Transport In Yeast Research Articles

Ceramide sorting into non-vesicular transport is independent of acyl chain length in budding yeast

The transport of ceramide from the endoplasmic reticulum (ER) to the Golgi is a key step in the synthesis of complex sphingolipids, the main building blocks of the plasma membrane. In yeast, ceramide is transported to the Golgi either through ATP-dependent COPII vesicles of the secretory pathway or by ATP-independent non-vesicular transport that involves tethering proteins at ER-Golgi membrane contact sites. Studies in both mammalian and yeast cells reported that vesicular transport mainly carries ceramide containing very long chain fatty acids, while the main mammalian non-vesicular ceramide transport protein CERT only transports ceramides containing short chain fatty acids. However, if non-vesicular ceramide transport in yeast similarly favors short chain ceramides remained unanswered. Here we employed a yeast GhLag1 strain in which the endogenous ceramide synthase is replaced by the cotton-derived GhLag1 gene, resulting in the production of short chain C18 rather than C26 ceramides. We show that block of vesicular transport through ATP-depletion or the use of temperature-sensitive sec mutants caused a reduction in inositolphosphorylceramide (IPC) synthesis to similar extent in WT and GhLag1 backgrounds. Since the remaining IPC synthesis is a readout for non-vesicular ceramide transport, our results indicate that non-vesicular ceramide transport is neither blocked nor facilitated when only short chain ceramides are present. Therefore, we propose that the sorting of ceramide into non-vesicular transport is independent of acyl chain length in budding yeast.

CPK10 protein kinase regulates Arabidopsis tolerance to borondeficiency through phosphorylation and activation of BOR1 transporter.

Boron (B) is crucial for plant growth and development. B deficiency can impair numerous physiological and metabolic processes, particularly in root development and pollen germination, seriously impeding crop growth and yield. However, the molecular mechanism underlying boron signal perception and signal transduction is rather limited. In this study, we discovered that CPK10, a calcium-dependent protein kinase in the CPK family, has the strongest interaction with the boron transporter BOR1. Mutations in CPK10 led to growth and root development defects under B-deficiency conditions, while constitutively active CPK10 enhanced plant tolerance to B deficiency. Furthermore, we found that CPK10 interacted with and phosphorylated BOR1 at the Ser689 residue. Through various biochemical analyses and complementation of B transport in yeast and plants, we revealed that Ser689 of BOR1 is important for its transport activity. In summary, these findings highlight the significance of the CPK10-BOR1 signaling pathway in maintaining B homeostasis in plants and provide targets for the genetic improvement of crop tolerance to B-deficiency stress.

Insights into the role of sterol metabolism in antifungal drug resistance: a mini-review.

Sterols are essential for eukaryotic cells and are crucial in cellular membranes' structure, function, fluidity, permeability, adaptability to environmental stressors, and host-pathogen interactions. Fungal sterol, such as ergosterol metabolism, involves several organelles, including the mitochondria, lipid droplets, endoplasmic reticulum, and peroxisomes that can be regulated mainly by feedback mechanisms and transcriptionally. The majority of sterol transport in yeast occurs via non-vesicular transport pathways mediated by lipid transfer proteins, which determine the quantity of sterol present in the cell membrane. Pathogenic fungi Candida, Aspergillus, and Cryptococcus species can cause a range of superficial to potentially fatal systemic and invasive infections that are more common in immunocompromised patients. There is a significant risk of morbidity and mortality from these infections, which are very difficult to cure. Several antifungal drugs with different modes of action have received clinical approval to treat fungal infections. Antifungal drugs targeting the ergosterol biosynthesis pathway are well-known for their antifungal activity; however, an imbalance in the regulation and transport of ergosterol could lead to resistance to antifungal therapy. This study summarizes how fungal sterol metabolism and regulation can modulate sterol-targeting antifungal drug resistance.

LAMinar Flow: Sterol Transport in a Pathogenic Yeast.

Cryptococcus neoformans is an important fungal pathogen, responsible for over 140,000 deaths per year worldwide. Like other yeasts, C. neoformans relies on ergosterol as its major membrane sterol and carefully regulates its synthesis and distribution. Ergosterol is also targeted by two of the three compound classes currently used to treat cryptococcal infection. We recently reported the discovery and characterization in C. neoformans of a single retrograde ergosterol transporter of the LAM family, Ysp2. Here we review these findings and discuss directions for future research, including the connections between processes that are perturbed by the absence of Ysp2 (which also abrogates cryptococcal virulence) and possible roles for Ysp2 and other, as yet unknown, lipid transport proteins in this organism.

Unlocking the secrets of peptide transport in wine yeast: insights into oligopeptide transporter functions and nitrogen source preferences.

Limited nitrogen supply can prevent the completion of alcoholic fermentation. Supplementation through peptides as an alternative, natural source of nitrogen for yeast offers an interesting solution for this issue. In this work, the S. cerevisiae peptide transporters of the Opt and Fot families were studied. We demonstrated that Fot and Opt2 have a broader peptide length preference than previously reported, enabling yeasts to acquire sufficient nitrogen from peptides without requiring additional ammonia or amino acids to complete fermentation. On the contrary, Opt1 was unable to consume any peptide in the given conditions, whereas it has been described elsewhere as the main peptide transporter for peptides longer than three amino acid residues in experiments in laboratory conditions. This controversy signifies the need in applied sciences for approaching experimental conditions to those prevalent in the industry for its more accurate characterization. Altogether, this work provides further evidence of the importance of peptides as a nitrogen source for yeast and their consequent positive impact on fermentation kinetics.

Calcium-dependent protein kinases CPK21 and CPK23 phosphorylate and activate the iron-regulated transporter IRT1 to regulate iron deficiency in Arabidopsis.

Iron (Fe) is an essential micronutrient for all organisms. Fe availability in the soil is usually much lower than that required for plant growth, and Fe deficiencies seriously restrict crop growth and yield. Calcium (Ca2+) is a second messenger in all eukaryotes; however, it remains largely unknown how Ca2+ regulates Fe deficiency. In this study, mutations in CPK21 and CPK23, which are two highly homologous calcium-dependent protein kinases, conferredimpaired growth and rootdevelopment under Fe-deficient conditions, whereas constitutively active CPK21 and CPK23 enhanced plant tolerance to Fe-deficient conditions. Furthermore, we found that CPK21 and CPK23 interacted with and phosphorylated the Fe transporter IRON-REGULATED TRANSPORTER1 (IRT1) at the Ser149 residue. Biochemical analyses and complementation of Fe transport in yeast and plants indicated that IRT1 Ser149 is critical for IRT1 transport activity. Taken together, these findings suggest that the CPK21/23-IRT1 signaling pathway is critical for Fe homeostasis in plants and provides targets for improving Fe-deficient environments and breeding crops resistant to Fe-deficient conditions.

Adaptive Laboratory Evolution Reveals the Selenium Efflux Process To Improve Selenium Tolerance Mediated by the Membrane Sulfite Pump in Saccharomyces cerevisiae.

Selenium (Se) is a micronutrient in most eukaryotes, and Se-enriched yeast is the most common selenium supplement. However, selenium metabolism and transport in yeast have remained unclear, greatly hindering the application of this element. To explore the latent selenium transport and metabolism mechanisms, we performed adaptive laboratory evolution under the selective pressure of sodium selenite and successfully obtained selenium-tolerant yeast strains. Mutations in the sulfite transporter gene ssu1 and its transcription factor gene fzf1 were found to be responsible for the tolerance generated in the evolved strains, and the selenium efflux process mediated by ssu1 was identified in this study. Moreover, we found that selenite is a competitive substrate for sulfite during the efflux process mediated by ssu1, and the expression of ssu1 is induced by selenite rather than sulfite. Based on the deletion of ssu1, we increased the intracellular selenomethionine content in Se-enriched yeast. This work confirms the existence of the selenium efflux process, and our findings may benefit the optimization of Se-enriched yeast production in the future. IMPORTANCE Selenium is an essential micronutrient for mammals, and its deficiency severely threatens human health. Yeast is the model organism for studying the biological role of selenium, and Se-enriched yeast is the most popular selenium supplement to solve Se deficiency. The cognition of selenium accumulation in yeast always focuses on the reduction process. Little is known about selenium transport, especially selenium efflux, which may play a crucial part in selenium metabolism. The significance of our research is in determining the selenium efflux process in Saccharomyces cerevisiae, which will greatly enhance our knowledge of selenium tolerance and transport, facilitating the production of Se-enriched yeast. Moreover, our research further advances the understanding of the relationship between selenium and sulfur in transport.

Analysis of aquaporins in northern grasses reveal functional importance of Puccinellia nuttalliana PIP2;2 in salt tolerance.

To better understand the roles of aquaporins in salt tolerance, we cloned PIP2;1, PIP2;2, PIP2;3, PIP1;1, PIP1;3, and TIP1;1 aquaporins from three northern grasses varying is salt tolerance including the halophytic grass Puccinellia nuttalliana, moderately salt tolerant Poa juncifolia, and relatively salt sensitive Poa pratensis. We analysed aquaporin expression in roots by exposing the plants to 0 and 150 mM for 6 days in hydroponic culture. NaCl treatment upregulated several PIP transcripts in P. nuttalliana while decreasing PnuTIP1;1. The PnuPIP2;2 transcripts increased by about six-fold in P. nuttalliana, two-fold in Poa juncifolia, and did not change in Poa pratensis. The NaCl treatment enhanced the rate of water transport in yeast expressing PnuPIP2;2 by 56% compared with control. PnuPIP2,2 expression also resulted in a higher Na+ uptake in yeast cells compared with an empty vector suggesting that PnuPIP2;2 may have both water and ion transporting functions. Structural analysis revealed that the transport properties of PnuPIP2;2 could be affected by its unique pore characteristics, which include a combination of hourglass, cylindrical, and increasing diameter conical entrance shape with pore hydropathy of -0.22.

Mathematical and numerical modelling of copper transport in yeast

The transport and regulation of metals in eukaryotic cells is a complex process, dependent on protein transporters that respond to cell needs. The application of dynamic mathematical models can provide valuable insights into these transport mechanisms. Mathematical simulations of transport processes may not directly predict transport mechanisms but can guide experimental design or identify inconsistencies between observation and hypotheses. Copper is an essential metal in eukaryotic cells as a catalytic co-factor in metallochaperone proteins and is therefore tightly regulated in living systems, making it valuable for quantifying biological transport mechanisms. In order to test our modeling system, a culture of baker’s yeast (Saccharomyces cerevisiae) was grown, copper concentrations were obtained from the cells and growth media, and a mathematical model was developed to investigate transport mechanisms between the growth media and the cells. A model based on conservation of mass was presented as a system of equations upon which to develop. This system of equations was developed to include an active transport term that describes a homeostatic concentration that cells actively maintain through negative feedback, and with a delayed activation, the model was more accurate at predicting the experimental data. The hypothesis and dynamic model derived in this work provide a novel framework that may be applied to additional metals or used to describe other transport mechanisms in biological systems.

Testing the Ability of Borate Transporter Orthologs to Complement Saccharomyces cerevisiae BOR1

In S. cerevisiae, borate resistance is mediated by the borate transport protein Bor1p. In plants, the role of borate transport is more complicated given the organism’s need to prevent borate toxicity while maintaining high enough levels of borate as a micronutrient that supports growth. As a result of these complex needs, the borate transporter family has expanded in plants, with seven borate transporters in Arabidopsis thalianaand four borate transporters in Oryza sativa. In humans, the transporter SLC4A11 has been suggested to transport borate, but this claim remains controversial. To better understand the transport activities of purported borate transporters, we tested the ability of eleven plant transporters and one human transporter to complement a BOR1 deletion in S. cerevisiae. We show that AtBor4, AtBor5, Atbor7, and OsBor3, can each complement yeast BOR1, while the other seven plant transporters do not. Interestingly, mapping these results onto phylogenetic analyses revealing two known clades within the borate transporter family might shed light on their functional and evolutionary differences. Next, we tested whether the ability to complement in yeast could be explained by the identity of the protein’s two domains, the Core and the Gate, by creating chimeric constructs combining the Core and Gate domains of AtBor1 and AtBor4. Our data show that neither chimeric construct complements, and thus the ability to complement arises synergistically from elements present in both domains rather than those that lie within just one protein domain. Lastly, we show that human SLC4A11 does not support borate transport in yeast, supporting claims that its transported substrate is not borate.

Structural basis for Rab6 GTPase activation by the Ric1‐Rgp1 complex

Membrane trafficking is a highly coordinated process in eukaryotes essential for maintaining lipid homeostasis and sorting proteins to the proper location inside cells. At the hub of this dynamic set of pathways, the Golgi complex directs much of this sorting through vesicle mediated transport. Vesicles of varying lipid composition loaded with different protein cargo are in constant flux through the Golgi and precise coordination of these processes requires communication between compartments. Rab GTPases are small signaling proteins that act as molecular switches to regulate vesicular trafficking. Rab6 functions at the Golgi and is important for endosome to Golgi retrograde transport in both yeast and metazoans and for anterograde exit from the TGN in metazoans. The Ric1‐Rgp1 protein complex is a highly conserved guanine nucleotide exchange factor (GEF) required for activation of Rab6. In mammalian cells Ric1‐Rgp1 is known to be regulated by the Rab33 GTPase, but it remains unresolved how the activity of the complex is regulated and how it interacts with Rab6. Furthermore, very little is known about the structure and domain organization of Ric1‐Rgp1. We have used cryo‐EM to determine the high‐resolution structure of the yeast Ric1‐Rgp1‐Rab6(Ypt6) complex, representing the key intermediate of the nucleotide exchange reaction. This structure reveals the overall architecture of the complex and has enabled us to identify the specific interactions that govern activation of Rab6. Ongoing studies aim to test the physiological significance of these interactions and determine the orientation of this complex on the Golgi membrane surface.

Transport efficiency of AtGTR1 dependents on the hydrophobicity of transported glucosinolates

Glucosinolates (GLSs) are a group of secondary metabolites that are involved in the defense of herbivores. In Arabidopsis thaliana, Glucosinolate Transporter 1 (AtGTR1) transports GLSs with high affinity via a proton gradient-driven process. In addition to transporting GLSs, AtGTR1 also transports phytohormones, jasmonic acid-isoleucine (JA-Ile), and gibberellin (GA). However, little is known about the mechanisms underlying the broad substrate specificity of AtGTR1. Here, we characterized the substrate preference of AtGTR1 by using a yeast uptake assay, and the results revealed that GLS transport rates are negatively correlated with the hydrophobicity of substrates. Interestingly, the AtGTR1 showed a higher substrate affinity for GLSs with higher hydrophobicity, suggesting a hydrophobic substrate binding pocket. In addition, competition assays revealed that JA, salicylic acid (SA), and indole-3-acetic acid (IAA) competed with GLS for transport in yeast, suggesting a potential interaction of AtGTR1 with these phytohormones. To further characterize the functional properties of AtGTR1, mutagenesis experiments confirmed that the conserved EXXEK motif and Arg166 are essential for the GLS transport function. In addition, the purified AtGTR1 adopts a homodimeric conformation, which is possibly regulated by phosphorylation on Thr105. The phosphomimetic mutation, T105D, reduced its protein expression and completely abrogated its GLS transport function, indicating the essential role of phosphorylation on AtGTR1. In summary, this study investigated various factors associated with the GLS transport and increased our knowledge on the substrate preferences of AtGTR1. These findings contribute to understanding how the distribution of defense GLSs is regulated in plants and could be used to improve crop quality in agriculture.

Molecular species selectivity of lipid transport creates a mitochondrial sink for di‐unsaturated phospholipids

Mitochondria depend on the import of phospholipid precursors for the biosynthesis of phosphatidylethanolamine (PE) and cardiolipin, yet the mechanism of their transport remains elusive. A dynamic lipidomics approach revealed that mitochondria preferentially import di‐unsaturated phosphatidylserine (PS) for subsequent conversion to PE by the mitochondrial PS decarboxylase Psd1p. Several protein complexes tethering mitochondria to the endomembrane system have been implicated in lipid transport in yeast, including the endoplasmic reticulum (ER)‐mitochondrial encounter structure (ERMES), ER‐membrane complex (EMC), and the vacuole and mitochondria patch (vCLAMP). By limiting the availability of unsaturated phospholipids, we created conditions to investigate the mechanism of lipid transfer and the contributions of the tethering complexes in vivo. Under these conditions, inactivation of ERMES components or of the vCLAMP component Vps39p exacerbated accumulation of saturated lipid acyl chains, indicating that ERMES and Vps39p contribute to the mitochondrial sink for unsaturated acyl chains by mediating transfer of di‐unsaturated phospholipids. These results support the concept that intermembrane lipid flow is rate‐limited by molecular species‐dependent lipid efflux from the donor membrane and driven by the lipid species’ concentration gradient between donor and acceptor membrane.

High-affinity iron and calcium transport pathways are involved in U(VI) uptake in the budding yeast Saccharomyces cerevisiae

Uranium (U) is a naturally-occurring radionuclide that is toxic for all living organisms. To date, the mechanisms of U uptake are far from being understood. Here we provide a direct characterization of the transport machineries capable of transporting U, using the yeast Saccharomyces cerevisiae as a unicellular eukaryote model. First, we evidenced a metabolism-dependent U transport in yeast. Then, competition experiments with essential metals allowed us to identify calcium, iron and copper entry pathways as potential routes for U uptake. The analysis of various metal transport mutants revealed that mutant affected in calcium (mid1Δ and cch1Δ) and Fe(III) (ftr1Δ) transport, exhibited highly reduced U uptake rates and accumulation, demonstrating the implication of the calcium channel Mid1/Cch1 and the iron permease Ftr1 in U uptake. Finally, expression of the Mid1 gene into the mid1Δ mutant restored U uptake levels of the wild type strain, underscoring the central role of the Mid1/Cch1 calcium channel in U absorption process in yeast. Our results also open up the opportunity for rapid screening of U-transporter candidates by functional expression in yeast, before their validation in more complex higher eukaryote model systems.

Characterization of JEN family carboxylate transporters from the acid-tolerant yeast Pichia kudriavzevii and their applications in succinic acid production.

SummaryThe unconventional yeast Pichia kudriavzevii is renowned for its ability to survive at low pH and has been exploited for the industrial production of various organic acids, especially succinic acid (SA). However, P. kudriavzevii can also utilize the di‐ and tricarboxylate intermediates of the Krebs cycle as the sole carbon sources for cell growth, which may adversely affect the extracellular accumulation of SA. Because the carboxylic acid transport machinery of P. kudriavzevii remains poorly understood, here, we focused on studying its SA transportation process from the perspective of mining and characterization of dicarboxylate transporters in a newly isolated acid‐tolerant P. kudriavzevii strain CY902. Through genome sequencing and transcriptome analysis, two JEN family carboxylate transporters (PkJEN2‐1 and PkJEN2‐2) were found to be involved in SA transport. Substrate specificity analysis revealed that both PkJEN proteins are active dicarboxylate transporters, that can effectively import succinate, fumarate and L‐malate into the cell. In addition, PkJEN2‐1 can transport α‐ketoglutarate, while PkJEN2‐2 cannot. Since PkJEN2‐1 shows higher transcript abundance than PkJEN2‐2, its role in dicarboxylate transport is more important than PkJEN2‐2. In addition, PKJEN2‐2 is also responsible for the uptake of citrate. To our best knowledge, this is the first study to show that a JEN2 subfamily transporter is involved in tricarboxylate transport in yeast. A combination of model‐based structure analysis and rational mutagenesis further proved that amino acid residues 392‐403 of the tenth transmembrane span (TMS‐X) of PkJEN2‐2 play an important role in determining the specificity of the tricarboxylate substrate. Moreover, these two PkJEN transporters only exhibited inward transport activity for SA, and simultaneous inactivation of both PkJEN transporters reduced the SA influx, resulting in enhanced extracellular accumulation of SA in the late stage of fermentation. This work provides useful information on the mechanism of di‐/tricarboxylic acid utilization in P. kudriavzevii, which will help improve the organic acid production performance of this microbial chassis.

Functional Analysis of Phosphate Transporter OsPHT4 Family Members in Rice

The transport of phosphate between cytoplasm and subcellular compartments is critical for plant metabolic regulation. We conducted bioinformatic analysis, heterologous expression in yeast, gene expression pattern and subcellular localization analysis to characterize the possible functions of OsPHT4 gene family in rice. Together with the PHT4 genes from higher plants, OsPHT4s can be classified into six distinct groups. OsPHT4;1–OsPHT4;4 are targeted to chloroplasts, and OsPHT4;6-1 and OsPHT4;6-2 are located to Golgi apparatus. OsPHT4 proteins can mediate inorganic phosphate (Pi) transport in yeast. In addition, dynamic transcriptional changes determined by qRT-PCR revealed different expression profiles of OsPHT4 genes in response to phosphate starvation, salicylic acid, abscisic acid and salt stress treatments. These results suggested that OsPHT4 proteins are involved in Pi distribution between the cytoplasm and chloroplast or Golgi apparatus and also involved in stress responses.

AP‐3 vesicle uncoating occurs after HOPS‐dependent vacuole tethering

Heterotetrameric adapter (AP) complexes cooperate with the small GTPase Arf1 or lipids in cargo selection, vesicle formation, and budding at endomembranes in eukaryotic cells. While most AP complexes also require clathrin as the outer vesicle shell, formation of AP‐3‐coated vesicles involved in Golgi‐to‐vacuole transport in yeast has been postulated to depend on Vps41, a subunit of the vacuolar HOPS tethering complex. HOPS has also been identified as the tether of AP‐3 vesicles on vacuoles. To unravel this conundrum of a dual Vps41 function, we anchored Vps41 stably to the mitochondrial outer membrane. By monitoring AP‐3 recruitment, we now show that Vps41 can tether AP‐3 vesicles to mitochondria, yet AP‐3 vesicles can form in the absence of Vps41 or clathrin. By proximity labeling and mass spectrometry, we identify the Arf1 GTPase‐activating protein (GAP) Age2 at the AP‐3 coat and show that tethering, but not fusion at the vacuole can occur without complete uncoating. We conclude that AP‐3 vesicles retain their coat after budding and that their complete uncoating occurs only after tethering at the vacuole.

HAK/KUP/KT family potassium transporter genes are involved in potassium deficiency and stress responses in tea plants (Camellia sinensis L.): expression and functional analysis

BackgroundTea plant is one of the most important non-alcoholic beverage crops worldwide. While potassium (K+) is an essential macronutrient and greatly affects the growth and development of plants, the molecular mechanism underlying K+ uptake and transport in tea plant root, especially under limited-K+ conditions, is still poorly understood. In plants, HAK/KUP/KT family members play a crucial role in K+ acquisition and translocation, growth and development, and response to stresses. Nevertheless, the biological functions of these genes in tea plant are still in mystery, especially their roles in K+ uptake and stress responses.ResultsIn this study, a total of 21 non-redundant HAK/KUP/KT genes (designated as CsHAKs) were identified in tea plant. Phylogenetic and structural analysis classified the CsHAKs into four clusters (I, II, III, IV), containing 4, 8, 4 and 5 genes, respectively. Three major categories of cis-acting elements were found in the promoter regions of CsHAKs. Tissue-specific expression analysis indicated extremely low expression levels in various tissues of cluster I CsHAKs with the exception of a high root expression of CsHAK4 and CsHAK5, a constitutive expression of clusters II and III CsHAKs, and a moderate cluster IV CsHAKs expression. Remarkably, the transcript levels of CsHAKs in roots were significantly induced or suppressed after exposure to K+ deficiency, salt and drought stresses, and phytohormones treatments. Also notably, CsHAK7 was highly expressed in all tissues and was further induced under various stress conditions. Therefore, functional characterization of CsHAK7 was performed, and the results demostrated that CsHAK7 locates on plasma membrane and plays a key role in K+ transport in yeast. Taken together, the results provide promising candidate CsHAKs for further functional studies and contribute to the molecular breeding for new tea plants varieties with highly efficient utilization of K+.ConclusionThis study demonstrated the first genome-wide analysis of CsHAK family genes of tea plant and provides a foundation for understanding the classification and functions of the CsHAKs in tea plants.

GmVTL1a is an iron transporter on the symbiosome membrane of soybean with an important role in nitrogen fixation.

Legumes establish symbiotic relationships with soil bacteria (rhizobia), housed in nodules on roots. The plant supplies carbon substrates and other nutrients to the bacteria in exchange for fixed nitrogen. The exchange occurs across a plant-derived symbiosome membrane (SM), which encloses rhizobia to form a symbiosome. Iron supplied by the plant is crucial for rhizobial enzyme nitrogenase that catalyses nitrogen fixation, but the SM iron transporter has not been identified. We use yeast complementation, real-time PCR and proteomics to study putative soybean (Glycine max) iron transporters GmVTL1a and GmVTL1b and have characterized the role of GmVTL1a using complementation in plant mutants, hairy root transformation and microscopy. GmVTL1a and GmVTL1b are members of the vacuolar iron transporter family and homologous to Lotus japonicus SEN1 (LjSEN1), which is essential for nitrogen fixation. GmVTL1a expression is enhanced in nodule infected cells and both proteins are localized to the SM. GmVTL1a transports iron in yeast and restores nitrogen fixation when expressed in the Ljsen1 mutant. Three GmVTL1a amino acid substitutions that block nitrogen fixation in Ljsen1 plants reduce iron transport in yeast. We conclude GmVTL1a is responsible for transport of iron across the SM to bacteroids and plays a crucial role in the nitrogen-fixing symbiosis.

Diversity of Oligopeptide Transport in Yeast and Its Impact on Adaptation to Winemaking Conditions.

Nitrogen is an essential nutrient for yeasts and its relative abundance is an important modulator of fermentation kinetics. The main sources of nitrogen in food are ammonium and free amino acids, however, secondary sources such as oligopeptides are also important contributors to the nitrogen supply. In yeast, oligopeptide uptake is driven by different families of proton–coupled transporters whose specificity depends on peptide length. Proton-dependent Oligopeptide Transporters (POT) are specific to di- and tri-peptides, whereas the Oligopeptide Transport (OPT) family members import tetra- and pentapeptides. Recently, the novel family of Fungal Oligopeptide Transporters (FOT) has been identified in Saccharomyces cerevisiae wine strains as a result of a horizontal gene transfer from Torulaspora microellipsoides. In natural grape must fermentations with S. cerevisiae, Fots have a broader range of oligopeptide utilization in comparison with non-Fot strains, leading to higher biomass production and better fermentation efficiency. In this review we present the current knowledge on the diversity of oligopeptide transporters in yeast, also discussing how the consumption of oligopeptides provides an adaptive advantage to yeasts within the wine environment.