Characterization of the promoter, downstream target genes and recognition DNA sequence of Mhy1, a key filamentation-promoting transcription factor in the dimorphic yeast Yarrowia lipolytica

Research progress on biosynthesis of erythritol and multi-dimensional optimization of production strategies

Erythritol, as a new type of natural sweetener, has been widely used in food, medical, cosmetics, pharmaceutical and other fields due to its unique physical and chemical properties and physiological functions. In recent years, with the continuous development of strategies such as synthetic biology, metabolic engineering, omics-based systems biology and high-throughput screening technology, people's understanding of the erythritol biosynthesis pathway has gradually deepened, and microbial cell factories with independent modification capabilities have been successfully constructed. In this review, the cheap feedstocks for erythritol synthesis are introduced in detail, the environmental factors affecting the synthesis of erythritol and its regulatory mechanism are described, and the tools and strategies of metabolic engineering involved in erythritol synthesis are summarized. In addition, the study of erythritol derivatives is helpful in expanding its application field. Finally, the challenges that hinder the effective production of erythritol are discussed, which lay a foundation for the green, efficient and sustainable production of erythritol in the future and breaking through the bottleneck of production.

The Roles of Gti1/Pac2 Family Proteins in Fungal Growth, Morphogenesis, Stress Response, and Pathogenicity

Gti1/Pac2 is a fungal-specific transcription factor family with a stable and conserved N-terminal domain. Generally, there are two members in this family, named Gti1/Wor1/Rpy1/Mit1/Reg1/Ros1/Sge1 and Pac2, which are involved in fungal growth, development, stress response, spore production, pathogenicity, and so on. The Gti1/Pac2 family proteins share some conserved and distinct functions. For example, in Schizosaccharomyces pombe, Gti1 promotes the initiation of gluconate uptake during glucose starvation, while Pac2 controls the onset of sexual development in a pathway independent of the cAMP cascade. In the last two decades, more attention was focused on the Gti1 and its orthologs because of their significant effect on morphological switching and fungal virulence. By contrast, limited work was published on the functions of Pac2, which is required for stress responses and conidiation, but plays a minor role in fungal virulence. In this review, we present an overview of our current understanding of the Gti1/Pac2 proteins that contribute to fungal development and/or pathogenicity and of the regulation mechanisms during infection related development. Understanding the working networks of the conserved Gti1/Pac2 transcription factors in fungal pathogenicity not only advances our knowledge of the highly elaborate infection process but may also lead to the development of novel strategies for the control of plant disease. [Formula: see text] Copyright © 2024 The Author(s). This is an open access article distributed under the CC BY-NC-ND 4.0 International license.

Inhibition of hyphal formation together with biochar addition promotes erythritol production by Yarrowia lipolytica

This study aimed to investigate the effect of hyphal formation in Yarrowia lipolytica and biochar addition on erythritol production by submerged fermentation. Hyphal formation significantly inhibited erythritol production by Y. lipolytica. Transcriptome analysis suggested that the impaired erythritol synthesis of hyphal cells was associated with the differential expression of genes involved in amino acid metabolism, lipid metabolism, and cell wall stability. Deletion of RAS2 responsible for yeast-to-hypha transition and EYD1 included in erythritol degradation blocked hyphal formation and improved erythritol production. Biochar prepared from corncob, sugarcane bagasse (SB), corn straw, peanut shell, coconut shell, and walnut shell (WS) had a positive effect on erythritol production, of which WS pyrolyzed at 500°C (WSc) performed the best in flask fermentation. In a 3.7 L bioreactor, 220.20 ± 10 g/L erythritol with a productivity of 2.30 ± 0.10 g/L/h was obtained in the presence of 1.4% (w/v) WSc and 0.7% SBc (SB pyrolyzed at 500°C) within 96 h. These results suggest that inhibition of hyphal formation together with biochar addition is an efficient way to promote erythritol production.

'Mother(Nature) knows best' - hijacking nature-designed transcriptional programs for enhancing stress resistance and protein production in Yarrowia lipolytica; presentation of YaliFunTome database

BACKGROUND

In the era of rationally designed synthetic biology, heterologous metabolites production, and other counter-nature engineering of cellular metabolism, we took a step back and recalled that 'Mother(-Nature) knows best'. While still aiming at synthetic, non-natural outcomes of generating an 'over-production phenotype' we dug into the pre-designed transcriptional programs evolved in our host organism-Yarrowia lipolytica, hoping that some of these fine-tuned orchestrated programs could be hijacked and used. Having an interest in the practical outcomes of the research, we targeted industrially-relevant functionalities-stress resistance and enhanced synthesis of proteins, and gauged them over extensive experimental design's completion.

RESULTS

Technically, the problem was addressed by screening a broad library of over 120 Y. lipolytica strains under 72 combinations of variables through a carefully pre-optimized high-throughput cultivation protocol, which enabled actual phenotype development. The abundance of the transcription program elicitors-transcription factors (TFs), was secured by their overexpression, while challenging the strains with the multitude of conditions was inflicted to impact their activation stratus. The data were subjected to mathematical modeling to increase their informativeness. The amount of the gathered data prompted us to present them in the form of a searchable catalog - the YaliFunTome database ( https://sparrow.up.poznan.pl/tsdatabase/ )-to facilitate the withdrawal of biological sense from numerical data. We succeeded in the identification of TFs that act as omni-boosters of protein synthesis, enhance resistance to limited oxygen availability, and improve protein synthesis capacity under inorganic nitrogen provision.

CONCLUSIONS

All potential users are invited to browse YaliFunTome in the search for homologous TFs and the TF-driven phenotypes of interest.

Transcription factors enhancing synthesis of recombinant proteins and resistance to stress in Yarrowia lipolytica

Resistance to environmental stress and synthesis of recombinant proteins (r-Prots) are both complex, strongly interconnected biological traits relying on orchestrated contribution of multiple genes. This, in turn, makes their engineering a challenging task. One of the possible strategies is to modify the operation of transcription factors (TFs) associated with these complex traits. The aim of this study was to examine the potential implications of selected five TFs (HSF1-YALI0E13948g, GZF1-YALI0D20482g, CRF1-YALI0B08206g, SKN7-YALI0D14520g, and YAP-like-YALI0D07744g) in stress resistance and/or r-Prot synthesis in Yarrowia lipolytica. The selected TFs were over-expressed or deleted (OE/KO) in a host strain synthesizing a reporter r-Prot. The strains were subjected to phenotype screening under different environmental conditions (pH, oxygen availability, temperature, and osmolality), and the obtained data processing was assisted by mathematical modeling. The results demonstrated that growth and the r-Prot yields under specific conditions can be significantly increased or decreased due to the TFs' engineering. Environmental factors "awakening" individual TFs were indicated, and their contribution was mathematically described. For example, OE of Yap-like TF was proven to alleviate growth retardation under high pH, while Gzf1 and Hsf1 were shown to serve as universal enhancers of r-Prot production in Y. lipolytica. On the other hand, KO of SKN7 and HSF1 disabled growth under hyperosmotic stress. This research demonstrates the usefulness of the TFs engineering approach in the manipulation of complex traits and evidences newly identified functions of the studied TFs. KEY POINTS: • Function and implication in complex traits of 5 TFs in Y. lipolytica were studied. • Gzf1 and Hsf1 are the universal r-Prots synthesis enhancers in Y. lipolytica. • Yap-like TF's activity is pH-dependent; Skn7 and Hsf1 act in osmostress response.

High-Level Production of Patchoulol in Yarrowia lipolytica via Systematic Engineering Strategies

Patchoulol is an important sesquiterpene alcohol with a strong and lasting odor, which has led to prominent applications in perfumes and cosmetics. In this study, systematic metabolic engineering strategies were adopted to create an efficient yeast cell factory for patchoulol overproduction. First, a baseline strain was constructed by selecting a highly active patchoulol synthase. Subsequently, the mevalonate precursor pool was expanded to boost patchoulol synthesis. Moreover, a method for downregulating squalene synthesis based on Cu²⁺-repressible promoter was optimized, which significantly improved the patchoulol titer by 100.9% to 124 mg/L. In addition, a protein fusion strategy resulted in a final titer of 235 mg/L in shake flasks. Finally, 2.864 g/L patchoulol could be produced in a 5 L bioreactor, representing a remarkable 1684-fold increase compared to the baseline strain. To our knowledge, this is the highest patchoulol titer reported so far.

Homologous High-Level Lipase and Single-Cell Protein Production with Engineered Yarrowia lipolytica via Scale-Up Fermentation for Industrial Applications

Yarrowia lipolytica is a promising feed additives. Here, we aimed to produce extracellular lipases and single-cell proteins (SCPs) at high levels simultaneously through fed-batch fermentation of engineered Y. lipolytica. The parameters for 500 mL shake flask cultures were optimized with a single factorial design. The resultant activity of lipase reached 880.6 U/mL after 84 h of fermentation, and 32.0 g/L fermentation broth of dry SCP was obtained at 120 h. To attain high SCP and lipase productivity, the high-density fed-batch fermentation of Y. lipolytica was scaled up in 10 L, 30 L, and 100 L fermentors. Using glycerol as the sole carbon source, the lipase activity peaked to 8083.3 U/mL, and the final dry SCP weight was 183.1 g/L at 94.6 h in 10 L fermentors. The extracellular lipase activity and SCP weight reached 11,100.0 U/mL and 173.3 g of dry SCP/L at 136 h in 30 L fermentors, respectively. Following 136 h of fed-batch fermentation, the extracellular lipase activity and dry SCP weight reached 8532.0 U/mL and 170.3 g/L in 100 L fermentors, respectively. A balance between the lipase secretion and growth of Y. lipolytica recombinant strain was achieved, indicating that an efficient fermentation strategy could promote further scale-up for industrial SCP production from engineered Y. lipolytica.

Copper Ion Mediates Yeast-to-Hypha Transition in Yarrowia lipolytica

Copper is an essential element that maintains yeast physiological function at low concentrations, but is toxic in excess. This study reported that Cu(II) significantly promoted the yeast-to-hypha transition of Yarrowia lipolytica in dose-dependent manner. Strikingly, the intracellular Cu(II) accumulation was drastically reduced upon hyphae formation. Moreover, we investigated the effect of Cu(II) on the physiological function of Y. lipolytica during the dimorphic transition and found that cellular viability and thermomyces lanuginosus lipase (TLL) were both influenced by the Cu(II)-induced yeast-to-hypha transition. Overall, hyphal cells survived better than yeast-form cells with copper ions. Furthermore, transcriptional analysis of the Cu(II)-induced Y. lipolytica before and after hyphae formation revealed a transition state between them. The results showed multiple differentially expressed genes (DEGs) were turned over between the yeast-to-transition and the transition-to-hyphae processes. Furthermore, gene set enrichment analysis (GSEA) identified that multiple KEGG pathways, including signaling, ion transport, carbon and lipid metabolism, ribosomal, and other biological processes, were highly involved in the dimorphic transition. Importantly, overexpression screening of more than thirty DEGs further found four novel genes, which are encoded by YALI1_B07500g, YALI1_C12900g, YALI1_E04033g, and YALI1_F29317g, were essential regulators in Cu-induced dimorphic transition. Overexpression of each of them will turn on the yeast-to-hypha transition without Cu(II) induction. Taken together, these results provide new insight to explore further the regulatory mechanism of dimorphic transition in Y. lipolytica.

Roles of the transcriptional regulators Fts1, YlNrg1, YlTup1, and YlSsn6 in the repression of the yeast-to-filament transition in the dimorphic yeast Yarrowia lipolytica

In dimorphic fungi, the yeast-to-filament transition critical for cell survival under nutrient starvation is controlled by both activators and repressors. However, very few filamentation repressors are known. Here we report that, in the dimorphic yeast Yarrowia lipolytica, the conserved transcription factor YlNrg1 plays a minor role whereas Fts1, a newly identified Zn(II)₂ Cys₆ zinc cluster transcription factor, plays a key role in filamentation repression. FTS1 deletion caused hyperfilamentation whereas Fts1 overexpression drastically reduced filamentation. The expression of FTS1 is downregulated substantially during the yeast-to-filament transition. Transcriptome sequencing revealed that Fts1 represses 401 genes, including the filamentation-activating transcription factor genes MHY1, YlAZF1, and YlWOR4 and key cell wall protein genes. Tup1-Ssn6, a general transcriptional corepressor, is involved in the repression of many cellular functions in fungi. We show that both YlTup1 and YlSsn6 strongly repress filamentation in Y. lipolytica. YlTup1 and YlSsn6 together repress 1383 genes, including a large number of transcription factor and cell wall protein genes, which overlap substantially with Fts1-repressed genes. Fts1 interacts with both YlTup1 and YlSsn6, and LexA-Fts1 fusion represses a lexAop-promoter-lacZ reporter in a Tup1-Ssn6-dependent manner. Our findings suggest that Fts1 functions as a transcriptional repressor, directing the repression of target genes through the Tup1-Ssn6 corepressor.

The Zinc Finger Transcription Factor Fts2 Represses the Yeast-to-Filament Transition in the Dimorphic Yeast Yarrowia lipolytica

The yeast-to-filament transition is an important cellular response to environmental stimulations in dimorphic fungi. In addition to activators, there are repressors in the cells to prevent filament formation, which is important to keep the cells in the yeast form when filamentation is not necessary. However, very few repressors of filamentation are known so far. Here, we identify a novel repressor of filamentation in the dimorphic yeast Yarrowia lipolytica, Fts2, which is a C₂H₂-type zinc finger transcription factor. We show that fts2Δ cells exhibited increased filamentation under mild filament-inducing conditions and formed filaments under non-filament-inducing conditions. We also show that Fts2 interacts with YlSsn6, component of the Tup1-Ssn6 transcriptional corepressor, and Fts2-LexA represses a lexAop-P_YlACT1-lacZ reporter in a Tup1-Ssn6-dependent manner, suggesting that Fts2 has transcriptional repressor activity and represses gene expression via Tup1-Ssn6. In addition, we show that Fts2 represses a large number of cell wall protein genes and transcription factor genes, some of which are implicated in the filamentation response. Interestingly, about two-thirds of Fts2-repressed genes are also repressed by Tup1-Ssn6, suggesting that Fts2 may repress the bulk of its target genes via Tup1-Ssn6. Lastly, we show that Fts2 expression is downregulated in response to alkaline pH and the relief of negative control by Fts2 facilitates the induction of filamentation by alkaline pH. IMPORTANCE The repressors of filamentation are important negative regulators of the yeast-to-filament transition. However, except in Candida albicans, very few repressors of filamentation are known in dimorphic fungi. More importantly, how they repress filamentation is often not clear. In this paper, we report a novel repressor of filamentation in Y. lipolytica. Fts2 is not closely related in amino acid sequence to CaNrg1 and Rfg1, two major repressors of filamentation in C. albicans, yet it represses gene expression via the transcriptional corepressor Tup1-Ssn6, similar to CaNrg1 and Rfg1. Using transcriptome sequencing, we determined the whole set of genes regulated by Fts2 and identified the major targets of Fts2 repression, which provide clues to the mechanism by which Fts2 represses filamentation. Our results have important implications for understanding the negative control of the yeast-to-filament transition in dimorphic fungi.

"Fight-flight-or-freeze" - how Yarrowia lipolytica responds to stress at molecular level?

Abstract

Yarrowia lipolytica is a popular yeast species employed in multiple biotechnological production processes. High resistance to extreme environmental conditions or metabolic burden triggered by synthetically forced over-synthesis of a target metabolite has its practical consequences. The proud status of an “industrial workhorse” that Y. lipolytica has gained is directly related to such a quality of this species. With the increasing amount of knowledge coming from detailed functional studies and comprehensive omics analyses, it is now possible to start painting the landscape of the molecular background behind stress response and adaptation in Y. lipolytica. This review summarizes the current state-of-art of a global effort in revealing how Y. lipolytica responds to both environmental threats and the intrinsic burden caused by the overproduction of recombinant secretory proteins at the molecular level. Detailed lists of genes, proteins, molecules, and biological processes deregulated upon exposure to external stress factors or affected by over-synthesis of heterologous proteins are provided. Specificities and universalities of Y. lipolytica cellular response to different extrinsic and intrinsic threats are highlighted.

Key points

• Y. lipolytica as an industrial workhorse is subjected to multiple stress factors.

• Cellular responses together with involved genes, proteins, and molecules are reviewed.

• Native stress response mechanisms are studied and inspire engineering strategies.

Morphological and Metabolic Engineering of Yarrowia lipolytica to Increase β-Carotene Production

The oleaginous yeast Yarrowia lipolytica represents an environmentally friendly platform cell factory for β-carotene production. However, Y. lipolytica is a dimorphic species that can undergo a yeast-to-mycelium transition when exposed to stress. The mycelial form is unfavorable for industrial fermentation. In this study, β-carotene-producing Y. lipolytica strains were constructed via the integration of multiple copies of 13 genes related to the β-carotene biosynthesis pathway. The β-carotene content increased by 11.7-fold compared with the start strain T1. As the β-carotene content increased, the oval-shaped yeast form was gradually replaced by hyphae, implying that the accumulation of β-carotene in Y. lipolytica induces a morphological transition. To relieve this metabolic stress, the strains were morphologically engineered by deleting CLA4 and MHY1 genes to convert the mycelium back to the yeast form, which further increased the β-carotene production by 139%. In fed-batch fermentation, the engineered strain produced 7.6 g/L and 159 mg/g DCW β-carotene, which is the highest titer and content reported to date. The morphological engineering strategy developed here may be useful for enhancing chemical synthesis in dimorphic yeasts.

Yarrowia lipolytica as a biorefinery platform for effluents and solid wastes valorization - challenges and opportunities

Due to its physiological and enzymatic features, Yarrowia lipolytica produces several valuable compounds from a wide range of substrates. Appointed by some authors as an industrial workhorse, Y. lipolytica has an extraordinary ability to use unrefined and complex low-cost substrates as carbon and nitrogen sources, aiding to reduce the waste surplus and to produce added-value compounds in a cost-effective way. Dozens of review papers regarding Y. lipolytica have been published till now, proving the interest that this yeast arouses in the scientific community. However, most of them are focused on metabolic pathways involved in substrates assimilation and product formation, or the development of synthetic biology tools in order to obtain engineered strains for biotechnological applications. This paper provides an exhaustive and up-to-date revision on the application of Y. lipolytica to valorize liquid effluents and solid wastes and its role in developing cleaner biotechnological approaches, aiming to boost the circular economy. Firstly, a general overview about Y. lipolytica is introduced, describing its intrinsic features and biotechnological applications. Then, an extensive survey of the literature regarding the assimilation of oily wastes (waste cooking oils, oil cakes and olive mill wastewaters), animal fat wastes, hydrocarbons-rich effluents, crude glycerol and agro-food wastes by Y. lipolytica strains will be discussed. This is the first article that brings together the environmental issue of all such residues and their valorization as feedstock for valuable compounds production by Y. lipolytica. Finally, it will demonstrate the potential of this non-conventional yeast to be used as a biorefinery platform.

The pH-Responsive Transcription Factors YlRim101 and Mhy1 Regulate Alkaline pH-Induced Filamentation in the Dimorphic Yeast Yarrowia lipolytica

Environmental pH influences cell growth and differentiation. In the dimorphic yeast Yarrowia lipolytica, neutral-alkaline pH strongly induces the yeast-to-filament transition. However, the regulatory mechanism that governs alkaline pH-induced filamentation has been unclear. Here, we show that the pH-responsive transcription factor Y. lipolytica Rim101 (YlRim101) is a major regulator of alkaline-induced filamentation, since the deletion of YlRIM101 severely impaired filamentation at alkaline pH, whereas the constitutively active YlRIM101^1-330 mutant mildly induced filamentation at acidic pH. YlRim101 controls the expression of the majority of alkaline-regulated cell wall protein genes. One of these, the cell surface glycosidase gene YlPHR1, plays a critical role in growth, cell wall function, and filamentation at alkaline pH. This finding suggests that YlRim101 promotes filamentation at alkaline pH via controlling the expression of these genes. We also show that, in addition to YlRim101, the Msn2/Msn4-like transcription factor Mhy1 is highly upregulated at alkaline pH and is essential for filamentation. However, unlike YlRim101, which specifically regulates alkaline-induced filamentation, Mhy1 regulates both alkaline- and glucose-induced filamentation, since the deletion of MHY1 abolished them both, whereas the overexpression of MHY1 induced strong filamentation irrespective of the pH or the presence of glucose. Finally, we show that YlRim101 and Mhy1 positively coregulate seven cell wall protein genes at alkaline pH, including YlPHR1 and five cell surface adhesin-like genes, three of which appear to promote filamentation. Together, these results reveal a conserved role of YlRim101 and a novel role of Mhy1 in the regulation of alkaline-induced filamentation in Y. lipolytica IMPORTANCE The regulatory mechanism that governs pH-regulated filamentation is not clear in dimorphic fungi except in Candida albicans Here, we investigated the regulation of alkaline pH-induced filamentation in Yarrowia lipolytica, a dimorphic yeast distantly related to C. albicans Our results show that the transcription factor YlRim101 and the Msn2/Msn4-like transcription factor Mhy1 are the major regulators that promote filamentation at alkaline pH. They control the expression of a number of cell wall protein genes important for cell wall organization and filamentation. Our results suggest that the Rim101/PacC homologs play a conserved role in pH-regulated filamentation in dimorphic fungi.

Yarrowia lipolytica: a multitalented yeast species of ecological significance

Yarrowia lipolytica is characterized by GRAS (Generally regarded as safe) status, the versatile substrate utilization profile, rapid utilization rates, metabolic diversity and flexibility, the unique abilities to tolerate to extreme environments (acidic, alkaline, hypersaline, heavy metal-pollutions and others) and elevated biosynthesis and secreting capacities. These advantages of Y. lipolytica allow us to consider it as having great ecological significance. Unfortunately, there is still a paucity of relevant review data. This mini-review highlights ecological ubiquity of Y. lipolytica species, their ability to diversify and colonize specialized niches. Different Y. lipolytica strains, native and engineered, are beneficial in degrading many environmental pollutants causing serious ecological problems worldwide. In agriculture has a potential to be a bio-control agent by stimulating plant defense response, and an eco-friendly bio-fertilizer. Engineered strains of Y. lipolytica have become a very promising platform for eco-friendly production of biofuel, commodities, chemicals and secondary metabolites of plant origin, obtaining which by other method were limited or economically infeasible, or were accompanied by stringent environmental problems. Perspectives to use potential of Y. lipolytica's capacities for industrial scale production of valuable compounds in an eco-friendly manner are proposed.

Deletion of MHY1 abolishes hyphae formation in Yarrowia lipolytica without negative effects on stress tolerance

There is a need for development of sustainable production processes for production of fats/oils and lipid derived chemicals. The dimorphic oleaginous yeast Yarrowia lipolytica is a promising organism for conversion of biomass hydrolysate to lipids, but in many such processes hyphae formation will be problematic. We have therefore constructed and compared the performance of strains carrying deletions in several published gene targets suggested to abolish hyphae formation (MHY1, HOY1 and CLA4). The MHY1-deletion was the only of the tested strains which did not exhibit hyphae formation under any of the conditions tested. The MHY1-deletion also had a weak positive effect on lipid accumulation without affecting the total fatty acid composition, irrespective of the nitrogen source used. MHY1 has been suggested to constitute a functional homolog of the stress responsive transcription factors MSN2/4 in Saccharomyces cerevisiae, the deletion of which are highly stress sensitive. However, the deletion of MHY1 displayed only minor difference on survival of a range of acute or long term stress and starvation conditions. We conclude that the deletion of MHY1 in Y.lipolytica is a reliable way of abolishing hyphae formation with few detectable negative side effects regarding growth, stress tolerance and lipid accumulation and composition.