RBG Motif Bridge-Like Lipid Transport Proteins: Structure, Functions, and Open Questions.

The life of eukaryotic cells requires the transport of lipids between membranes, which are separated by the aqueous environment of the cytosol. Vesicle-mediated traffic along the secretory and endocytic pathways and lipid transfer proteins (LTPs) cooperate in this transport. Until recently, known LTPs were shown to carry one or a few lipids at a time and were thought to mediate transport by shuttle-like mechanisms. Over the last few years, a new family of LTPs has been discovered that is defined by a repeating ß-groove (RBG) rod-like structure with a hydrophobic channel running along their entire length. This structure and the localization of these proteins at membrane contact sites suggest a bridge-like mechanism of lipid transport. Mutations in some of these proteins result in neurodegenerative and developmental disorders. Here we review the known properties and well-established or putative physiological roles of these proteins, and we highlight the many questions that remain open about their functions.

Development and Cell Biology of the Blood-Brain Barrier.

The vertebrate vasculature displays high organotypic specialization, with the structure and function of blood vessels catering to the specific needs of each tissue. A unique feature of the central nervous system (CNS) vasculature is the blood-brain barrier (BBB). The BBB regulates substance influx and efflux to maintain a homeostatic environment for proper brain function. Here, we review the development and cell biology of the BBB, focusing on the cellular and molecular regulation of barrier formation and the maintenance of the BBB through adulthood. We summarize unique features of CNS endothelial cells and highlight recent progress in and general principles of barrier regulation. Finally, we illustrate why a mechanistic understanding of the development and maintenance of the BBB could provide novel therapeutic opportunities for CNS drug delivery.

Structural basis of lipid head group entry to the Kennedy pathway by FLVCR1.

Phosphatidylcholine and phosphatidylethanolamine, the two most abundant phospholipids in mammalian cells, are synthesized de novo by the Kennedy pathway from choline and ethanolamine, respectively1-6. Despite the essential roles of these lipids, the mechanisms that enable the cellular uptake of choline and ethanolamine remain unknown. Here we show that the protein encoded by FLVCR1, whose mutation leads to the neurodegenerative syndrome posterior column ataxia and retinitis pigmentosa7-9, transports extracellular choline and ethanolamine into cells for phosphorylation by downstream kinases to initiate the Kennedy pathway. Structures of FLVCR1 in the presence of choline and ethanolamine reveal that both metabolites bind to a common binding site comprising aromatic and polar residues. Despite binding to a common site, FLVCR1 interacts in different ways with the larger quaternary amine of choline in and with the primary amine of ethanolamine. Structure-guided mutagenesis identified residues that are crucial for the transport of ethanolamine, but dispensable for choline transport, enabling functional separation of the entry points into the two branches of the Kennedy pathway. Altogether, these studies reveal how FLVCR1 is a high-affinity metabolite transporter that serves as the common origin for phospholipid biosynthesis by two branches of the Kennedy pathway.

Phosphate Transport in Epithelial and Nonepithelial Tissue.

Phosphate is an essential nutrient for life and is a critical component of bone formation, a major signaling molecule, and structural component of cell walls. Phosphate is also a component of high-energy compounds (i.e., AMP, ADP, and ATP) and essential for nucleic acid helical structure (i.e., RNA and DNA). Phosphate plays a central role in the process of mineralization, normal serum levels being associated with appropriate bone mineralization, while high and low serum levels are associated with soft tissue calcification. The serum concentration of phosphate and the total body content of phosphate are highly regulated, a process that is accomplished by the coordinated effort of two families of sodium-dependent transporter proteins. The three isoforms of the SLC34 family (SLC34A1-A3) show very restricted tissue expression and regulate intestinal absorption and renal excretion of phosphate. SLC34A2 also regulates the phosphate concentration in multiple lumen fluids including milk, saliva, pancreatic fluid, and surfactant. Both isoforms of the SLC20 family exhibit ubiquitous expression (with some variation as to which one or both are expressed), are regulated by ambient phosphate, and likely serve the phosphate needs of the individual cell. These proteins exhibit similarities to phosphate transporters in nonmammalian organisms. The proteins are nonredundant as mutations in each yield unique clinical presentations. Further research is essential to understand the function, regulation, and coordination of the various phosphate transporters, both the ones described in this review and the phosphate transporters involved in intracellular transport.

YeeD is an essential partner for YeeE-mediated thiosulfate uptake in bacteria and regulates thiosulfate ion decomposition.

Uptake of thiosulfate ions as an inorganic sulfur source from the environment is important for bacterial sulfur assimilation. Recently, a selective thiosulfate uptake pathway involving a membrane protein YeeE (TsuA) in Escherichia coli was characterized. YeeE-like proteins are conserved in some bacteria, archaea, and eukaryotes. However, the precise function of YeeE, along with its potential partner protein in the thiosulfate ion uptake pathway, remained unclear. Here, we assessed selective thiosulfate transport via Spirochaeta thermophila YeeE in vitro and characterized E. coli YeeD (TsuB) as an adjacent and essential protein for YeeE-mediated thiosulfate uptake in vivo. We further showed that S. thermophila YeeD possesses thiosulfate decomposition activity and that a conserved cysteine in YeeD was modified to several forms in the presence of thiosulfate. Finally, the crystal structures of S. thermophila YeeE-YeeD fusion proteins at 3.34-Å and 2.60-Å resolutions revealed their interactions. The association was evaluated by a binding assay using purified S. thermophila YeeE and YeeD. Based on these results, a model of the sophisticated uptake of thiosulfate ions by YeeE and YeeD is proposed.

Candida albicans' inorganic phosphate transport and evolutionary adaptation to phosphate scarcity.

Phosphorus is essential in all cells' structural, metabolic and regulatory functions. For fungal cells that import inorganic phosphate (Pi) up a steep concentration gradient, surface Pi transporters are critical capacitators of growth. Fungi must deploy Pi transporters that enable optimal Pi uptake in pH and Pi concentration ranges prevalent in their environments. Single, triple and quadruple mutants were used to characterize the four Pi transporters we identified for the human fungal pathogen Candida albicans, which must adapt to alkaline conditions during invasion of the host bloodstream and deep organs. A high-affinity Pi transporter, Pho84, was most efficient across the widest pH range while another, Pho89, showed high-affinity characteristics only within one pH unit of neutral. Two low-affinity Pi transporters, Pho87 and Fgr2, were active only in acidic conditions. Only Pho84 among the Pi transporters was clearly required in previously identified Pi-related functions including Target of Rapamycin Complex 1 signaling, oxidative stress resistance and hyphal growth. We used in vitro evolution and whole genome sequencing as an unbiased forward genetic approach to probe adaptation to prolonged Pi scarcity of two quadruple mutant lineages lacking all 4 Pi transporters. Lineage-specific genomic changes corresponded to divergent success of the two lineages in fitness recovery during Pi limitation. Initial, large-scale genomic alterations like aneuploidies and loss of heterozygosity eventually resolved, as populations gained small-scale mutations. Severity of some phenotypes linked to Pi starvation, like cell wall stress hypersensitivity, decreased in parallel to evolving populations' fitness recovery in Pi scarcity, while severity of others like membrane stress responses diverged from Pi scarcity fitness. Among preliminary candidate genes for contributors to fitness recovery, those with links to TORC1 were overrepresented. Since Pi homeostasis differs substantially between fungi and humans, adaptive processes to Pi deprivation may harbor small-molecule targets that impact fungal growth, stress resistance and virulence.

Genetic evidence for functional diversification of gram-negative intermembrane phospholipid transporters.

The outer membrane of gram-negative bacteria is a barrier to chemical and physical stress. Phospholipid transport between the inner and outer membranes has been an area of intense investigation and, in E. coli K-12, it has recently been shown to be mediated by YhdP, TamB, and YdbH, which are suggested to provide hydrophobic channels for phospholipid diffusion, with YhdP and TamB playing the major roles. However, YhdP and TamB have different phenotypes suggesting distinct functions. It remains unclear whether these functions are related to phospholipid metabolism. We investigated a synthetic cold sensitivity caused by deletion of fadR, a transcriptional regulator controlling fatty acid degradation and unsaturated fatty acid production, and yhdP, but not by ΔtamB ΔfadR or ΔydbH ΔfadR. Deletion of tamB recuses the ΔyhdP ΔfadR cold sensitivity further demonstrating the phenotype is related to functional diversification between these genes. The ΔyhdP ΔfadR strain shows a greater increase in cardiolipin upon transfer to the non-permissive temperature and genetically lowering cardiolipin levels can suppress cold sensitivity. These data also reveal a qualitative difference between cardiolipin synthases in E. coli, as deletion of clsA and clsC suppresses cold sensitivity but deletion of clsB does not. Moreover, increased fatty acid saturation is necessary for cold sensitivity and lowering this level genetically or through supplementation of oleic acid suppresses the cold sensitivity of the ΔyhdP ΔfadR strain. Together, our data clearly demonstrate that the diversification of function between YhdP and TamB is related to phospholipid metabolism. Although indirect regulatory effects are possible, we favor the parsimonious hypothesis that YhdP and TamB have differential phospholipid-substrate transport preferences. Thus, our data provide a potential mechanism for independent control of the phospholipid composition of the inner and outer membranes in response to changing conditions based on regulation of abundance or activity of YhdP and TamB.

Molecular basis of accessible plasma membrane cholesterol recognition by the GRAM domain of GRAMD1b.

Cholesterol is essential for cell physiology. Transport of the "accessible" pool of cholesterol from the plasma membrane (PM) to the endoplasmic reticulum (ER) by ER-localized GRAMD1 proteins (GRAMD1a/1b/1c) contributes to cholesterol homeostasis. However, how cells detect accessible cholesterol within the PM remains unclear. We show that the GRAM domain of GRAMD1b, a coincidence detector for anionic lipids, including phosphatidylserine (PS), and cholesterol, possesses distinct but synergistic sites for sensing accessible cholesterol and anionic lipids. We find that a mutation within the GRAM domain of GRAMD1b that is associated with intellectual disability in humans specifically impairs cholesterol sensing. In addition, we identified another point mutation within this domain that enhances cholesterol sensitivity without altering its PS sensitivity. Cell-free reconstitution and cell-based assays revealed that the ability of the GRAM domain to sense accessible cholesterol regulates membrane tethering and determines the rate of cholesterol transport by GRAMD1b. Thus, cells detect the codistribution of accessible cholesterol and anionic lipids in the PM and fine-tune the non-vesicular transport of PM cholesterol to the ER via GRAMD1s.

The high-energy transition state of the glutamate transporter homologue GltPh.

Membrane transporters mediate cellular uptake of nutrients, signaling molecules, and drugs. Their overall mechanisms are often well understood, but the structural features setting their rates are mostly unknown. Earlier single-molecule fluorescence imaging of the archaeal model glutamate transporter homologue GltPh from Pyrococcus horikoshii suggested that the slow conformational transition from the outward- to the inward-facing state, when the bound substrate is translocated from the extracellular to the cytoplasmic side of the membrane, is rate limiting to transport. Here, we provide insight into the structure of the high-energy transition state of GltPh that limits the rate of the substrate translocation process. Using bioinformatics, we identified GltPh gain-of-function mutations in the flexible helical hairpin domain HP2 and applied linear free energy relationship analysis to infer that the transition state structurally resembles the inward-facing conformation. Based on these analyses, we propose an approach to search for allosteric modulators for transporters.

HASTY, the Arabidopsis EXPORTIN5 ortholog, regulates cell-to-cell and vascular microRNA movement.

Plant microRNAs (miRNAs) guide cytosolic post-transcriptional gene silencing of sequence-complementary transcripts within the producing cells, as well as in distant cells and tissues. Here, we used an artificial miRNA-based system (amiRSUL) in Arabidopsis thaliana to explore the still elusive mechanisms of inter-cellular miRNA movement via forward genetics. This screen identified many mutant alleles of HASTY (HST), the ortholog of mammalian EXPORTIN5 (XPO5) with a recently reported role in miRNA biogenesis in Arabidopsis. In both epidermis-peeling and grafting assays, amiRSUL levels were reduced much more substantially in miRNA-recipient tissues than in silencing-emitting tissues. We ascribe this effect to HST controlling cell-to-cell and phloem-mediated movement of the processed amiRSUL, in addition to regulating its biogenesis. While HST is not required for the movement of free GFP or siRNAs, its cell-autonomous expression in amiRSUL-emitting tissues suffices to restore amiRSUL movement independently of its nucleo-cytosolic shuttling activity. By contrast, HST is dispensable for the movement and activity of amiRSUL within recipient tissues. Finally, HST enables movement of endogenous miRNAs that display mostly unaltered steady-state levels in hst mutant tissues. We discuss a role for HST as a hitherto unrecognized regulator of miRNA movement in relation to its recently assigned nuclear function at the nexus of MIRNA transcription and miRNA processing.

High temperature perception in leaves promotes vascular regeneration and graft formation in distant tissues.

Cellular regeneration in response to wounding is fundamental to maintain tissue integrity. Various internal factors including hormones and transcription factors mediate healing, but little is known about the role of external factors. To understand how the environment affects regeneration, we investigated the effects of temperature upon the horticulturally relevant process of plant grafting. We found that elevated temperatures accelerated vascular regeneration in Arabidopsis thaliana and tomato grafts. Leaves were crucial for this effect, as blocking auxin transport or mutating PHYTOCHROME INTERACTING FACTOR 4 (PIF4) or YUCCA2/5/8/9 in the cotyledons abolished the temperature enhancement. However, these perturbations did not affect grafting at ambient temperatures, and temperature enhancement of callus formation and tissue adhesion did not require PIF4, suggesting leaf-derived auxin specifically enhanced vascular regeneration in response to elevated temperatures. We also found that elevated temperatures accelerated the formation of inter-plant vascular connections between the parasitic plant Phtheirospermum japonicum and host Arabidopsis, and this effect required shoot-derived auxin from the parasite. Taken together, our results identify a pathway whereby local temperature perception mediates long distance auxin signaling to modify regeneration, grafting and parasitism. This article has an associated 'The people behind the papers' interview.

Identification of a novel cationic glycolipid in Streptococcus agalactiae that contributes to brain entry and meningitis.

Bacterial membrane lipids are critical for membrane bilayer formation, cell division, protein localization, stress responses, and pathogenesis. Despite their critical roles, membrane lipids have not been fully elucidated for many pathogens. Here, we report the discovery of a novel cationic glycolipid, lysyl-glucosyl-diacylglycerol (Lys-Glc-DAG), which is synthesized in high abundance by the bacterium Streptococcus agalactiae (Group B Streptococcus, GBS). To our knowledge, Lys-Glc-DAG is more positively charged than any other known lipids. Lys-Glc-DAG carries 2 positive net charges per molecule, distinct from the widely described lysylated phospholipid lysyl-phosphatidylglycerol (Lys-PG) that carries one positive net charge due to the presence of a negatively charged phosphate moiety. We use normal phase liquid chromatography (NPLC) coupled with electrospray ionization (ESI) high-resolution tandem mass spectrometry (HRMS/MS) and genetic approaches to determine that Lys-Glc-DAG is synthesized by the enzyme MprF in GBS, which covalently modifies the neutral glycolipid Glc-DAG with the cationic amino acid lysine. GBS is a leading cause of neonatal meningitis, which requires traversal of the endothelial blood-brain barrier (BBB). We demonstrate that GBS strains lacking mprF exhibit a significant decrease in the ability to invade BBB endothelial cells. Further, mice challenged with a GBSΔmprF mutant developed bacteremia comparably to wild-type (WT) infected mice yet had less recovered bacteria from brain tissue and a lower incidence of meningitis. Thus, our data suggest that Lys-Glc-DAG may contribute to bacterial uptake into host cells and disease progression. Importantly, our discovery provides a platform for further study of cationic lipids at the host-pathogen interface.

Polar auxin transport modulates early leaf flattening.

The flattened leaf form is an important adaptation for efficient photosynthesis, and the developmental process of flattened leaves has been intensively studied. Classic microsurgery studies in potato and tomato suggest that the shoot apical meristem (SAM) communicates with the leaf primordia to promote leaf blade formation. More recently, it was found that polar auxin transport (PAT) could mediate this communication. However, it is unclear how the expression of leaf patterning genes is tailored by PAT routes originating from SAM. By combining experimental observations and computer model simulations, we show that microsurgical incisions and local inhibition of PAT in tomato interfere with auxin transport toward the leaf margins, reducing auxin response levels and altering the leaf blade shape. Importantly, oval auxin responses result in the bipolar expression of SlLAM1 that determines leaf blade formation. Furthermore, wounding caused by incisions promotes degradation of SlREV, a known regulator of leaf polarity. Additionally, computer simulations suggest that local auxin biosynthesis in early leaf primordia could remove necessity for external auxin supply originating from SAM, potentially explaining differences between species. Together, our findings establish how PAT near emerging leaf primordia determines spatial auxin patterning and refines SlLAM1 expression in the leaf margins to guide leaf flattening.

Absence of YhdP, TamB, and YdbH leads to defects in glycerophospholipid transport and cell morphology in Gram-negative bacteria.

The outer membrane (OM) of Gram-negative bacteria provides the cell with a formidable barrier that excludes external threats. The two major constituents of this asymmetric barrier are lipopolysaccharide (LPS) found in the outer leaflet, and glycerophospholipids (GPLs) in the inner leaflet. Maintaining the asymmetric nature and balance of LPS to GPLs in the OM is critical for bacterial viability. The biosynthetic pathways of LPS and GPLs are well characterized, but unlike LPS transport, how GPLs are translocated to the OM remains enigmatic. Understanding this aspect of cell envelope biology could provide a foundation for new antibacterial therapies. Here, we report that YhdP and its homologues, TamB and YdbH, members of the "AsmA-like" family, are critical for OM integrity and necessary for proper GPL transport to the OM. The absence of the two largest AsmA-like proteins (YhdP and TamB) leads to cell lysis and antibiotic sensitivity, phenotypes that are rescued by reducing LPS synthesis. We also find that yhdP, tamB double mutants shed excess LPS through outer membrane vesicles, presumably to maintain OM homeostasis when normal anterograde GPL transport is disrupted. Moreover, a yhdP, tamB, ydbH triple mutant is synthetically lethal, but if GPL transport is partially restored by overexpression of YhdP, the cell shape adjusts to accommodate increased membrane content as the cell accumulates GPLs in the IM. Our results therefore suggest a model in which "AsmA-like" proteins transport GPLs to the OM, and when hindered, changes in cell shape and shedding of excess LPS aids in maintaining OM asymmetry.

A mechanism of self-lipid endocytosis mediated by the receptor Mincle.

Cellular lipid uptake (through endocytosis) is a basic physiological process. Dysregulation of this process underlies the pathogenesis of diseases such as atherosclerosis, obesity, diabetes, and cancer. However, to date, only some mechanisms of lipid endocytosis have been discovered. Here, we show a previously unknown mechanism of lipid cargo uptake into cells mediated by the receptor Mincle. We found that the receptor Mincle, previously shown to be a pattern recognition receptor of the innate immune system, tightly binds a range of self-lipids. Moreover, we revealed the minimal molecular motif in lipids that is sufficient for Mincle recognition. Superresolution microscopy showed that Mincle forms vesicles in cytoplasm and colocalizes with added fluorescent lipids in endothelial cells but does not colocalize with either clathrin or caveolin-1, and the added lipids were predominantly incorporated in vesicles that expressed Mincle. Using a model of ganglioside GM3 uptake in brain vessel endothelial cells, we show that the knockout of Mincle led to a dramatic decrease in lipid endocytosis. Taken together, our results have revealed a fundamental lipid endocytosis pathway, which we call Mincle-mediated endocytosis (MiME), and indicate a prospective target for the treatment of disorders of lipid metabolism, which are rapidly increasing in prevalence.

Glycolipid transfer protein knockout disrupts vesicle trafficking to the plasma membrane.

The glycolipid transfer protein (GLTP) has been linked to many cellular processes aside from its best-known in vitro function as a lipid transport protein. It has been proposed to act as a sensor and regulator of glycosphingolipid homeostasis in cells. Furthermore, through its previously determined interaction with the endoplasmic reticulum membrane protein VAP-A (vesicle-associated membrane protein-associated protein A), GLTP may also be involved in facilitating vesicular transport in cells. In this study, we characterized the phenotype of CRISPR/Cas9-mediated GLTP KO HeLa cells. We showed that motility, three-dimensional growth, and cellular metabolism were all altered by GLTP knockout. Expression of a GLTP mutant incapable of binding VAP disrupted cell spheroid formation, indicating that the GLTP-VAP interaction is linked to cellular adhesion, cohesion, and three-dimensional growth. Most notably, we found evidence that GLTP, through its interaction with VAP-A, affects vesicular trafficking, marking the first cellular process discovered to be directly impacted by a change in GLTP expression.

Arabidopsis callus grafts: a system to study symplasmic intercellular macromolecular transport and gene silencing spread.

In the present study, we present callus grafting, comprising a method for reproducibly generating tissue chimeras from callus cultures of Arabidopsis thaliana. In this way, callus cultures of different genetic backgrounds may be co-cultivated such that cell-to-cell connectivity is achieved as a chimeric tissue is formed. To track intercellular connectivity and transport between non-clonal callus cells, we used transgenic lines expressing fluorescently tagged mobile and non-mobile fusion constructs. Using fluorescently-labelled reporter lines that label plasmodesmata, we show that secondary complex plasmodesmata are present at the cell walls of connected cells. We use this system to investigate cell-to-cell transport across the callus graft junction and show that different proteins and RNAs are mobile between non-clonal callus cells. Finally, we take advantage of the callus culture system to probe intercellular connectivity of grafted leaf and root calli and the effect of different light regimes of cell-to-cell transport. Taking advantage of the ability of callus to be cultivated in the complete absence of light, we show that the rate of silencing spread is significantly decreased in chimeric calli cultivated in total darkness. We propose that callus grafting is a fast and reliable method for analysing the capacity of a macromolecule to be exchanged between cells independent of the vasculature.

AQP1 Promoter Variant, Water Transport, and Outcomes in Peritoneal Dialysis.

BACKGROUND: Variability in ultrafiltration influences prescriptions and outcomes in patients with kidney failure who are treated with peritoneal dialysis. Variants in AQP1, the gene that encodes the archetypal water channel aquaporin-1, may contribute to that variability. METHODS: We gathered clinical and genetic data from 1851 patients treated with peritoneal dialysis in seven cohorts to determine whether AQP1 variants were associated with peritoneal ultrafiltration and with a risk of the composite of death or technique failure (i.e., transfer to hemodialysis). We performed studies in cells, mouse models, and samples obtained from humans to characterize an AQP1 variant and investigate mitigation strategies. RESULTS: The common AQP1 promoter variant rs2075574 was associated with peritoneal ultrafiltration. Carriers of the TT genotype at rs2075574 (10 to 16% of patients) had a lower mean (±SD) net ultrafiltration level than carriers of the CC genotype (35 to 47% of patients), both in the discovery phase (506±237 ml vs. 626±283 ml, P = 0.007) and in the validation phase (368±603 ml vs. 563±641 ml, P = 0.003). After a mean follow-up of 944 days, 139 of 898 patients (15%) had died and 280 (31%) had been transferred to hemodialysis. TT carriers had a higher risk of the composite of death or technique failure than CC carriers (adjusted hazard ratio, 1.70; 95% confidence interval [CI], 1.24 to 2.33; P = 0.001), as well as a higher risk of death from any cause (24% vs. 15%, P = 0.03). In mechanistic studies, the rs2075574 risk variant was associated with decreases in AQP1 promoter activity, aquaporin-1 expression, and glucose-driven osmotic water transport. The use of a colloid osmotic agent mitigated the effects of the risk variant. CONCLUSIONS: A common variant in AQP1 was associated with decreased ultrafiltration and an increased risk of death or technique failure among patients treated with peritoneal dialysis. (Funded by the Swiss National Science Foundation and others.).

Characterization and stress-responsive regulation of CmPHT1 genes involved in phosphate uptake and transport in Melon (Cucumis melo L.).

BACKGROUND: Phosphorus (P) deficiency, a major nutrient stress, greatly hinders plant growth. Phosphate (Pi) uptake in plant roots relies on PHT1 family transporters. However, melon (Cucumis melo L.) lacks comprehensive identification and characterization of PHT1 genes, particularly their response patterns under diverse stresses. RESULTS: This study identified and analyzed seven putative CmPHT1 genes on chromosomes 3, 4, 5, 6, and 7 using the melon genome. Phylogenetic analysis revealed shared motifs, domain compositions, and evolutionary relationships among genes with close histories. Exon number varied from 1 to 3. Collinearity analysis suggested segmental and tandem duplications as the primary mechanisms for CmPHT1 gene family expansion. CmPHT1;4 and CmPHT1;5 emerged as a tandemly duplicated pair. Analysis of cis-elements in CmPHT1 promoters identified 14 functional categories, including putative PHR1-binding sites (P1BS) in CmPHT1;4, CmPHT1;6, and CmPHT1;7. We identified that three WRKY transcription factors regulated CmPHT1;5 expression by binding to its W-box element. Notably, CmPHT1 promoters harbored cis-elements responsive to hormones and abiotic factors. Different stresses regulated CmPHT1 expression differently, suggesting that the adjusted expression patterns might contribute to plant adaptation. CONCLUSIONS: This study unveils the characteristics, evolutionary diversity, and stress responsiveness of CmPHT1 genes in melon. These findings lay the foundation for in-depth investigations into their functional mechanisms in Cucurbitaceae crops.

The Plasmodiophora brassicae Golgi-localized UPF0016 protein PbGDT1 mediates calcium but not manganese transport in yeast and Nicotiana benthamiana.

Manganese and calcium homeostasis and signalling, in eukaryotic organisms, are regulated through membrane located pumps, channels and exchangers, including the Mn2+/Ca2+ uncharacterized protein family 0016 (UPF0016). Here we show that Plasmodiophora brassicae PbGDT1 is a member of the UPF0016 and an ortholog of Saccharomyces cerevisiae Gdt1p (GCR Dependent Translation Factor 1) protein involved in manganese homeostasis as well as the calcium mediated stress response in yeast. PbGDT1 complemented the ScGdt1p and ScPMR1 (Ca2+ ATPase) double null mutant under elevated calcium stress but not under elevated manganese conditions. In both yeast and Nicotiana benthamiana, PbGDT1 localizes to the Golgi apparatus, with additional ER association in N. benthamiana. Expression of PbGDT1 in N. benthamiana, suppresses BAX-triggered cell death, further highlighting the importance of calcium homeostasis in maintaining cell physiology and integrity in a stress environment.