A third fatty acid delta9-desaturase from Mortierella alpina with a different substrate specificity to ole1p and ole2p

Metabolic engineering of oleaginous yeast in the lipogenic phase enhances production of nervonic acid

Insufficient biosynthesis efficiency during the lipogenic phase can be a major obstacle to engineering oleaginous yeasts to overproduce very long-chain fatty acids (VLCFAs). Taking nervonic acid (NA, C24:1) as an example, we overcame the bottleneck to overproduce NA in an engineered Rhodosporidium toruloides by improving the biosynthesis of VLCFAs during the lipogenic phase. First, evaluating the catalytic preferences of three plant-derived ketoacyl-CoA synthases (KCSs) rationally guided reconstructing an efficient NA biosynthetic pathway in R. toruloides. More importantly, a genome-wide transcriptional analysis endowed clues to strengthen the fatty acid elongation (FAE) module and identify/use lipogenic phase-activated promoter, collectively addressing the stagnation of NA accumulation during the lipogenic phase. The best-designed strain exhibited a high NA content (as the major component in total fatty acid [TFA], 46.3%) and produced a titer of 44.2 g/L in a 5 L bioreactor. The strategy developed here provides an engineering framework to establish the microbial process of producing valuable VLCFAs in oleaginous yeasts.

Lipid metabolism research in oleaginous fungus Mortierella alpina: Current progress and future prospects

The oleaginous fungus Mortierella alpina has distinct advantages in long-chain PUFAs production, and it is the only source for dietary arachidonic acid (ARA) certificated by FDA and European Commission. This review provides an overall introduction to M. alpina, including its major research methods, key factors governing lipid biosynthesis, metabolic engineering and omics studies. Currently, the research interests in M. alpina focus on improving lipid yield and fatty acid desaturation degree by enhancing fatty acid precursors and the reducing power NADPH, and genetic manipulation on PUFAs synthetic pathways is carried to optimise fatty acid composition. Besides, multi-omics studies have been applied to elucidate the global regulatory mechanism of lipogenesis in M. alpina. However, research challenges towards achieving a lipid cell factory lie in strain breeding and cost control due to the coenocytic mycelium, long fermentation period and insufficient conversion rate from carbon to lipid. We also proposed future research goals based on a multilevel regulating strategy: obtaining ideal chassis by directional evolution and high-throughput screening; rewiring central carbon metabolism and inhibiting competitive pathways by multi-gene manipulation system to enhance carbon to lipid conversion rate; optimisation of protein function based on post-translational modification; application of dynamic fermentation strategies suitable for different fermentation phases. By reviewing the comprehensive research progress of this oleaginous fungus, we aim to further comprehend the fungal lipid metabolism and provide reference information and guidelines for the exploration of microbial oils from the perspectives of fundamental research to industrial application.

Membrane-bound Δ12 fatty acid desaturase (FAD12); From Brassica napus to E. coli expression system

Fatty acid desaturase catalyzes the desaturation reactions by insertion of double bonds into the fatty acyl chain, producing unsaturated fatty acids. Though soluble fatty acid desaturases have been studied widely in advanced organisms, there are very limited studies of membrane fatty acid desaturases due to the difficulty of generating recombinant desaturase. Brassica napus is a rapeseed, which possesses a range of different membrane-bound desaturases capable of producing fatty acids including Δ3, Δ4, Δ8, Δ9, Δ12, and Δ15 fatty acids. The 1155 bp open reading frame of Δ12 fatty acid desaturase (FAD12) from Brassica napus codes for 383 amino acid residues with a molecular weight of 44 kDa. It was expressed in Escherichia coli at 37 °C in soluble and insoluble forms when induced with 0.5 mM IPTG. Soluble FAD12 has been purified using Ni²⁺-Sepharose affinity chromatography with a total protein yield of 0.728 mg/mL. Gas chromatography-mass spectrometry (GC-MS) analysis revealed that desaturase activity of FAD12 could produce linoleic acid from oleic acid at a retention time of 17.6 with a conversion rate of 47%. Characterization of purified FAD12 revealed the optimal temperature of FAD12 was 50 °C with 2 mM preferred substrate concentration of oleic acid. Analysis of circular dichroism (CD) showed FAD12 was made up of 47.3% and 0.9% of alpha-helix and β-sheet secondary structures. The predicted Tm value was 50.2 °C.

Membrane fluidity is involved in the regulation of heat stress induced secondary metabolism in Ganoderma lucidum

Ganoderma lucidum has become a potential model system for evaluating how environmental factors regulate the secondary metabolism of basidiomycetes. Heat stress (HS) is one of the most important environmental factors. It was previously reported that HS could induce the biosynthesis of ganoderic acids (GA). In this study, we found that HS increased GA biosynthesis and also significantly increased cell membrane fluidity. Furthermore, our results showed that addition of the membrane rigidifier dimethylsulfoxide (DMSO) could revert the increased GA biosynthesis elicited by HS. These results indicate that an increase in membrane fluidity is associated with HS-induced GA biosynthesis. Further evidence showed that the GA content was decreased in D9des-silenced strains and could be reverted to WT levels by addition of the membrane fluidizer benzyl alcohol (BA). In contrast, GA content was increased in D9des-overexpression strains and could be reverted to WT levels by the addition of DMSO. Furthermore, both membrane fluidity and GA biosynthesis induced by HS could be reverted by DMSO in WT and D9des-silenced strains. To the best of our knowledge, this is the first report demonstrating that membrane fluidity is involved in the regulation of heat stress induced secondary metabolism in filamentous fungi.

Molecular Cloning and Functional Expression of a Δ9- Fatty Acid Desaturase from an Antarctic Pseudomonas sp. A3

Fatty acid desaturase enzymes play an essential role in the synthesis of unsaturated fatty acids. Pseudomonas sp. A3 was found to produce a large amount of palmitoleic and oleic acids after incubation at low temperatures. Using polymerase Chain Reaction (PCR), a novel Δ9- fatty acid desaturase gene was isolated, cloned, and successfully expressed in Escherichia coli. The gene was designated as PA3FAD9 and has an open reading frame of 1,185 bp which codes for 394 amino acids with a predicted molecular weight of 45 kDa. The activity of the gene product was confirmed via GCMS, which showed a functional putative Δ9-fatty acid desaturase capable of increasing the total amount of cellular unsaturated fatty acids of the E. coli cells expressing the gene. The results demonstrate that the cellular palmitoleic acids have increased two-fold upon expression at 15°C using only 0.1 mM IPTG. Therefore, PA3FAD9 from Pseudomonas sp.A3 codes for a Δ9-fatty acid desaturase-like protein which was actively expressed in E. coli.

Analysis of cytochrome b(5) reductase-mediated metabolism in the phytopathogenic fungus Zymoseptoria tritici reveals novel functionalities implicated in virulence

Septoria tritici blotch (STB) caused by the Ascomycete fungus Zymoseptoria tritici is one of the most economically damaging diseases of wheat worldwide. Z. tritici is currently a major target for agricultural fungicides, especially in temperate regions where it is most prevalent. Many fungicides target electron transfer enzymes because these are often important for cell function. Therefore characterisation of genes encoding such enzymes may be important for the development of novel disease intervention strategies. Microsomal cytochrome b5 reductases (CBRs) are an important family of electron transfer proteins which in eukaryotes are involved in the biosynthesis of fatty acids and complex lipids including sphingolipids and sterols. Unlike the model yeast Saccharomyces cerevisiae which possesses only one microsomal CBR, the fully sequenced genome of Z. tritici bears three possible microsomal CBRs. RNA sequencing analysis revealed that ZtCBR1 is the most highly expressed of these genes under all in vitro and in planta conditions tested, therefore ΔZtCBR1 mutant strains were generated through targeted gene disruption. These strains exhibited delayed disease symptoms on wheat leaves and severely limited asexual sporulation. ΔZtCBR1 strains also exhibited aberrant spore morphology and hyphal growth in vitro. These defects coincided with alterations in fatty acid, sphingolipid and sterol biosynthesis observed through GC-MS and HPLC analyses. Data is presented which suggests that Z. tritici may use ZtCBR1 as an additional electron donor for key steps in ergosterol biosynthesis, one of which is targeted by azole fungicides. Our study reports the first functional characterisation of CBR gene family members in a plant pathogenic filamentous fungus. This also represents the first direct observation of CBR functional ablation impacting upon fungal sterol biosynthesis.

Cloning and functional expression of a cDNA encoding stearoyl-ACP Δ9-desaturase from the endosperm of coconut (Cocos nucifera L.)

Coconut (Cocos nucifera L.) is an economically tropical fruit tree with special fatty acid compositions. The stearoyl-acyl carrier protein (ACP) desaturase (SAD) plays a key role in the properties of the majority of cellular glycerolipids. In this paper, a full-length cDNA of a stearoyl-acyl carrier protein desaturase, designated CocoFAD, was isolated from cDNA library prepared from the endosperm of coconut (C. nucifera L.). An 1176 bp cDNA from overlapped PCR products containing ORF encoding a 391-amino acid (aa) protein was obtained. The coded protein was virtually identical and shared the homology to other Δ9-desaturase plant sequences (greater than 80% as similarity to that of Elaeis guineensis Jacq). The real-time fluorescent quantitative PCR result indicated that the yield of CocoFAD was the highest in the endosperm of 8-month-old coconut and leaf, and the yield was reduced to 50% of the highest level in the endosperm of 15-month-old coconut. The coding region showed heterologous expression in strain INVSc1 of yeast (Saccharomyces cerevisiae). GC-MS analysis showed that the levels of palmitoleic acid (16:1) and oleic acid (18:1) were improved significantly; meanwhile stearic acid (18:0) was reduced. These results indicated that the plastidial Δ9 desaturase from the endosperm of coconut was involved in the biosynthesis of hexadecenoic acid and octadecenoic acid, which was similar with other plants. These results may be valuable for understanding the mechanism of fatty acid metabolism and the genetic improvement of CocoFAD gene in palm plants in the future.

Structure determinants for the substrate specificity of acyl-CoA Δ9 desaturases from a marine copepod

In contrast to soluble acyl-ACP desaturases from plants, little is known about the structure-guiding principle underlying substrate specificity and regioselectivity of membrane-bound acyl-CoA desaturases from animals, mainly due to lack of the three-dimensional structure information. Here we report identification of two homologous membrane-bound acyl-CoA Δ9 desaturases (ChDes9-1 and ChDes9-2) from the marine copepod Calanus hyperboreus that accumulates more than 90% of total storage lipids in the form of wax esters. ChDes9-2 is a common Δ9 desaturase with substrate specificity to long chain fatty acid 18:0, while ChDes9-1 is a new type of Δ9 desaturase introducing a Δ9 double bond into a wide range of very long chain fatty acids ranging from 20:0 to 26:0. Reciprocal domain swapping and site-directed mutagenesis guided by the membrane topology revealed that presence or absence of an amphipathic and bulky residue, tyrosine, in the middle of the second transmembrane domain was important in determining the substrate specificity of the two desaturases. To examine the mechanistic structure for the substrate specificity, tyrosine-scanning mutagenesis was employed to systematically substitute the residues in the transmembrane domain of the very long chain desaturase. The results showed that the transmembrane domain formed an α-helix structure probably involved in formation of the substrate-binding pocket and the corresponding residue of the tyrosine likely resided at the critical position within the pocket mediating the interaction with the substrates, thereby specifying the chain length of the substrates.

Identification and functional analysis of delta-9 desaturase, a key enzyme in PUFA Synthesis, isolated from the oleaginous diatom Fistulifera

Oleaginous microalgae are one of the promising resource of nonedible biodiesel fuel (BDF) feed stock alternatives. Now a challenge task is the decrease of the long-chain polyunsaturated fatty acids (PUFAs) content affecting on the BDF oxidative stability by using gene manipulation techniques. However, only the limited knowledge has been available concerning the fatty acid and PUFA synthesis pathways in microalgae. Especially, the function of Δ9 desaturase, which is a key enzyme in PUFA synthesis pathway, has not been determined in diatom. In this study, 4 Δ(9) desaturase genes (fD9desA, fD9desB, fD9desC and fD9desD) from the oleaginous diatom Fistulifera were newly isolated and functionally characterized. The putative Δ(9) acyl-CoA desaturases in the endoplasmic reticulum (ER) showed 3 histidine clusters that are well-conserved motifs in the typical Δ(9) desaturase. Furthermore, the function of these Δ(9) desaturases was confirmed in the Saccharomyces cerevisiae ole1 gene deletion mutant (Δole1). All the putative Δ(9) acyl-CoA desaturases showed Δ(9) desaturation activity for C16∶0 fatty acids; fD9desA and fD9desB also showed desaturation activity for C18∶0 fatty acids. This study represents the first functional analysis of Δ(9) desaturases from oleaginous microalgae and from diatoms as the first enzyme to introduce a double bond in saturated fatty acids during PUFA synthesis. The findings will provide beneficial insights into applying metabolic engineering processes to suppressing PUFA synthesis in this oleaginous microalgal strain.

Characterization of three Δ9-fatty acid desaturases with distinct substrate specificity from an oleaginous fungus Cunninghamella echinulata

In oleaginous fungus Cunninghamella echinulata, Δ9-fatty acid desaturase introduces the first double bond into a saturated fatty acid. Three distinct genes, designated as d9dma, d9dmb and d9dmc, all encoding putative Δ9-fatty acid desaturases were isolated from this strain. The predicted proteins showed 79-87 % identity to other fungal Δ9-fatty acid desaturases. They all contain three conserved histidine boxes, C-terminal cytochrome b 5 fusion and four transmembrane domains characteristic of Δ9-desaturase. Each putative Δ9-desaturase gene from C. echinulata was able to complement the ole1 mutation in Saccharomyces cerevisiae L8-14C through heterologous expression. Analysis of the fatty acid composition of the transgenic yeast revealed that the conversion rates of 16:0 and 18:0 by D9DMA were obviously higher than those of D9DMB and D9DMC. In addition, D9DMA, D9DMB and D9DMC all had a substrate preference for 18:0 compared with 16:0. Of interest, D9DMA could saturate 12:0, 14:0, 16:0, 17:0, 18:0 and 20:0, while D9DMB saturated 14:0, 16:0, 17:0, 18:0 and 20:0. We also noticed that the transcriptional level of d9dma in C. echinulata was stimulated by cell growth but not by decline in temperature. In contrast, expression of d9dmb and d9dmc was regulated by neither cell growth nor decline in temperature in this strain.

Expression and purification of integral membrane fatty acid desaturases

Fatty acid desaturase enzymes perform dehydrogenation reactions leading to the insertion of double bonds in fatty acids, and are divided into soluble and integral membrane classes. Crystal structures of soluble desaturases are available; however, membrane desaturases have defied decades of efforts due largely to the difficulty of generating recombinant desaturase proteins for crystallographic analysis. Mortierella alpina is an oleaginous fungus which possesses eight membrane desaturases involved in the synthesis of saturated, monounsaturated and polyunsaturated fatty acids. Here, we describe the successful expression, purification and enzymatic assay of three M. alpina desaturases (FADS15, FADS12, and FADS9-I). Estimated yields of desaturases with purity >95% are approximately 3.5% (Ca. 4.6 mg/L of culture) for FADS15, 2.3% (Ca. 2.5 mg/L of culture) for FADS12 and 10.7% (Ca. 37.5 mg/L of culture) for FADS9-I. Successful expression of high amounts of recombinant proteins represents a critical step towards the structural elucidation of membrane fatty acid desaturases.

Involvement of Arabidopsis ACYL-COENZYME A DESATURASE-LIKE2 (At2g31360) in the biosynthesis of the very-long-chain monounsaturated fatty acid components of membrane lipids

The Arabidopsis (Arabidopsis thaliana) acyl-coenzyme A (CoA) desaturase-like (ADS) gene family contains nine genes encoding fatty acid desaturase-like proteins. The biological function of only one member of the family, fatty acid desaturase5 (AtADS3/FAD5, At3g15850), is known, and this gene encodes the plastidic palmitoyl-monogalactosyldiacylglycerol Δ7 desaturase. We cloned seven members of the gene family that are predicted not to have a chloroplast transit peptide and expressed them in the yeast Saccharomyces cerevisiae. All seven have previously undescribed desaturase activity on very-long-chain fatty acid (VLCFA) substrates and exhibit diverse regiospecificity, catalyzing introduction of double bonds relative to the methyl end of the molecule (n-x) at n-6 (AtADS4, At1g06350), n-7 (AtADS1.3, At1g06100 and AtADS4.2, At1g06360), n-9 (AtADS1, At1g06080 and AtADS2, At2g31360) or Δ9 (relative to the carboxyl end of the molecule) positions (AtADS1.2, At1g06090 and AtADS1.4, At1g06120). Through forward and reverse genetics it was shown that AtADS2 is involved in the synthesis of the 24:1(n-9) and 26:1(n-9) components (X:Y, where X is chain length and Y is number of double bonds) of seed lipids, sphingolipids, and the membrane phospholipids phosphatidylserine, and phosphatidylethanolamine. Plants deficient in AtADS2 expression showed no obvious phenotype when grown under normal growing conditions, but showed an almost complete loss of phosphatidylethanolamine(42:4), phosphatidylserine(42:4), dihydroxy-monohexosylceramide(42:2)-2, trihydroxy-monohexosylceramide(42:2)-3, and trihydroxy-glycosylinositolphosphoceramide(42:2)-3, lipid species that contain the VLCFA 24:1(n-9), and trihydroxy-glycosylinositolphosphoceramide(44:2)-3, a lipid containing 26:1(n-9). Acyl-CoA profiling of these plants revealed a major reduction in 24:1-CoA and a small reduction in 26:1-CoA. Overexpression of AtADS2 resulted in a substantial increase in the percentage of glycerolipid and sphingolipids species containing 24:1 and a dramatic increase in the percentage of very-long-chain monounsaturated fatty acids in the acyl-CoA pool. Plants deficient in AtADS1 expression had reduced levels of 26:1(n-9) in seed lipids, but no significant changes in leaf phospholipids or sphingolipids were observed. These findings indicate that the 24-carbon and 26-carbon monounsaturated VLCFAs of Arabidopsis result primarily from VLCFA desaturation, rather than by elongation of long chain monounsaturated fatty acids.

Filamentous fungi for production of food additives and processing aids

Filamentous fungi are metabolically versatile organisms with a very wide distribution in nature. They exist in association with other species, e.g. as lichens or mycorrhiza, as pathogens of animals and plants or as free-living species. Many are regarded as nature's primary degraders because they secrete a wide variety of hydrolytic enzymes that degrade waste organic materials. Many species produce secondary metabolites such as polyketides or peptides and an increasing range of fungal species is exploited commercially as sources of enzymes and metabolites for food or pharmaceutical applications. The recent availability of fungal genome sequences has provided a major opportunity to explore and further exploit fungi as sources of enzymes and metabolites. In this review chapter we focus on the use of fungi in the production of food additives but take a largely pre-genomic, albeit a mainly molecular, view of the topic.

Identification of a novel delta9-fatty acid desaturase gene and its promoter from oil-producing fungus Rhizopus arrhizus

Reverse Transcriptional Polymerase Chain Reaction (RT-PCR), Rapid Amplification of the cDNA ends (RACE) and Thermal asymmetric interlaced (TAIL)-PCR were used successfully to clone the open reading frame (1,377 bp) of delta9-fatty acid desaturase gene (named as RAD9) and its promoter region from oil-producing fungi Rhizopus arrhizus. Functional identification of the protein was done by sub-cloning RAD9 into the expression vector pYES2.0 to generate a recombinant plasmid pYRAD9, which was then subsequently transformed into Saccharomyces cerevisiae delta9-fatty acid desaturase mutation strain L8-14C to be expressed under the control of GAL1 promoter. The transformant containing RAD9 named as L8-14C-pYRAD9 could grow on the synthetic minimal medium plate with out oleic acid supplement. Fatty acid analysis also showed that the transformant contained 16:1 and 18:1. This indicated that pYRAD9 could successfully complement the mutation of L8-14C. Computational analysis of the nucleotide sequence of RAD9 promoter showed several basic transcriptional elements including a CAAT box, a GC box, a CACCC box, two TATA boxes and also several putative target-binding sites for transcription factors, which have been reported to be involved in the regulation of lipid metabolism. Preliminary functional analysis of this promoter in S. cerevisiae was done using lacZ report gene.

Spore germination in Mortierella alpina is associated with a transient depletion of arachidonic acid and induction of fatty acid desaturase gene expression

Mortierella alpina is an oleaginous filamentous fungus whose vegetative mycelium is known to accumulate triglyceride oil containing large amounts of arachidonic acid (ARA 20:4, n - 6). We report that the spores of Mortierella alpina also contain a large proportion of ARA, comprising 50% of total fatty acid. Fatty acid desaturase genes were not expressed in dormant spores but were induced during germination, following a significant drop in the level of ARA (down from 50% of total fatty acid to 12%) prior to germ-tube emergence. We propose that ARA serves as a reserve supply of carbon and energy that is utilised during the early stages of spore germination in Mortierella alpina.

Functional characterization of Δ9 and ω9 desaturase genes in Mortierella alpina 1S-4 and its derivative mutants

Cloning and characterization of the Delta9 desaturase (Delta9I) gene of a fungus, Mortierella alpina 1S-4, was previously reported. In this study, two genes encoding Delta9 desaturase homologs were isolated from this fungus. One is a Delta9 desaturase (Delta9II) that exhibits 86% amino acid sequence similarity to Delta9I. Functional analysis involving expression of the encoding gene in Aspergillus oryzae revealed that Delta9II exhibits Delta9 desaturase activity, 18:0 being converted to 18:1Delta9. However, unlike Delta9I, the Delta9II transformant accumulated a low amount of 16:1Delta9. The other homolog is a omega9 desaturase (omega9) that exhibits 56 and 58% amino acid sequence similarity to Delta9I and Delta9II, respectively. On functional analysis with the Aspergillus transformant, it was found that omega9 does not convert 18:0 to 18:1Delta9, but converts 24:0 and 26:0 to 24:1omega9 and 26:1omega9, respectively. On the other hand, Delta9 desaturation-defective mutants characterized by accumulation of 18:0 were derived from M. alpina 1S-4 with a chemical mutagen, and the mutated sites of the Delta9 desaturase genes were identified. The mutation on the Delta9I gene was assumed to cause an amino acid replacement (W136Stop, G265D, and W360Stop) in the mutants (HR222, T4, and ST56), respectively. In these mutants, there was no mutated site on the Delta9II and omega9 genes. Real-time quantitative PCR (RTQ-PCR) analysis revealed that (1) the transcriptional level of the Delta9I gene in HR222 and T4 was much higher than that in the wild strain until the fifth day of the cultivation periods, (2) the Delta9II gene of the mutants was transcribed until the fourth day at the same level as the Delta9I gene of the wild strain, whereas the Delta9II gene of the wild strain was transcribed at a lower level, and (3) the transcriptional level of the omega9 gene in both the mutants and the wild strain was low, i.e., as low as that of the Delta9II gene of the wild strain. In these Delta9 desaturation-defective mutants, Delta9II is likely to play an important role in Delta9 desaturation.

Cloning and functional characterization of a Delta12 fatty acid desaturase gene from the basidiomycete Lentinula edodes

In the basidiomycete Lentinula edodes, a famous edible mushroom (shiitake), the fatty acyl composition of total lipids has previously been shown to change during cell differentiation. In the present study, we succeeded in cloning a gene for a Delta12 fatty acid desaturase from L. edodes. The ORF of this gene (named Le-FAD2) consists of 1308 bp and codes for 435 amino acids. The deduced Le-FAD2 protein shows 40-45% identity to Delta12 fatty acid desaturases from other fungi, and the three histidine clusters typical of the catalytic domain of such enzymes are conserved. Expression of the Le-FAD2 gene in the budding yeast Saccharomyces cerevisiae indicated that its product was able to synthesize linoleic acid (C18:2). Analysis of Le-FAD2 expression in L. edodes revealed that levels of transcription were higher in fruiting body primordia and in mature fruiting bodies, the two differentiated tissues, than in mycelium, and reduction of the growth temperature from 25 to 18 degrees C had no effect on the level of the Le-FAD2 transcript. Thus, although Le-FAD2 expression is correlated with the alteration in the complement of unsaturated fatty acids (UFAs) observed during fruiting body formation, the gene does not respond to a downshift in temperature to 18 degrees C.

Two Delta9-stearic acid desaturases are required for Aspergillus nidulans growth and development

Unsaturated fatty acids are important constituents of all cell membranes and are required for normal growth. In the filamentous fungus Aspergillus nidulans, unsaturated fatty acids and their derivatives also influence asexual (conidial) and sexual (ascospore) sporulation processes. To investigate the relationship between fatty acid metabolism and fungal development, we disrupted the A. nidulans sdeA and sdeB genes, both encoding Delta9-stearic acid desaturases responsible for the conversion of palmitic acid (16:0) and stearic acid (18:0) to palmitoleic acid (16:1) and oleic acid (18:1). The effects of sdeA deletion on development were profound, such that growth, conidial and ascospore production were all reduced at 22 and 37 degrees C. Total fatty acid content was increased over 3-fold in the DeltasdeA strain, reflected in up-regulation of the expression of the fasA gene encoding the alpha chain of the fatty acid synthase, compared to wild type. Stearic acid accumulated approximately 3-fold compared to wild type in the DeltasdeA strain, while unsaturated fatty acid production was decreased. In contrast, disruption of sdeB reduced fungal growth and conidiation at 22 degrees C, but did not affect these processes at 37 degrees C compared to wild type. Interestingly, ascospore production was increased at 37 degrees C for DeltasdeB compared to wild type. Total fatty acid content was not increased in this strain, although stearic acid accumulated 2-fold compared to wild type, and unsaturated fatty acid production was decreased. Combining the DeltasdeA and DeltasdeB alleles created a synthetic lethal strain requiring the addition of oleic acid to the medium for a modicum of growth. Taken together, our results suggest a role for sdeA in growth and development at all temperatures, while sdeB is involved in growth and development at lower temperatures.