Tocopherol and phylloquinone biosynthesis in chloroplasts requires the phytol kinase VITAMIN E PATHWAY GENE5 (VTE5) and the farnesol kinase (FOLK).

Chlorophyll degradation causes the release of phytol, which is converted into phytyl diphosphate (phytyl-PP) by phytol kinase (VITAMIN E PATHWAY GENE5 [VTE5]) and phytyl phosphate (phytyl-P) kinase (VTE6). The kinase pathway is important for tocopherol synthesis, as the Arabidopsis (Arabidopsis thaliana) vte5 mutant contains reduced levels of tocopherol. Arabidopsis harbors one paralog of VTE5, farnesol kinase (FOLK) involved in farnesol phosphorylation. Here, we demonstrate that VTE5 and FOLK harbor kinase activities for phytol, geranylgeraniol, and farnesol with different specificities. While the tocopherol content of the folk mutant is unchanged, vte5-2 folk plants completely lack tocopherol. Tocopherol deficiency in vte5-2 plants can be complemented by overexpression of FOLK, indicating that FOLK is an authentic gene of tocopherol synthesis. The vte5-2 folk plants contain only ∼40% of wild-type amounts of phylloquinone, demonstrating that VTE5 and FOLK both contribute in part to phylloquinone synthesis. Tocotrienol and menaquinone-4 were produced in vte5-2 folk plants after supplementation with homogentisate or 1,4-dihydroxy-2-naphthoic acid, respectively, indicating that their synthesis is independent of the VTE5/FOLK pathway. These results show that phytyl moieties for tocopherol synthesis are completely but, for phylloquinone production, only partially derived from geranylgeranyl-chlorophyll and phytol phosphorylation by VTE5 and FOLK.

Absence of farnesol salvage in Candida albicans and probably in other fungi.

Farnesol salvage, a two-step pathway converting farnesol to farnesyl pyrophosphate (FPP), occurs in bacteria, plants, and animals. This paper investigates the presence of this pathway in fungi. Through bioinformatics, biochemistry, and physiological analyses, we demonstrate its absence in the yeasts Saccharomyces cerevisiae and Candida albicans, suggesting a likely absence across fungi. We screened 1,053 fungal genomes, including 34 from C. albicans, for potential homologs to four genes (Arabidopsis thaliana AtFOLK, AtVTE5, AtVTE6, and Plasmodium falciparum PfPOLK) known to accomplish farnesol/prenol salvage in other organisms. Additionally, we showed that 3H-farnesol was not converted to FPP or any other phosphorylated prenol, and exogenous farnesol was not metabolized within 90 minutes at any phase of growth and did not rescue cells from the toxic effects of atorvastatin, but it did elevate the levels of intracellular farnesol (Fi). All these experiments were conducted with C. albicans. In sum, we found no evidence for farnesol salvage in fungi. IMPORTANCE: The absence of farnesol salvage constitutes a major difference in the metabolic capabilities of fungi. In terms of fungal physiology, the lack of farnesol salvage pathways relates to how farnesol acts as a quorum-sensing molecule in Candida albicans and why farnesol should be investigated for use in combination with other known antifungal antibiotics. Its absence is essential for a model (K. W. Nickerson et al., Microbiol Mol Biol Rev 88:e00081-22, 2024), wherein protein farnesylation, protein chaperones, and the unfolded protein response are combined under the unifying umbrella of a cell's intracellular farnesol (Fi). In terms of human health, farnesol should have at least two different modes of action depending on whether those cells have farnesol salvage. Because animals have farnesol salvage, we can now see the importance of dietary prenols as well as the potential importance of farnesol in treating neurodegenerative diseases such as Parkinson's disease, Alzheimer's disease, and multiple sclerosis.

An inducible potato (E,E)-farnesol synthase confers tolerance against bacterial pathogens in potato and tobacco.

Terpene synthases (TPSs) have diverse biological functions in plants. Though the roles of TPSs in herbivore defense are well established in many plant species, their role in bacterial defense has been scarce and is emerging. Through functional genomics, here we report the in planta role of potato (Solanum tuberosum) terpene synthase (StTPS18) in bacterial defense. Expression of StTPS18 was highest in leaves and was induced in response to Pseudomonas syringae and methyl jasmonate treatments. The recombinant StTPS18 exhibited bona fide (E,E)-farnesol synthase activity forming a sesquiterpenoid, (E,E)-farnesol as the sole product, utilising (E,E)-farnesyl diphosphate (FPP). Subcellular localization of GFP fusion protein revealed that StTPS18 is localized to the cytosol. Silencing and overexpression of StTPS18 in potato resulted in reduced and enhanced tolerance, respectively, to bacterial pathogens P. syringae and Ralstonia solanacearum. Bacterial growth assay using medium containing (E,E)-farnesol significantly inhibited P. syringae growth. Moreover, StTPS18 overexpressing transgenic potato and Nicotiana tabacum leaves, and (E,E)-farnesol and P. syringae infiltrated potato leaves exhibited elevated expression of sterol pathway and members of pathogenesis-related genes with enhanced phytosterol accumulation. Interestingly, enhanced phytosterols in 13 C3 -(E,E)-farnesol infiltrated potato leaves were devoid of any noticeable 13 C labeling, indicating no direct utilization of (E,E)-farnesol in phytosterols formation. Furthermore, leaves of StTPS18 overexpressing transgenic lines had no detectable (E,E)-farnesol similar to the control plant, and emitted lower levels of sesquiterpenes than the control. These findings point towards an indirect involvement of StTPS18 and its product (E,E)-farnesol in bacterial defense through upregulation of phytosterol biosynthesis and defense genes.

Isolation, purification and biochemical characterization of Conopomorpha cramerella farnesol dehydrogenase.

In Southeast Asia, Conopomorpha cramerella (Snellen) which is commonly known as the cocoa pod borer (CPB) moth has been identified as the most detrimental pest of Theobroma cacao L. Apart from the various side effects on human health and non-target organisms, heavily relying on synthetic pyrethroid insecticides to control CPB infestations also increases the environmental contamination risks. Thus, developing biorational insecticides that minimally affect the non-target organism and environment by targeting the insect growth regulation process is needed to manage the pest population. In insects, juvenile hormones (JH) regulate critical biological events, especially metamorphosis, development and reproduction. Since the physiological roles of JH III vary among different organisms, the biochemical properties, especially substrate specificity and analogue inhibition, may also be different. Therefore, studies on the JH III biosynthetic pathway enzymes in both plants and insects are beneficial to discover more effective analogues. Bioinformatic analysis and biochemical characterization of a NADP+ -dependent farnesol dehydrogenase, an intermediate enzyme of the JH III pathway, from C. cramerella (CcFolDH), were described in this study. In addition, the farnesol analogues that may act as a potent analogue inhibitor for CcFolDH ware determined using in vitro enzymatic study. The phylogenetic analysis indicated that CcFolDH shared a close phylogenetic relationship to the honeybee's short-chain dehydrogenase/reductase. The 27 kDa CcFolDH has an NADP(H) binding domain with a typical Rossmann fold and is likely a homotetrameric protein in the solution. The enzyme had a greater preference for substrate trans, trans-farnesol and coenzyme NADP+ . In terms of analogue inhibitor inhibition, hexahydroxyfarnesyl acetone showed the highest inhibition (the lowest Ki ) compared to other farnesol analogues. Thus, hexahydroxyfarnesyl acetone would serve as the most potent active ingredient for future biorational pesticide management for C. cramerella infestation. Based on the bioinformatic analyses and biochemical characterizations conducted in this research, we proposed that rCcFolDH differs slightly from other reported farnesol dehydrogenases in terms of molecular weight, substrate preference, coenzymes utilization and analogue inhibitors selection.

Concurrent administration of farnesol protects acetaminophen-induced acute hepatic necrosis in mice.

Acetaminophen (APAP) is known to cause acute liver injury and acute liver failure in Western countries. This study investigates the protective role of farnesol (FAR) (C15 H26 O), a natural sesquiterpene alcohol in essential oils, against APAP-induced acute liver necrosis in mice. Mice were injected with a single dose of APAP (300 mg/kg) via an intraperitoneal route. Different groups of mice were concurrently treated with a single dose of FAR 25 mg/kg, FAR 50 mg/kg, and N-acetylcysteine. APAP administration caused a significant increase in transaminase activities and malondialdehyde (MDA) levels in the serum and liver tissue, respectively, with a concomitant decrease in intracellular antioxidants, including reduced glutathione (GSH) in the liver tissue. APAP intoxication upregulated proinflammatory cytokines such as tumor necrosis factor-α, interleukin-1ß (IL-1ß), IL-6, nuclear factor-κB (NF-κB), and IκB kinase ß in the liver tissue. FAR and N-acetylcysteine (NAC) administrations concurrently with APAP prevented serum transaminase increase in serum and MDA levels in the liver tissue. A high dose of FAR and NAC treatments significantly inhibited GSH and other antioxidant depletion. FAR and NAC treatments also downregulated the expression of proinflammatory markers. FAR treatments protects against APAP-induced acute liver injury and offers antioxidant and anti-inflammatory effects by inhibiting the NF-κB pathway involved in the transcription of genes responsible for inflammatory cytokine synthesis.

Effect of quorum quenchers on virulence factors production and quorum sensing signalling pathway of non-mucoid, mucoid, and heavily mucoid Pseudomonas aeruginosa.

Quorum quenching (QQ), a mechanism which inhibits, interferes or inactivates quorum sensing, has been investigated for control of biofilms instigated by quorum sensing process. Application of quorum quenchers (QQs) provides the possibility to investigate how different phenotypes of Pseudomonas aeruginosa (non-mucoid, mucoid, and heavily mucoid strains) modulate their gene expression to form biofilms, their quorum sensing (QS) mediated biofilm to be formed, and their virulence expressed. The mRNA expression of the AHL-mediated QS circuit and AHL-mediated virulence factors in P. aeruginosa was investigated in presence of QQs. qPCR analysis showed that farnesol and tyrosol actively reduce the expression of the synthase protein, LasI and RhlI, and prevent production of 3OC12-HSL and C4-HSL, respectively. Also, the use of farnesol and tyrosol significantly moderated gene expression for exo-proteins toxA, aprA, LasB, as well as rhlAB, which are responsible for rhamnolipid production. Our findings were promising, identifying several suppressive regulatory effects of furanone and Candida albicans QS signal molecules, tyrosol, and farnesol on the AHL-mediated P. aeruginosa QS network and related virulence factors.

Functional diversification in the Nudix hydrolase gene family drives sesquiterpene biosynthesis in Rosa × wichurana.

Roses use a non-canonical pathway involving a Nudix hydrolase, RhNUDX1, to synthesize their monoterpenes, especially geraniol. Here we report the characterization of another expressed NUDX1 gene from the rose cultivar Rosa x wichurana, RwNUDX1-2. In order to study the function of the RwNUDX1-2 protein, we analyzed the volatile profiles of an F1 progeny generated by crossing R. chinensis cv. 'Old Blush' with R. x wichurana. A correlation test of the volatilomes with gene expression data revealed that RwNUDX1-2 is involved in the biosynthesis of a group of sesquiterpenoids, especially E,E-farnesol, in addition to other sesquiterpenes. In vitro enzyme assays and heterologous in planta functional characterization of the RwNUDX1-2 gene corroborated this result. A quantitative trait locus (QTL) analysis was performed using the data of E,E-farnesol contents in the progeny and a genetic map was constructed based on gene markers. The RwNUDX1-2 gene co-localized with the QTL for E,E-farnesol content, thereby confirming its function in sesquiterpenoid biosynthesis in R. x wichurana. Finally, in order to understand the structural bases for the substrate specificity of rose NUDX proteins, the RhNUDX1 protein was crystallized, and its structure was refined to 1.7 Å. By molecular modeling of different rose NUDX1 protein complexes with their respective substrates, a structural basis for substrate discrimination by rose NUDX1 proteins is proposed.

Negative Regulation of Human Hepatic Constitutive Androstane Receptor by Cholesterol Synthesis Inhibition: Role of Sterol Regulatory Element Binding Proteins.

The squalene synthase inhibitor squalestatin 1 (Squal1) is a potent and efficacious inducer of CYP2B expression in primary cultured rat hepatocytes and rat liver. To determine whether Squal1 is also an inducer of human CYP2B, the effects of Squal1 treatment were evaluated in primary cultured human hepatocytes, differentiated HepaRG cells, and humanized mouse livers. Squal1 treatment did not increase CYP2B6 mRNA levels in human hepatocytes or HepaRG cells and only slightly and inconsistently increased CYP2B6 mRNA content in humanized mouse liver. However, treatment with farnesol, which mediates Squal1's effect on rat CYP2B expression, increased CYP2B6 mRNA levels in HepaRG cells expressing the constitutive androstane receptor (CAR), but not in cells with knocked-down CAR. To determine the impact of cholesterol biosynthesis inhibition on CAR activation, the effects of pravastatin (Prava) were determined on CITCO-mediated gene expression in primary cultured human hepatocytes. Prava treatment abolished CITCO-inducible CYP2B6 expression, but had less effect on rifampicin-mediated CYP3A4 induction, and CITCO treatment did not affect Prava-inducible HMG-CoA reductase (HMGCR) expression. Treatment with inhibitors of different steps of cholesterol biosynthesis attenuated CITCO-mediated CYP2B6 induction in HepaRG cells, and Prava treatment increased HMGCR expression and inhibited CYP2B6 induction with comparable potency. Transfection of HepG2 cells with transcriptionally active sterol regulatory element binding proteins (SREBPs) reduced CAR-mediated transactivation, and inducible expression of transcriptionally active SREBP2 attenuated CITCO-inducible CYP2B6 expression in HepaRG cells. These findings suggest that Squal1 does not induce CYP2B6 in human hepatocytes because Squal1's inhibitory effect on cholesterol biosynthesis interferes with CAR activation. SIGNIFICANCE STATEMENT: The cholesterol biosynthesis inhibitor squalestatin 1 induces rat hepatic CYP2B expression indirectly by causing accumulation of an endogenous isoprenoid that activates the constitutive androstane receptor (CAR). This study demonstrates that squalestatin 1 does not similarly induce CYP2B6 expression in human hepatocytes. Rather, inhibition of cholesterol biosynthesis interferes with CAR activity, likely by activating sterol regulatory element binding proteins. These findings increase our understanding of the endogenous processes that modulate human drug-metabolizing gene expression.

Enhancement of NADPH availability for coproduction of coenzyme Q10 and farnesol from Rhodobacter sphaeroides.

Coenzyme Q10 (CoQ10)-an essential cofactor in the respiratory electron transport chain-has important pharmaceutical and healthcare applications. Farnesol (FOH)-an acyclic sesquiterpene alcohol-has garnered interest owing to its valuable clinical and medical benefits. Here, the coproduction of CoQ10 and FOH in Rhodobacter sphaeroides GY-2 was greatly improved through the enhancement of intracellular NADPH availability. Transcription of pgi, gdhA, and nuocd was, respectively, inhibited using RNA interference to reduce intracellular NAD(P)H consumption. Moreover, zwf, gnd, and zwf + gnd were overexpressed to enhance the pentose phosphate pathway, resulting in improved NADPH availability in most metabolically engineered R. sphaeroides strains. RSg-pgi with RNAi of pgi combined with overexpression of gnd produced 55.05 mg/L FOH that is twofold higher than the parental strain GY-2, and 185.5 mg/L CoQ10 can be coproduced at the same time. In conclusion, improved carbon flux can be redirected toward NADPH-dependent biosynthesis through the enhancement of NADPH availability.

The inhibition of trans-cinnamaldehyde on the virulence of Candida albicans via enhancing farnesol secretion with low potential for the development of resistance.

The emergence of drug resistance and limitation of antifungal agents complicate the management of fungal infection. Candida albicans, as the most common fungal infection pathogen, causes candidiasis via developing its virulence factors. In this study, we found trans-cinnamaldehyde (TC), known as a "Generally Regarded As Safe" (GRAS) molecule, had moderate antifungal activities against various Candida species and could retard the virulence of C. albicans in a dose-dependent manner by inhibiting the adhesion, morphological transition and biofilms formation. The mechanisms investigation revealed that the inhibition of hyphae and biofilms development was caused by the increasing farnesol secretion induced by Dpp3 expression. Since drug resistance restricted the treatment of clinical fungal infection, we explored the capacity of TC to develop drug-resistance under a long time TC treatment. Results showed that TC had little chance to form resistance by a serial passage experiment. Our work illustrates the underlying mechanism of TC inhibition of morphological transition and provides a optional application in treating the relevant fungal infections by targeting fungal virulence factors.

RNA sequencing analysis of Cymbidium goeringii identifies floral scent biosynthesis related genes.

BACKGROUND: Cymbidium goeringii belongs to the Orchidaceae, which is one of the most abundant angiosperm families. Cymbidium goeringii consist with high economic value and characteristics include fragrance and multiple flower colors. Floral scent is one of the important strategies for ensuring fertilization. However, limited genetic data is available in this non-model plant, and little known about the molecular mechanism responsible for floral scent in this orchid. Transcriptome and expression profiling data are needed to identify genes and better understand the biological mechanisms of floral scents in this species. Present transcriptomic data provides basic information on the genes and enzymes related to and pathways involved in flower secondary metabolism in this plant. RESULTS: In this study, RNA sequencing analyses were performed to identify changes in gene expression and biological pathways related scent metabolism. Three cDNA libraries were obtained from three developmental floral stages: closed bud, half flowering stage and full flowering stage. Using Illumina technique 159,616,374 clean reads were obtained and were assembled into 85,868 final unigenes (average length 1194 nt), 33.85% of which were annotated in the NCBI non redundant protein database. Among this unigenes 36,082 were assigned to gene ontology and 23,164 were combined with COG groups. Total 33,417 unigenes were assigned in 127 pathways according to the Kyoto Encyclopedia of Genes and Genomes pathway database. According these transcriptomic data we identified number of candidates genes which differentially expressed in different developmental stages of flower related to fragrance biosynthesis. In q-RT-PCR most of the fragrance related genes highly expressed in half flowering stage. CONCLUSIONS: RNA-seq and DEG data provided comprehensive gene expression information at the transcriptional level that could be facilitate the molecular mechanisms of floral biosynthesis pathways in three developmental phase's flowers in Cymbidium goeringii, moreover providing useful information for further analysis on C. goeringii, and other plants of genus Cymbidium.

Co-production of farnesol and coenzyme Q10 from metabolically engineered Rhodobacter sphaeroides.

BACKGROUND: Farnesol is an acyclic sesquiterpene alcohol present in the essential oils of various plants in nature. It has been reported to be valuable in medical applications, such as alleviation of allergic asthma, gliosis, and edema as well as anti-cancerous and anti-inflammatory effects. Coenzyme Q10 (CoQ10), an essential cofactor in the aerobic respiratory electron transport chain, has attracted growing interest owing to its clinical benefits and important applications in the pharmaceutical, food, and health industries. In this work, co-production of (E,E)-farnesol (FOH) and CoQ10 was achieved by combining 3 different exogenous terpenes or sesquiterpene synthase with the RNA interference of psy (responsible for phytoene synthesis in Rhodobacter sphaeroides GY-2). RESULTS: FOH production was significantly increased by overexpressing exogenous terpene synthase (TPS), phosphatidylglycerophosphatase B (PgpB), and sesquiterpene synthase (ATPS), as well as RNAi-mediated silencing of psy coding phytoene synthase (PSY) in R. sphaeroides strains. Rs-TPS, Rs-ATPS, and Rs-PgpB respectively produced 68.2%, 43.4%, and 21.9% higher FOH titers than that of the control strain. Interestingly, the CoQ10 production of these 3 recombinant R. sphaeroides strains was exactly opposite to that of FOH. However, CoQ10 production was almost unaffected in R. sphaeroides strains modified by psy RNA interference. The highest FOH production of 40.45 mg/L, which was twice as high as that of the control, was obtained from the TPS-PSYi strain, where the exogenous TPS was combined with the weakening of the phytoene synthesis pathway via psy RNA interference. CoQ10 production in TPS-PSYi, ATPS-PSYi, and PgpB-PSYi was decreased and lower than that of the control strain. CONCLUSIONS: The original flux that contributed to phytoene synthesis was effectively redirected to provide precursors toward FOH or CoQ10 synthesis via psy RNA interference, which led to weakened carotenoid synthesis. The improved flux that was originally involved in CoQ10 production and phytoene synthesis was redirected toward FOH synthesis via metabolic modification. This is the first reported instance of FOH and CoQ10 co-production in R. sphaeroides using a metabolic engineering strategy.

Efficient production of lycopene in Saccharomyces cerevisiae by enzyme engineering and increasing membrane flexibility and NAPDH production.

Lycopene is a red carotenoid pigment with strong antioxidant activity. Saccharomyces cerevisiae is considered a promising host to produce lycopene, but lycopene toxicity is one of the limiting factors for high-level production. In this study, we used heterologous lycopene biosynthesis genes crtE and crtI from Xanthophyllomyces dendrorhous and crtB from Pantoea agglomerans for lycopene production in S. cerevisiae. The crtE, crtB, and crtI genes were integrated into the genome of S. cerevisiae CEN.PK2-1C strain, while deleting DPP1 and LPP1 genes to inhibit a competing pathway producing farnesol. Lycopene production was further improved by inhibiting ergosterol production via downregulation of ERG9 expression and by deleting ROX1 or MOT3 genes encoding transcriptional repressors for mevalonate and sterol biosynthetic pathways. To further increase lycopene production, CrtE and CrtB mutants with improved activities were isolated by directed evolution, and subsequently, the mutated genes were randomly integrated into the engineered lycopene-producing strains via delta-integration. To relieve lycopene toxicity by increasing unsaturated fatty acid content in cell membranes, the OLE1 gene encoding stearoyl-CoA 9-desaturase was overexpressed. In combination with the overexpression of STB5 gene encoding a transcription factor involved in NADPH production, the final strain produced up to 41.8 mg/gDCW of lycopene, which is approximately 74.6-fold higher than that produced in the initial strain.

Deciphering fungal dimorphism: Farnesol's unanswered questions.

Candida albicans excretes E,E-farnesol as a virulence factor and quorum sensing molecule that prevents the yeast to hyphal conversion. Polke et al. (2016) identified eed1Δ/Δ as the first farnesol hypersensitive mutant of C. albicans. eed1Δ/Δ also excretes 10X more farnesol and while able to form hyphae, it cannot maintain hyphae. This mutant enables new research into unanswered questions, including the existence of potential farnesol receptors and transporters, regulation of farnesol synthesis, and relationships among farnesol, germ tube formation and hyphal maintenance. The eed1 farnesol hypersensitivity can be explained by higher internal concentrations of farnesol or lower thresholds for response. One possibility invokes misexpression of a transporter. Saccharomyces cerevisiae and C. albicans have transporters for farnesylated peptides, like the a-factor pheromone, which could potentially also transport farnesol for virulence and quorum sensing. Significantly, these transporters are repressed in MTLa/MTLα C. albicans. An evolutionary pressure for C. albicans to become diploid could derive from its use of farnesol. Alternatively, maintenance of hyphal growth may increase the farnesol response threshold. Finally, Dpp1p, Dpp2p and Dpp3p are non-specific pyrophosphatases responsible for farnesol synthesis. Changes in expression of these enzymes do not explain differences in farnesol levels implicating involvement of additional factors like a scaffolding molecule.

A functional link between hyphal maintenance and quorum sensing in Candida albicans.

Morphogenesis in Candida albicans requires hyphal initiation and maintenance, and both processes are regulated by the fungal quorum sensing molecule (QSM) farnesol. We show that deletion of C. albicans EED1, which is crucial for hyphal extension and maintenance, led to a dramatically increased sensitivity to farnesol, and thus identified the first mutant hypersensitive to farnesol. Furthermore, farnesol decreased the transient filamentation of an eed1Δ strain without inducing cell death, indicating that two separate mechanisms mediate quorum sensing and cell lysis by farnesol. To analyze the cause of farnesol hypersensitivity we constructed either hyperactive or deletion mutants of factors involved in farnesol signaling, by introducing the hyperactive RAS1G13V or pADH1-CYR1CAT allele, or deleting CZF1 or NRG1 respectively. Neither of the constructs nor the exogenous addition of dB-cAMP was able to rescue the farnesol hypersensitivity, highlighting that farnesol mediates its effects not only via the cAMP pathway. Interestingly, the eed1Δ strain also displayed increased farnesol production. When eed1Δ was grown under continuous medium flow conditions, to remove accumulating QSMs from the supernatant, maintenance of eed1Δ filamentation, although not restored, was significantly prolonged, indicating a link between farnesol sensitivity, production, and the hyphal maintenance-defect in the eed1Δ mutant strain.

Influence of phosphatidylserine and phosphatidylethanolamine on farnesol tolerance in Candida albicans.

Candida albicans is among the most common human fungal pathogens. The ability to undergo the morphological transition from yeast to hyphal growth is critical for its pathogenesis. Farnesol, a precursor in the isoprenoid/sterol pathway, is a quorum-sensing molecule produced by C. albicans that inhibits hyphal growth in this polymorphic fungus. Interestingly, C. albicans can tolerate farnesol concentrations that are toxic to other fungi. We hypothesized that changes in phospholipid composition are one of the factors contributing to farnesol tolerance in C. albicans. In this study, we found that loss of enzymes that synthesize the phospholipids phosphatidylserine (PS) and/or phosphatidylethanolamine (PE) compromise the tolerance of C. albicans to farnesol. Compared with wild type, the phospholipid mutant cho1∆/∆ (loss of PS and decreased PE synthesis) shows greater inhibition of growth, loss of ATP production, increased consumption of oxygen, and increased formation of reactive oxygen species in the presence of farnesol. The cho1∆/∆ mutant also exhibits decreased sensitivity to mitochondrial ATPase inhibition, suggesting that cells lacking PS and/or downstream PE rely less on mitochondrial function for ATP synthesis. These data reveal that PS and PE play roles in farnesol tolerance and maintaining mitochondrial respiratory function.

Farnesol signalling in Candida albicans - more than just communication.

Candida albicans is a successful colonizer of the human host, which can, under certain circumstances cause a range of clinically diverse infections. Important virulence-associated traits of the fungus, such as the dimorphic switch and biofilm formation, are controlled by the quorum sensing molecule farnesol. Given the potential of farnesol as a novel antifungal drug, there has been increasing research into the mechanism underlying farnesol sensing and action in C. albicans. However, despite the identification of various factors involved in farnesol signalling, its exact mode of action remains largely unclear. This review provides an overview of the currently known aspects of farnesol production, sensing and action within C. albicans. We also illustrate the characteristic of C. albicans to simultaneously produce and tolerate high farnesol concentrations that are lethal to other microbes. Furthermore, we summarize new literature on the role of farnesol in the interaction of C. albicans with the human host and highlight its action as a potent immunomodulatory molecule.

In Vitro Antibiofilm Activity of Eucarobustol E against Candida albicans.

Formyl-phloroglucinol meroterpenoids (FPMs) are important types of natural products with various bioactivities. Our antifungal susceptibility assay showed that one of the Eucalyptus robusta-derived FPMs, eucarobustol E (EE), exerted a strong inhibitory effect against Candida albicans biofilms at a concentration of 16 µg/ml. EE was found to block the yeast-to-hypha transition and reduce the cellular surface hydrophobicity of the biofilm cells. RNA sequencing and real-time reverse transcription-PCR analysis showed that exposure to 16 µg/ml of EE resulted in marked reductions in the levels of expressions of genes involved in hyphal growth (EFG1, CPH1, TEC1, EED1, UME6, and HGC1) and cell surface protein genes (ALS3, HWP1, and SAP5). Interestingly, in response to EE, genes involved in ergosterol biosynthesis were downregulated, while the farnesol-encoding gene (DPP3) was upregulated, and these findings were in agreement with those from the quantification of ergosterol and farnesol. Combined with the obvious elevation of negative regulator genes (TUP1, NRG1), we speculated that EE's inhibition of carbon flow to ergosterol triggered the mechanisms of the negative regulation of hyphal growth and eventually led to biofilm inhibition.

Quorum sensing by farnesol revisited.

Quorum sensing, a form of molecular communication in microbial communities, is relatively well studied in bacterial species, but poorly understood in fungi. Farnesol, a quorum sensing molecule secreted by the opportunistic human pathogenic fungus Candida albicans, was the first quorum sensing molecule described in a eukaryotic organism. However, despite considerable research efforts and advances in recent years, the mechanisms behind its action remain largely elusive. Only recently, we showed that deletion of the C. albicans gene EED1 (eed1Δ), which is essential for hyphal maintenance, resulted in both increased farnesol production and hypersensitivity to farnesol, providing a link between farnesol signaling and elongated hyphal growth. This finding raised several questions concerning farnesol signaling. In this short review we use the unique phenotype of the eed1Δ mutant to summarize current hypotheses and to speculate on possible mechanisms of quorum sensing in C. albicans and its implication in fungus-host interaction, by drawing comparisons to comparatively well-studied quorum sensing systems in bacteria.

Polymicrobial infections involving clinically relevant Gram-negative bacteria and fungi.

Interactions between fungi and bacteria and their relevance to human health and disease have recently attracted increased attention in biomedical fields. Emerging evidence shows that bacteria and fungi can have synergistic or antagonistic interactions, each with important implications for human colonization and disease. It is now appreciated that some of these interactions may be strategic and helps promote the survival of one or both microorganisms within the host. This review will shed light on clinically relevant interactions between fungi and Gram-negative bacteria. Mechanism of interaction, host immune responses, and preventive measures will also be reviewed.