesis. In vitro translation experiments show that the enzyme is nuclear coded and synthesized as a precursor form. Immunogold electron microscopy has demonstrated that enoyl reductase is located in plastids. It is shown that ACP-Sepharose may be used as a matrix in the purification of enoyl-ACP reductase.

A conserved cleavage-site motif in chloroplast transit peptides

A collection of 32 stroma-targeting chloroplast transit peptides with known cleavage sites have been analysed in terms of amino acid preferences in the vicinity of the processing site. A loosely conserved consensus motif (Val/Ile)-X-(Ala/Cys) decreases Ala is found in the majority of the transit peptides. About 30% of the sequences have a perfect match to the consensus. When such a match is found, there is a 90% probability that it specifies the correct cleavage site.

Evolutionary and tissue-specific control of expression of multiple acyl-carrier protein isoforms in plants and bacteria

We have examined the occurrence of multiple acyl-carrier protein (ACP), isoforms in evolutionarily diverse species of higher and lower plants. Isoforms were resolved by native polyacrylamide gel electrophoresis (PAGE), and were detected by Western blotting or fluorography of [(3)H]-palmitate-labelled ACPs. Multiple isoforms of ACP were found in leaf tissue of the monocotyledons Avena sativa and Hordeum vulgare and dicotyledons Arabidopsis thaliana, Cuphea wrightii, and Brassica napus. Lower vascular plants including the lycopod Selaginella krausseriana, the gymnosperms Ephedra sp. and Dioon edule, the ferns Davallia feejensis and Marsilea sp. and the most primitive known extant vascular plant, Psilotum nudum, were all found to have multiple ACP isoforms, as were the nonvascular liverworts, Lunularia sp. and Marchantia sp. and the moss, Polytrichum sp. Therefore, the development of ACP isoforms appears to have occurred early in plant evolution. However, we could detect only a single electrophoretic form of ACP in the unicellular algae Chlamydomonas reinhardtii and Dunaliella tertiolecta and the photosynthetic cyanobacteria Synechocystis strain 6803 and Agmnellum quadruplicatum. Thus, multiple forms of ACP do not occur in all photosynthetic organisms but may be associated with multicellular plants. We have also examined tissue specificity and light control over the expression of ACP isoforms. The relative abundance of multiple forms of ACP in leaf of Spinacia and Avena was altered very little by light. Rather, the different patterns of ACP isoforms were primarily dependent on the tissue type.

Site-directed mutagenesis of the spinach acyl carrier protein-I prosthetic group attachment site

Site-directed mutagenesis was used to change the phosphopantetheine attachment site (Ser38) of spinach acyl carrier protein I (ACP-I) from a serine to a threonine or cysteine residue. 1. Although the native ACP-I is fully phosphopantethenylated when expressed in Escherichia coli, the TH-ACP-I and CY-ACP-I mutants were found to be completely devoid of the phosphopantetheine group. Therefore, the E. coli holoACP synthase requires serine for in vivo phosphopantetheine addition to spinach ACP-I. 2. Spinach holoACP synthase was completely inactive in vitro with either the TH-ACP-I or CY-ACP-I mutants. In addition, TH-ACP-I and CY-ACP-I were strong inhibitors of spinach holoACP synthase. 3. The mutant ACPs were weak or ineffective as inhibitors of spinach fatty acid synthesis and spinach oleoyl-ACP hydrolase. 4. Compared to holoACP-I, the mutant apoACP-I analogs had: (a) altered mobility in SDS and native gel electrophoresis, (b) altered binding to anti-(spinach ACP-I) antibodies and (c) altered isoelectric points. The combined physical, immunological and enzyme inhibition data indicate that attachment of the phosphopantheine prosthetic group alters ACP conformation.