Nα-acetyltransferase NAA50 mediates plant immunity independent of the Nα-acetyltransferase A complex.

In humans and plants, 40% of the proteome is co-translationally acetylated at the N-terminus by a single Nα-acetyltransferase (Nat) termed NatA. The core NatA complex is comprised of the catalytic subunit Nα- acetyltransferase 10 (NAA10) and the ribosome-anchoring subunit NAA15. The regulatory subunit Huntingtin Yeast Partner K (HYPK) and the acetyltransferase NAA50 join this complex in humans. Even though both are conserved in Arabidopsis (Arabidopsis thaliana), only AtHYPK is known to interact with AtNatA. Here we uncover the AtNAA50 interactome and provide evidence for the association of AtNAA50 with NatA at ribosomes. In agreement with the latter, a split-luciferase approach demonstrated close proximity of AtNAA50 and AtNatA in planta. Despite their interaction, AtNatA/HYPK and AtNAA50 exerted different functions in vivo. Unlike NatA/HYPK, AtNAA50 did not modulate drought-tolerance or promote protein stability. Instead, transcriptome and proteome analyses of a novel AtNAA50-depleted mutant (amiNAA50) implied that AtNAA50 negatively regulates plant immunity. Indeed, amiNAA50 plants exhibited enhanced resistance to oomycetes and bacterial pathogens. In contrast to what was observed in NatA-depleted mutants, this resistance was independent of an accumulation of salicylic acid prior to pathogen exposure. Our study dissects the in vivo function of the NatA interactors HYPK and NAA50 and uncovers NatA-independent roles for NAA50 in plants.

A single-sample workflow for joint metabolomic and proteomic analysis of clinical specimens.

Understanding the interplay of the proteome and the metabolome helps to understand cellular regulation and response. To enable robust inferences from such multi-omics analyses, we introduced and evaluated a workflow for combined proteome and metabolome analysis starting from a single sample. Specifically, we integrated established and individually optimized protocols for metabolomic and proteomic profiling (EtOH/MTBE and autoSP3, respectively) into a unified workflow (termed MTBE-SP3), and took advantage of the fact that the protein residue of the metabolomic sample can be used as a direct input for proteome analysis. We particularly evaluated the performance of proteome analysis in MTBE-SP3, and demonstrated equivalence of proteome profiles irrespective of prior metabolite extraction. In addition, MTBE-SP3 combines the advantages of EtOH/MTBE and autoSP3 for semi-automated metabolite extraction and fully automated proteome sample preparation, respectively, thus advancing standardization and scalability for large-scale studies. We showed that MTBE-SP3 can be applied to various biological matrices (FFPE tissue, fresh-frozen tissue, plasma, serum and cells) to enable implementation in a variety of clinical settings. To demonstrate applicability, we applied MTBE-SP3 and autoSP3 to a lung adenocarcinoma cohort showing consistent proteomic alterations between tumour and non-tumour adjacent tissue independent of the method used. Integration with metabolomic data obtained from the same samples revealed mitochondrial dysfunction in tumour tissue through deregulation of OGDH, SDH family enzymes and PKM. In summary, MTBE-SP3 enables the facile and reliable parallel measurement of proteins and metabolites obtained from the same sample, benefiting from reduced sample variation and input amount. This workflow is particularly applicable for studies with limited sample availability and offers the potential to enhance the integration of metabolomic and proteomic datasets.

Author Correction: BCAT1 restricts αKG levels in AML stem cells leading to IDHmut-like DNA hypermethylation.

In Extended Data Fig. 1a of this Letter, the flow cytometry plot depicting the surface phenotype of AML sample DD08 was a duplicate of the plot for AML sample DD06. Supplementary Data 4 has been added to the Supplementary Information of the original Letter to clarify the proteome data acquisition and presentation. The original Letter has been corrected online.

BCAT1 restricts αKG levels in AML stem cells leading to IDHmut-like DNA hypermethylation.

The branched-chain amino acid (BCAA) pathway and high levels of BCAA transaminase 1 (BCAT1) have recently been associated with aggressiveness in several cancer entities. However, the mechanistic role of BCAT1 in this process remains largely uncertain. Here, by performing high-resolution proteomic analysis of human acute myeloid leukaemia (AML) stem-cell and non-stem-cell populations, we find the BCAA pathway enriched and BCAT1 protein and transcripts overexpressed in leukaemia stem cells. We show that BCAT1, which transfers α-amino groups from BCAAs to α-ketoglutarate (αKG), is a critical regulator of intracellular αKG homeostasis. Further to its role in the tricarboxylic acid cycle, αKG is an essential cofactor for αKG-dependent dioxygenases such as Egl-9 family hypoxia inducible factor 1 (EGLN1) and the ten-eleven translocation (TET) family of DNA demethylases. Knockdown of BCAT1 in leukaemia cells caused accumulation of αKG, leading to EGLN1-mediated HIF1α protein degradation. This resulted in a growth and survival defect and abrogated leukaemia-initiating potential. By contrast, overexpression of BCAT1 in leukaemia cells decreased intracellular αKG levels and caused DNA hypermethylation through altered TET activity. AML with high levels of BCAT1 (BCAT1high) displayed a DNA hypermethylation phenotype similar to cases carrying a mutant isocitrate dehydrogenase (IDHmut), in which TET2 is inhibited by the oncometabolite 2-hydroxyglutarate. High levels of BCAT1 strongly correlate with shorter overall survival in IDHWTTET2WT, but not IDHmut or TET2mut AML. Gene sets characteristic for IDHmut AML were enriched in samples from patients with an IDHWTTET2WTBCAT1high status. BCAT1high AML showed robust enrichment for leukaemia stem-cell signatures, and paired sample analysis showed a significant increase in BCAT1 levels upon disease relapse. In summary, by limiting intracellular αKG, BCAT1 links BCAA catabolism to HIF1α stability and regulation of the epigenomic landscape, mimicking the effects of IDH mutations. Our results suggest the BCAA-BCAT1-αKG pathway as a therapeutic target to compromise leukaemia stem-cell function in patients with IDHWTTET2WT AML.

Redox-mediated kick-start of mitochondrial energy metabolism drives resource-efficient seed germination.

Seeds preserve a far developed plant embryo in a quiescent state. Seed metabolism relies on stored resources and is reactivated to drive germination when the external conditions are favorable. Since the switchover from quiescence to reactivation provides a remarkable case of a cell physiological transition we investigated the earliest events in energy and redox metabolism of Arabidopsis seeds at imbibition. By developing fluorescent protein biosensing in intact seeds, we observed ATP accumulation and oxygen uptake within minutes, indicating rapid activation of mitochondrial respiration, which coincided with a sharp transition from an oxidizing to a more reducing thiol redox environment in the mitochondrial matrix. To identify individual operational protein thiol switches, we captured the fast release of metabolic quiescence in organello and devised quantitative iodoacetyl tandem mass tag (iodoTMT)-based thiol redox proteomics. The redox state across all Cys peptides was shifted toward reduction from 27.1% down to 13.0% oxidized thiol. A large number of Cys peptides (412) were redox switched, representing central pathways of mitochondrial energy metabolism, including the respiratory chain and each enzymatic step of the tricarboxylic acid (TCA) cycle. Active site Cys peptides of glutathione reductase 2, NADPH-thioredoxin reductase a/b, and thioredoxin-o1 showed the strongest responses. Germination of seeds lacking those redox proteins was associated with markedly enhanced respiration and deregulated TCA cycle dynamics suggesting decreased resource efficiency of energy metabolism. Germination in aged seeds was strongly impaired. We identify a global operation of thiol redox switches that is required for optimal usage of energy stores by the mitochondria to drive efficient germination.

The function of glutaredoxin GRXS15 is required for lipoyl-dependent dehydrogenases in mitochondria.

Iron-sulfur (Fe-S) clusters are ubiquitous cofactors in all life and are used in a wide array of diverse biological processes, including electron transfer chains and several metabolic pathways. Biosynthesis machineries for Fe-S clusters exist in plastids, the cytosol, and mitochondria. A single monothiol glutaredoxin (GRX) is involved in Fe-S cluster assembly in mitochondria of yeast and mammals. In plants, the role of the mitochondrial homolog GRXS15 has only partially been characterized. Arabidopsis (Arabidopsis thaliana) grxs15 null mutants are not viable, but mutants complemented with the variant GRXS15 K83A develop with a dwarf phenotype similar to the knockdown line GRXS15amiR. In an in-depth metabolic analysis of the variant and knockdown GRXS15 lines, we show that most Fe-S cluster-dependent processes are not affected, including biotin biosynthesis, molybdenum cofactor biosynthesis, the electron transport chain, and aconitase in the tricarboxylic acid (TCA) cycle. Instead, we observed an increase in most TCA cycle intermediates and amino acids, especially pyruvate, glycine, and branched-chain amino acids (BCAAs). Additionally, we found an accumulation of branched-chain α-keto acids (BCKAs), the first degradation products resulting from transamination of BCAAs. In wild-type plants, pyruvate, glycine, and BCKAs are all metabolized through decarboxylation by mitochondrial lipoyl cofactor (LC)-dependent dehydrogenase complexes. These enzyme complexes are very abundant, comprising a major sink for LC. Because biosynthesis of LC depends on continuous Fe-S cluster supply to lipoyl synthase, this could explain why LC-dependent processes are most sensitive to restricted Fe-S supply in grxs15 mutants.

Abrogating GPT2 in triple-negative breast cancer inhibits tumor growth and promotes autophagy.

Uncontrolled proliferation and altered metabolic reprogramming are hallmarks of cancer. Active glycolysis and glutaminolysis are characteristic features of these hallmarks and required for tumorigenesis. A fine balance between cancer metabolism and autophagy is a prerequisite of homeostasis within cancer cells. Here we show that glutamate pyruvate transaminase 2 (GPT2), which serves as a pivot between glycolysis and glutaminolysis, is highly upregulated in aggressive breast cancers, particularly the triple-negative breast cancer subtype. Abrogation of this enzyme results in decreased tricarboxylic acid cycle intermediates, which promotes the rewiring of glucose carbon atoms and alterations in nutrient levels. Concordantly, loss of GPT2 results in an impairment of mechanistic target of rapamycin complex 1 activity as well as the induction of autophagy. Furthermore, in vivo xenograft studies have shown that autophagy induction correlates with decreased tumor growth and that markers of induced autophagy correlate with low GPT2 levels in patient samples. Taken together, these findings indicate that cancer cells have a close network between metabolic and nutrient sensing pathways necessary to sustain tumorigenesis and that aminotransferase reactions play an important role in maintaining this balance.

Dual lysine and N-terminal acetyltransferases reveal the complexity underpinning protein acetylation.

Protein acetylation is a highly frequent protein modification. However, comparatively little is known about its enzymatic machinery. N-α-acetylation (NTA) and ε-lysine acetylation (KA) are known to be catalyzed by distinct families of enzymes (NATs and KATs, respectively), although the possibility that the same GCN5-related N-acetyltransferase (GNAT) can perform both functions has been debated. Here, we discovered a new family of plastid-localized GNATs, which possess a dual specificity. All characterized GNAT family members display a number of unique features. Quantitative mass spectrometry analyses revealed that these enzymes exhibit both distinct KA and relaxed NTA specificities. Furthermore, inactivation of GNAT2 leads to significant NTA or KA decreases of several plastid proteins, while proteins of other compartments were unaffected. The data indicate that these enzymes have specific protein targets and likely display partly redundant selectivity, increasing the robustness of the acetylation process in vivo. In summary, this study revealed a new layer of complexity in the machinery controlling this prevalent modification and suggests that other eukaryotic GNATs may also possess these previously underappreciated broader enzymatic activities.

A Novel UPLC-MS/MS Method Identifies Organ-Specific Dipeptide Profiles.

BACKGROUND: Amino acids have a central role in cell metabolism, and intracellular changes contribute to the pathogenesis of various diseases, while the role and specific organ distribution of dipeptides is largely unknown. METHOD: We established a sensitive, rapid and reliable UPLC-MS/MS method for quantification of 36 dipeptides. Dipeptide patterns were analyzed in brown and white adipose tissues, brain, eye, heart, kidney, liver, lung, muscle, sciatic nerve, pancreas, spleen and thymus, serum and urine of C57BL/6N wildtype mice and related to the corresponding amino acid profiles. RESULTS: A total of 30 out of the 36 investigated dipeptides were detected with organ-specific distribution patterns. Carnosine and anserine were most abundant in all organs, with the highest concentrations in muscles. In liver, Asp-Gln and Ala-Gln concentrations were high, in the spleen and thymus, Glu-Ser and Gly-Asp. In serum, dipeptide concentrations were several magnitudes lower than in organ tissues. In all organs, dipeptides with C-terminal proline (Gly-Pro and Leu-Pro) were present at higher concentrations than dipeptides with N-terminal proline (Pro-Gly and Pro-Leu). Organ-specific amino acid profiles were related to the dipeptide profile with several amino acid concentrations being related to the isomeric form of the dipeptides. Aspartate, histidine, proline and serine tissue concentrations correlated with dipeptide concentrations, when the amino acids were present at the C- but not at the N-terminus. CONCLUSION: Our multi-dipeptide quantification approach demonstrates organ-specific dipeptide distribution. This method allows us to understand more about the dipeptide metabolism in disease or in healthy state.

Prognostic associations of circulating phytoestrogens and biomarker changes in long-term survivors of postmenopausal breast cancer.

Lignans are associated with improved postmenopausal breast cancer (BC) survival, but whether these associations, particularly with enterolactone (major lignan metabolite), persist over time is unclear. Little is known about other phytoestrogens on prognosis in long-term survivors. The study examines associations of prognosis with 1) circulating postdiagnosis enterolactone, 2) eight circulating phytoestrogen metabolites, and 3) changes in enterolactone and genistein. In a German cohort of 2,105 postmenopausal BC patients with blood samples collected at recruitment 2002-2005 (baseline) and re-interview in 2009 (follow-up), delay-entry Cox proportional hazards regression was used. Landmark analysis showed that circulating enterolactone (log2) associations with 5-year survival changed over time, with strongest hazard ratios of 0.89 (95% CI, 0.80-0.99) at blood draw (BD) and 0.86 (0.77-0.97) at 2 years post-BD for BC mortality, and 0.87 (0.80-0.95) at BD and 0.84 (0.76-0.92) at 3 years post-BD for all-cause mortality, which attenuated thereafter. In long-term survivors, increasing concentrations of genistein (1.17, 1.01-1.36), resveratrol (1.19, 1.02-1.40), and luteolin (1.96, 1.07-3.58) measured in follow-up blood samples were associated with poorer subsequent prognosis. Neither enterolactone at follow-up nor changes in enterolactone/genistein were associated with prognosis. Large long-term longitudinal studies with multiple phytoestrogen measurements are required to understand long-term effects of phytoestrogens after BC.

Plant glutathione biosynthesis revisited: redox-mediated activation of glutamylcysteine ligase does not require homo-dimerization.

Plant γ-glutamylcysteine ligase (GCL), catalyzing the first and tightly regulated step of glutathione (GSH) biosynthesis, is redox-activated via formation of an intramolecular disulfide bond. In vitro, redox-activation of recombinant GCL protein causes formation of homo-dimers. Here, we have investigated whether dimerization occurs in vivo and if so whether it contributes to redox-activation. FPLC analysis indicated that recombinant redox-activated WT (wild type) AtGCL dissociates into monomers at concentrations below 10-6 M, i.e. below the endogenous AtGCL concentration in plastids, which was estimated to be in the micromolar range. Thus, dimerization of redox-activated GCL is expected to occur in vivo To determine the possible impact of dimerization on redox-activation, AtGCL mutants were generated in which salt bridges or hydrophobic interactions at the dimer interface were interrupted. WT AtGCL and mutant proteins were analyzed by non-reducing SDS-PAGE to address their redox state and probed by FPLC for dimerization status. Furthermore, their substrate kinetics (KM, Vmax) were compared. The results indicate that dimer formation is not required for redox-mediated enzyme activation. Also, crystal structure analysis confirmed that dimer formation does not affect binding of GSH as competitive inhibitor. Whether dimerization affects other enzyme properties, e.g. GCL stability in vivo, remains to be investigated.

Inhibition of Endothelial Notch Signaling Impairs Fatty Acid Transport and Leads to Metabolic and Vascular Remodeling of the Adult Heart.

BACKGROUND: Nutrients are transported through endothelial cells before being metabolized in muscle cells. However, little is known about the regulation of endothelial transport processes. Notch signaling is a critical regulator of metabolism and angiogenesis during development. Here, we studied how genetic and pharmacological manipulation of endothelial Notch signaling in adult mice affects endothelial fatty acid transport, cardiac angiogenesis, and heart function. METHODS: Endothelial-specific Notch inhibition was achieved by conditional genetic inactivation of Rbp-jκ in adult mice to analyze fatty acid metabolism and heart function. Wild-type mice were treated with neutralizing antibodies against the Notch ligand Delta-like 4. Fatty acid transport was studied in cultured endothelial cells and transgenic mice. RESULTS: Treatment of wild-type mice with Delta-like 4 neutralizing antibodies for 8 weeks impaired fractional shortening and ejection fraction in the majority of mice. Inhibition of Notch signaling specifically in the endothelium of adult mice by genetic ablation of Rbp-jκ caused heart hypertrophy and failure. Impaired heart function was preceded by alterations in fatty acid metabolism and an increase in cardiac blood vessel density. Endothelial Notch signaling controlled the expression of endothelial lipase, Angptl4, CD36, and Fabp4, which are all needed for fatty acid transport across the vessel wall. In endothelial-specific Rbp-jκ-mutant mice, lipase activity and transendothelial transport of long-chain fatty acids to muscle cells were impaired. In turn, lipids accumulated in the plasma and liver. The attenuated supply of cardiomyocytes with long-chain fatty acids was accompanied by higher glucose uptake, increased concentration of glycolysis intermediates, and mTOR-S6K signaling. Treatment with the mTOR inhibitor rapamycin or displacing glucose as cardiac substrate by feeding a ketogenic diet prolonged the survival of endothelial-specific Rbp-jκ-deficient mice. CONCLUSIONS: This study identifies Notch signaling as a novel regulator of fatty acid transport across the endothelium and as an essential repressor of angiogenesis in the adult heart. The data imply that the endothelium controls cardiomyocyte metabolism and function.

Distribution of control in the sulfur assimilation in Arabidopsis thaliana depends on environmental conditions.

Sulfur assimilation is central to the survival of plants and has been studied under different environmental conditions. Multiple studies have been published trying to determine rate-limiting or controlling steps in this pathway. However, the picture remains inconclusive with at least two different enzymes proposed to represent such rate-limiting steps. Here, we used computational modeling to gain an integrative understanding of the distribution of control in the sulfur assimilation pathway of Arabidopsis thaliana. For this purpose, we set up a new ordinary differential equation (ODE)-based, kinetic model of sulfur assimilation encompassing all biochemical reactions directly involved in this process. We fitted the model to published experimental data and produced a model ensemble to deal with parameter uncertainties. The ensemble was validated against additional published experimental data. We used the model ensemble to subsequently analyse the control pattern and robustly identified a set of processes that share the control in this pathway under standard conditions. Interestingly, the pattern of control is dynamic and not static, that is it changes with changing environmental conditions. Therefore, while adenosine-5'-phosphosulfate reductase (APR) and sulfite reductase (SiR) share control under standard laboratory conditions, APR takes over an even more dominant role under sulfur starvation conditions.

Arabidopsis glutathione reductase 2 is indispensable in plastids, while mitochondrial glutathione is safeguarded by additional reduction and transport systems.

A highly negative glutathione redox potential (EGSH ) is maintained in the cytosol, plastids and mitochondria of plant cells to support fundamental processes, including antioxidant defence, redox regulation and iron-sulfur cluster biogenesis. Out of two glutathione reductase (GR) proteins in Arabidopsis, GR2 is predicted to be dual-targeted to plastids and mitochondria, but its differential roles in these organelles remain unclear. We dissected the role of GR2 in organelle glutathione redox homeostasis and plant development using a combination of genetic complementation and stacked mutants, biochemical activity studies, immunogold labelling and in vivo biosensing. Our data demonstrate that GR2 is dual-targeted to plastids and mitochondria, but embryo lethality of gr2 null mutants is caused specifically in plastids. Whereas lack of mitochondrial GR2 leads to a partially oxidised glutathione pool in the matrix, the ATP-binding cassette (ABC) transporter ATM3 and the mitochondrial thioredoxin system provide functional backup and maintain plant viability. We identify GR2 as essential in the plastid stroma, where it counters GSSG accumulation and developmental arrest. By contrast a functional triad of GR2, ATM3 and the thioredoxin system in the mitochondria provides resilience to excessive glutathione oxidation.

Impact of pulsed UV-B stress exposure on plant performance: How recovery periods stimulate secondary metabolism while reducing adaptive growth attenuation.

Upon continuous stress exposure, plants display attenuated metabolic stress responses due to regulatory feedback loops. Here, we have tested the hypothesis that pulsed stress exposure with intervening recovery periods should affect these feedback loops, thereby causing increased accumulation of stress-induced metabolites. The response of Arabidopsis plantlets to continuous UV-B exposure (Cuv ) was compared with that of pulsed UV-B exposure (Puv ). The differential responses to Puv versus Cuv were monitored at the level of gene expression and metabolite accumulation, using wild type (WT) and different mutant lines. In comparison with Cuv , Puv increased sinapyl and flavonol (S + F) content, whereas adaptive growth attenuation was reduced. Furthermore, in a myb4 mutant (AtMYB4, repressor-type R2R3-MYB transcription factor), the S + F content was increased only for Cuv , but not beyond the level for Puv observed in WT. These observations and the ability of AtMYB4 to repress AtMYB12/AtMYB111-mediated activation of target gene promoters (pCHS and pFLS) indicate that the increase of S + F content after Puv observed in WT plants results from reduced feedback inhibition by AtMYB4. The results support the notion that stress-induced metabolic changes not necessarily cause a growth penalty. Furthermore, the observed Puv -induced increase in flavonol accumulation may stimulate reevaluation of commercial plant production practices.

Branched-chain ketoacids secreted by glioblastoma cells via MCT1 modulate macrophage phenotype.

Elevated amino acid catabolism is common to many cancers. Here, we show that glioblastoma are excreting large amounts of branched-chain ketoacids (BCKAs), metabolites of branched-chain amino acid (BCAA) catabolism. We show that efflux of BCKAs, as well as pyruvate, is mediated by the monocarboxylate transporter 1 (MCT1) in glioblastoma. MCT1 locates in close proximity to BCKA-generating branched-chain amino acid transaminase 1, suggesting possible functional interaction of the proteins. Using in vitro models, we demonstrate that tumor-excreted BCKAs can be taken up and re-aminated to BCAAs by tumor-associated macrophages. Furthermore, exposure to BCKAs reduced the phagocytic activity of macrophages. This study provides further evidence for the eminent role of BCAA catabolism in glioblastoma by demonstrating that tumor-excreted BCKAs might have a direct role in tumor immune suppression. Our data further suggest that the anti-proliferative effects of MCT1 knockdown observed by others might be related to the blocked excretion of BCKAs.

Extensive Regulation of Diurnal Transcription and Metabolism by Glucocorticoids.

Altered daily patterns of hormone action are suspected to contribute to metabolic disease. It is poorly understood how the adrenal glucocorticoid hormones contribute to the coordination of daily global patterns of transcription and metabolism. Here, we examined diurnal metabolite and transcriptome patterns in a zebrafish glucocorticoid deficiency model by RNA-Seq, NMR spectroscopy and liquid chromatography-based methods. We observed dysregulation of metabolic pathways including glutaminolysis, the citrate and urea cycles and glyoxylate detoxification. Constant, non-rhythmic glucocorticoid treatment rescued many of these changes, with some notable exceptions among the amino acid related pathways. Surprisingly, the non-rhythmic glucocorticoid treatment rescued almost half of the entire dysregulated diurnal transcriptome patterns. A combination of E-box and glucocorticoid response elements is enriched in the rescued genes. This simple enhancer element combination is sufficient to drive rhythmic circadian reporter gene expression under non-rhythmic glucocorticoid exposure, revealing a permissive function for the hormones in glucocorticoid-dependent circadian transcription. Our work highlights metabolic pathways potentially contributing to morbidity in patients with glucocorticoid deficiency, even under glucocorticoid replacement therapy. Moreover, we provide mechanistic insight into the interaction between the circadian clock and glucocorticoids in the transcriptional regulation of metabolism.

Nuclear Localised MORE SULPHUR ACCUMULATION1 Epigenetically Regulates Sulphur Homeostasis in Arabidopsis thaliana.

Sulphur (S) is an essential element for all living organisms. The uptake, assimilation and metabolism of S in plants are well studied. However, the regulation of S homeostasis remains largely unknown. Here, we report on the identification and characterisation of the more sulphur accumulation1 (msa1-1) mutant. The MSA1 protein is localized to the nucleus and is required for both S-adenosylmethionine (SAM) production and DNA methylation. Loss of function of the nuclear localised MSA1 leads to a reduction in SAM in roots and a strong S-deficiency response even at ample S supply, causing an over-accumulation of sulphate, sulphite, cysteine and glutathione. Supplementation with SAM suppresses this high S phenotype. Furthermore, mutation of MSA1 affects genome-wide DNA methylation, including the methylation of S-deficiency responsive genes. Elevated S accumulation in msa1-1 requires the increased expression of the sulphate transporter genes SULTR1;1 and SULTR1;2 which are also differentially methylated in msa1-1. Our results suggest a novel function for MSA1 in the nucleus in regulating SAM biosynthesis and maintaining S homeostasis epigenetically via DNA methylation.

The redox-sensitive module of cyclophilin 20-3, 2-cysteine peroxiredoxin and cysteine synthase integrates sulfur metabolism and oxylipin signaling in the high light acclimation response.

The integration of redox- and reactive oxygen species-dependent signaling and metabolic activities is fundamental to plant acclimation to biotic and abiotic stresses. Previous data suggest the existence of a dynamically interacting module in the chloroplast stroma consisting of cyclophilin 20-3 (Cyp20-3), O-acetylserine(thiol)lyase B (OASTL-B), 2-cysteine peroxiredoxins A/B (2-CysPrx) and serine acetyltransferase 2;1 (SERAT2;1). The functionality of this COPS module is influenced by redox stimuli and oxophytodienoic acid (OPDA), which is the precursor for jasmonic acid. The concept of an integrating function of these proteins in stress signaling was challenged by combining transcriptome and biochemical analyses in Arabidopsis mutants devoid of oastlB, serat2;1, cyp20-3 and 2-cysprxA/B, and wild-type (WT). Leaf transcriptomes were analyzed 6 h after transfer to light intensity 10-fold in excess of growth light or under growth light. The survey of KEGG-based gene ontology groups showed common upregulation of translation- and protein homeostasis-associated transcripts under control conditions in all mutants compared with WT. The results revealed that the interference of the module was accompanied with disturbance of carbohydrate, sulfur and nitrogen metabolism, and also citric acid cycle intermediates. Apart from common regulation, specific responses at the transcriptome and metabolite level linked Cyp20-3 to cell wall-bound carbohydrates and oxylipin signaling, and 2-CysPrx to photosynthesis, sugar and amino acid metabolism. Deletion of either OASTL-B or SERAT2;1 frequently induced antagonistic changes in biochemical or molecular features. Enhanced sensitivity of mutant seedlings to OPDA and leaf discs to NaHS-administration confirmed the presumed functional interference of the COPS module in redox and oxylipin signaling.

Drought-Enhanced Xylem Sap Sulfate Closes Stomata by Affecting ALMT12 and Guard Cell ABA Synthesis.

Water limitation of plants causes stomatal closure to prevent water loss by transpiration. For this purpose, progressing soil water deficit is communicated from roots to shoots. Abscisic acid (ABA) is the key signal in stress-induced stomatal closure, but ABA as an early xylem-delivered signal is still a matter of debate. In this study, poplar plants (Populus × canescens) were exposed to water stress to investigate xylem sap sulfate and ABA, stomatal conductance, and sulfate transporter (SULTR) expression. In addition, stomatal behavior and expression of ABA receptors, drought-responsive genes, transcription factors, and NCED3 were studied after feeding sulfate and ABA to detached poplar leaves and epidermal peels of Arabidopsis (Arabidopsis thaliana). The results show that increased xylem sap sulfate is achieved upon drought by reduced xylem unloading by PtaSULTR3;3a and PtaSULTR1;1, and by enhanced loading from parenchyma cells into the xylem via PtaALMT3b. Sulfate application caused stomatal closure in excised leaves and peeled epidermis. In the loss of sulfate-channel function mutant, Atalmt12, sulfate-triggered stomatal closure was impaired. The QUAC1/ALMT12 anion channel heterologous expressed in oocytes was gated open by extracellular sulfate. Sulfate up-regulated the expression of NCED3, a key step of ABA synthesis, in guard cells. In conclusion, xylem-derived sulfate seems to be a chemical signal of drought that induces stomatal closure via QUAC1/ALMT12 and/or guard cell ABA synthesis.