S1 basic leucine zipper transcription factors shape plant architecture by controlling C/N partitioning to apical and lateral organs

Plants tightly control growth of their lateral organs, which led to the concept of apical dominance. However, outgrowth of the dormant lateral primordia is sensitive to the plant's nutritional status, resulting in an immense plasticity in plant architecture. While the impact of hormonal regulation on apical dominance is well characterized, the prime importance of sugar signaling to unleash lateral organ formation has just recently emerged. Here, we aimed to identify transcriptional regulators, which control the trade-off between growth of apical versus lateral organs. Making use of locally inducible gain-of-function as well as single and higher-order loss-of-function approaches of the sugar-responsive S1-basic-leucine-zipper (S1-bZIP) transcription factors, we disclosed their largely redundant function in establishing apical growth dominance. Consistently, comprehensive phenotypical and analytical studies of S1-bZIP mutants show a clear shift of sugar and organic nitrogen (N) allocation from apical to lateral organs, coinciding with strong lateral organ outgrowth. Tissue-specific transcriptomics reveal specific clade III SWEET sugar transporters, crucial for long-distance sugar transport to apical sinks and the glutaminase GLUTAMINE AMIDO-TRANSFERASE 1_2.1, involved in N homeostasis, as direct S1-bZIP targets, linking the architectural and metabolic mutant phenotypes to downstream gene regulation. Based on these results, we propose that S1-bZIPs control carbohydrate (C) partitioning from source leaves to apical organs and tune systemic N supply to restrict lateral organ formation by C/N depletion. Knowledge of the underlying mechanisms controlling plant C/N partitioning is of pivotal importance for breeding strategies to generate plants with desired architectural and nutritional characteristics.

Natural variation of warm temperature-induced raffinose accumulation identifies TREHALOSE-6-PHOSPHATE SYNTHASE 1 as a modulator of thermotolerance

High-temperature stress limits plant growth and reproduction. Exposure to high temperature, however, also elicits a physiological response, which protects plants from the damage evoked by heat. This response involves a partial reconfiguration of the metabolome including the accumulation of the trisaccharide raffinose. In this study, we explored the intraspecific variation of warm temperature-induced raffinose accumulation as a metabolic marker for temperature responsiveness with the aim to identify genes that contribute to thermotolerance. By combining raffinose measurements in 250 Arabidopsis thaliana accessions following a mild heat treatment with genome-wide association studies, we identified five genomic regions that were associated with the observed trait variation. Subsequent functional analyses confirmed a causal relationship between TREHALOSE-6-PHOSPHATE SYNTHASE 1 (TPS1) and warm temperature-dependent raffinose synthesis. Moreover, complementation of the tps1-1 null mutant with functionally distinct TPS1 isoforms differentially affected carbohydrate metabolism under more severe heat stress. While higher TPS1 activity was associated with reduced endogenous sucrose levels and thermotolerance, disruption of trehalose 6-phosphate signalling resulted in higher accumulation of transitory starch and sucrose and was associated with enhanced heat resistance. Taken together, our findings suggest a role of trehalose 6-phosphate in thermotolerance, most likely through its regulatory function in carbon partitioning and sucrose homoeostasis.

The circadian clock is required for rhythmic lipid transport in Drosophila in interaction with diet and photic condition

Modern lifestyle is often at odds with endogenously driven rhythmicity, which can lead to circadian disruption and metabolic syndrome. One signature for circadian disruption is a reduced or altered metabolite cycling in the circulating tissue reflecting the current metabolic status. Drosophila is a well-established model in chronobiology, but day-time dependent variations of transport metabolites in the fly circulation are poorly characterized. Here, we sampled fly hemolymph throughout the day and analyzed diacylglycerols (DGs), phosphoethanolamines (PEs) and phosphocholines (PCs) using LC-MS. In wild-type flies kept on sugar-only medium under a light-dark cycle, all transport lipid species showed a synchronized bimodal oscillation pattern with maxima at the beginning and end of the light phase which were impaired in period01 clock mutants. In wild-type flies under constant dark conditions, the oscillation became monophasic with a maximum in the middle of the subjective day. In strong support of clock-driven oscillations, levels of the targeted lipids peaked once in the middle of the light phase under time-restricted feeding independent of the time of food intake. When wild-type flies were reared on full standard medium, the rhythmic alterations of hemolymph lipid levels were greatly attenuated. Our data suggest that the circadian clock aligns daily oscillations of DGs, PEs, and PCs in the hemolymph to the anabolic siesta phase, with a strong influence of light on phase and modality.

High triacylglycerol turnover is required for efficient opening of stomata during heat stress in Arabidopsis

Heat stress triggers the accumulation of triacylglycerols in Arabidopsis leaves, which increases basal thermotolerance. However, how triacylglycerol synthesis is linked to thermotolerance remains unclear and the mechanisms involved remain to be elucidated. It has been shown that triacylglycerol and starch degradation are required to provide energy for stomatal opening induced by blue light at dawn. To investigate whether triacylglycerol turnover is involved in heat-induced stomatal opening during the day, we performed feeding experiments with labeled fatty acids. Heat stress strongly induced both triacylglycerol synthesis and degradation to channel fatty acids destined for peroxisomal ß-oxidation through the triacylglycerol pool. Analysis of mutants defective in triacylglycerol synthesis or peroxisomal fatty acid uptake revealed that triacylglycerol turnover and fatty acid catabolism are required for heat-induced stomatal opening in illuminated leaves. We show that triacylglycerol turnover is continuous (1.2 mol% per min) in illuminated leaves even at 22°C. The ß-oxidation of triacylglycerol-derived fatty acids generates C₂ carbon units that are channeled into the tricarboxylic acid pathway in the light. In addition, carbohydrate catabolism is required to provide oxaloacetate as an acceptor for peroxisomal acetyl-CoA and maintain the tricarboxylic acid pathway for energy and amino acid production during the day.

Corrigendum: Honeybees are buffered against undernourishment during larval stages

[This corrects the article DOI: 10.3389/finsc.2022.951317.].

Honeybees are buffered against undernourishment during larval stages

The negative impact of juvenile undernourishment on adult behavior has been well reported for vertebrates, but relatively little is known about invertebrates. In honeybees, nutrition has long been known to affect task performance and timing of behavioral transitions. Whether and how a dietary restriction during larval development affects the task performance of adult honeybees is largely unknown. We raised honeybees in-vitro, varying the amount of a standardized diet (150 µl, 160 µl, 180 µl in total). Emerging adults were marked and inserted into established colonies. Behavioral performance of nurse bees and foragers was investigated and physiological factors known to be involved in the regulation of social organization were quantified. Surprisingly, adult honeybees raised under different feeding regimes did not differ in any of the behaviors observed. No differences were observed in physiological parameters apart from weight. Honeybees were lighter when undernourished (150 µl), while they were heavier under the overfed treatment (180 µl) compared to the control group raised under a normal diet (160 µl). These data suggest that dietary restrictions during larval development do not affect task performance or physiology in this social insect despite producing clear effects on adult weight. We speculate that possible effects of larval undernourishment might be compensated during the early period of adult life.

The major trimeric antenna complexes serve as a site for qH-energy dissipation in plants

Plants and algae are faced with a conundrum: harvesting sufficient light to drive their metabolic needs while dissipating light in excess to prevent photodamage, a process known as nonphotochemical quenching. A slowly relaxing form of energy dissipation, termed qH, is critical for plants’ survival under abiotic stress; however, qH location in the photosynthetic membrane is unresolved. Here, we tested whether we could isolate subcomplexes from plants in which qH was induced that would remain in an energy-dissipative state. Interestingly, we found that chlorophyll (Chl) fluorescence lifetimes were decreased by qH in isolated major trimeric antenna complexes, indicating that they serve as a site for qH-energy dissipation and providing a natively quenched complex with physiological relevance to natural conditions. Next, we monitored the changes in thylakoid pigment, protein, and lipid contents of antenna with active or inactive qH but did not detect any evident differences. Finally, we investigated whether specific subunits of the major antenna complexes were required for qH but found that qH was insensitive to trimer composition. Because we previously observed that qH can occur in the absence of specific xanthophylls, and no evident changes in pigments, proteins, or lipids were detected, we tentatively propose that the energy-dissipative state reported here may stem from Chl–Chl excitonic interaction.

Sphingolipid Long-Chain Base Phosphate Degradation Can Be a Rate-Limiting Step in Long-Chain Base Homeostasis

Sphingolipid long-chain bases (LCBs) are building blocks for membrane-localized sphingolipids, and are involved in signal transduction pathways in plants. Elevated LCB levels are associated with the induction of programmed cell death and pathogen-derived toxin-induced cell death. Therefore, levels of free LCBs can determine survival of plant cells. To elucidate the contribution of metabolic pathways regulating high LCB levels, we applied the deuterium-labeled LCB D-erythro-sphinganine-d7 (D₇-d18:0), the first LCB in sphingolipid biosynthesis, to Arabidopsis leaves and quantified labeled LCBs, LCB phosphates (LCB-Ps), and 14 abundant ceramide (Cer) species over time. We show that LCB D₇-d18:0 is rapidly converted into the LCBs d18:0P, t18:0, and t18:0P. Deuterium-labeled ceramides were less abundant, but increased over time, with the highest levels detected for Cer(d18:0/16:0), Cer(d18:0/24:0), Cer(t18:0/16:0), and Cer(t18:0/22:0). A more than 50-fold increase of LCB-P levels after leaf incubation in LCB D₇-d18:0 indicated that degradation of LCBs via LCB-Ps is important, and we hypothesized that LCB-P degradation could be a rate-limiting step to reduce high levels of LCBs. To functionally test this hypothesis, we constructed a transgenic line with dihydrosphingosine-1-phosphate lyase 1 (DPL1) under control of an inducible promotor. Higher expression of DPL1 significantly reduced elevated LCB-P and LCB levels induced by Fumonisin B₁, and rendered plants more resistant against this fungal toxin. Taken together, we provide quantitative data on the contribution of major enzymatic pathways to reduce high LCB levels, which can trigger cell death. Specifically, we provide functional evidence that DPL1 can be a rate-limiting step in regulating high LCB levels.

In Vitro Rearing Changes Social Task Performance and Physiology in Honeybees

Simple Summary

The rearing of honeybee larvae in the laboratory is an important tool for studying the effects of plant protection products or pathogens on developing and adult bees, yet how rearing under artificial conditions affects the later social behavior and physiology of the honeybees is mostly unknown. We, here, show that honeybees reared in the laboratory generally had a lower probability for performing nursing or foraging tasks compared to bees reared under natural conditions in bee colonies. Nursing behavior itself appeared normal in in vitro honeybees. In contrast, bees reared in the laboratory foraged for a shorter period in life and performed fewer trips compared to bees reared in colonies. In addition, in vitro honeybees did not display the typical increase in juvenile hormone titer, which goes hand-in-hand with the initiation of foraging in colony-reared bees.

Abstract

In vitro rearing of honeybee larvae is an established method that enables exact control and monitoring of developmental factors and allows controlled application of pesticides or pathogens. However, only a few studies have investigated how the rearing method itself affects the behavior of the resulting adult honeybees. We raised honeybees in vitro according to a standardized protocol: marking the emerging honeybees individually and inserting them into established colonies. Subsequently, we investigated the behavioral performance of nurse bees and foragers and quantified the physiological factors underlying the social organization. Adult honeybees raised in vitro differed from naturally reared honeybees in their probability of performing social tasks. Further, in vitro-reared bees foraged for a shorter duration in their life and performed fewer foraging trips. Nursing behavior appeared to be unaffected by rearing condition. Weight was also unaffected by rearing condition. Interestingly, juvenile hormone titers, which normally increase strongly around the time when a honeybee becomes a forager, were significantly lower in three- and four-week-old in vitro bees. The effects of the rearing environment on individual sucrose responsiveness and lipid levels were rather minor. These data suggest that larval rearing conditions can affect the task performance and physiology of adult bees despite equal weight, pointing to an important role of the colony environment for these factors. Our observations of behavior and metabolic pathways offer important novel insight into how the rearing environment affects adult honeybees.

Under salt stress guard cells rewire ion transport and abscisic acid signaling

Soil salinity is an increasingly global problem which hampers plant growth and crop yield. Plant productivity depends on optimal water-use efficiency and photosynthetic capacity balanced by stomatal conductance. Whether and how stomatal behavior contributes to salt sensitivity or tolerance is currently unknown. This work identifies guard cell-specific signaling networks exerted by a salt-sensitive and salt-tolerant plant under ionic and osmotic stress conditions accompanied by increasing NaCl loads. We challenged soil-grown Arabidopsis thaliana and Thellungiella salsuginea plants with short- and long-term salinity stress and monitored genome-wide gene expression and signals of guard cells that determine their function. Arabidopsis plants suffered from both salt regimes and showed reduced stomatal conductance while Thellungiella displayed no obvious stress symptoms. The salt-dependent gene expression changes of guard cells supported the ability of the halophyte to maintain high potassium to sodium ratios and to attenuate the abscisic acid (ABA) signaling pathway which the glycophyte kept activated despite fading ABA concentrations. Our study shows that salinity stress and even the different tolerances are manifested on a single cell level. Halophytic guard cells are less sensitive than glycophytic guard cells, providing opportunities to manipulate stomatal behavior and improve plant productivity.

Plant apocarotenoid metabolism utilizes defense mechanisms against reactive carbonyl species and xenobiotics

Carotenoid levels in plant tissues depend on the relative rates of synthesis and degradation of the molecules in the pathway. While plant carotenoid biosynthesis has been extensively characterized, research on carotenoid degradation and catabolism into apocarotenoids is a relatively novel field. To identify apocarotenoid metabolic processes, we characterized the transcriptome of transgenic Arabidopsis (Arabidopsis thaliana) roots accumulating high levels of β-carotene and, consequently, β-apocarotenoids. Transcriptome analysis revealed feedback regulation on carotenogenic gene transcripts suitable for reducing β-carotene levels, suggesting involvement of specific apocarotenoid signaling molecules originating directly from β-carotene degradation or after secondary enzymatic derivatizations. Enzymes implicated in apocarotenoid modification reactions overlapped with detoxification enzymes of xenobiotics and reactive carbonyl species (RCS), while metabolite analysis excluded lipid stress response, a potential secondary effect of carotenoid accumulation. In agreement with structural similarities between RCS and β-apocarotenoids, RCS detoxification enzymes also converted apocarotenoids derived from β-carotene and from xanthophylls into apocarotenols and apocarotenoic acids in vitro. Moreover, glycosylation and glutathionylation-related processes and translocators were induced. In view of similarities to mechanisms found in crocin biosynthesis and cellular deposition in saffron (Crocus sativus), our data suggest apocarotenoid metabolization, derivatization and compartmentalization as key processes in (apo)carotenoid metabolism in plants.

Optogenetic control of plant growth by a microbial rhodopsin

While rhodopsin-based optogenetics has revolutionized neuroscience1,2, poor expression of opsins and the absence of the essential cofactor all-trans-retinal has complicated the application of rhodopsins in plants. Here, we demonstrate retinal production in plants and improved rhodopsin targeting for green light manipulation of plant cells using the Guillardia theta light-gated anion channelrhodopsin GtACR13. Green light induces a massive increase in anion permeability and pronounced membrane potential changes when GtACR1 is expressed, enabling non-invasive manipulation of plant growth and leaf development. Using light-driven anion loss, we could mimic drought conditions and bring about leaf wilting despite sufficient water supply. Expressed in pollen tubes, global GtACR1 activation triggers membrane potential depolarizations due to large anion currents. While global illumination was associated with a reversible growth arrest, local GtACR1 activation at the flanks of the apical dome steers growth direction away from the side with increased anion conductance. These results suggest a crucial role of anion permeability for the guidance of pollen tube tip growth. This plant optogenetic approach could be expanded to create an entire pallet of rhodopsin-based tools4, greatly facilitating dissection of plant ion-signalling pathways.

Induction of Jasmonoyl-Isoleucine (JA-Ile)-Dependent JASMONATE ZIM-DOMAIN (JAZ) Genes in NaCl-Treated Arabidopsis thaliana Roots Can Occur at Very Low JA-Ile Levels and in the Absence of the JA/JA-Ile Transporter JAT1/AtABCG16

The plant hormone jasmonoyl-isoleucine (JA-Ile) is an important regulator of plant growth and defense in response to various biotic and abiotic stress cues. Under our experimental conditions, JA-Ile levels increased approximately seven-fold in NaCl-treated Arabidopsis thaliana roots. Although these levels were around 1000-fold lower than in wounded leaves, genes of the JA-Ile signaling pathway were induced by a factor of 100 or more. Induction was severely compromised in plants lacking the JA-Ile receptor CORONATINE INSENSITIVE 1 or enzymes required for JA-Ile biosynthesis. To explain efficient gene expression at very low JA-Ile levels, we hypothesized that salt-induced expression of the JA/JA-Ile transporter JAT1/AtABCG16 would lead to increased nuclear levels of JA-Ile. However, mutant plants with different jat1 alleles were similar to wild-type ones with respect to salt-induced gene expression. The mechanism that allows COI1-dependent gene expression at very low JA-Ile levels remains to be elucidated.

Alkaloid Concentrations of Lolium perenne Infected with Epichloë festucae var. lolii with Different Detection Methods-A Re-Evaluation of Intoxication Risk in Germany?

Mycotoxins in agriculturally used plants can cause intoxication in animals and can lead to severe financial losses for farmers. The endophytic fungus Epichloë festucae var. lolii living symbiotically within the cool season grass species Lolium perenne can produce vertebrate and invertebrate toxic alkaloids. Hence, an exact quantitation of alkaloid concentrations is essential to determine intoxication risk for animals. Many studies use different methods to detect alkaloid concentrations, which complicates the comparability. In this study, we showed that alkaloid concentrations of individual plants exceeded toxicity thresholds on real world grasslands in Germany, but not on the population level. Alkaloid concentrations on five German grasslands with high alkaloid levels peaked in summer but were also below toxicity thresholds on population level. Furthermore, we showed that alkaloid concentrations follow the same seasonal trend, regardless of whether plant fresh or dry weight was used, in the field and in a common garden study. However, alkaloid concentrations were around three times higher when detected with dry weight. Finally, we showed that alkaloid concentrations can additionally be biased to different alkaloid detection methods. We highlight that toxicity risks should be analyzed using plant dry weight, but concentration trends of fresh weight are reliable.

Hepatitis C Virus NS3 Protease and Helicase Inhibitors from Red Sea Sponge (Amphimedon) Species in Green Synthesized Silver Nanoparticles Assisted by in Silico Modeling and Metabolic Profiling

Background

Hepatitis C virus (HCV) infection is a major cause of hepatic diseases all over the world. This necessitates the need to discover novel anti-HCV drugs to overcome emerging drug resistance and liver complications.

Purpose

Total extract and petroleum ether fraction of the marine sponge (Amphimedon spp.) were used for silver nanoparticle (SNP) synthesis to explore their HCV NS3 helicase- and protease-inhibitory potential.

Methods

Characterization of the prepared SNPs was carried out with ultraviolet-visible spectroscopy, transmission electron microscopy, and Fourier-transform infrared spectroscopy. The metabolomic profile of different Amphimedon fractions was assessed using liquid chromatography coupled with high-resolution mass spectrometry. Fourteen known compounds were isolated and their HCV helicase and protease activities assessed using in silico modeling of their interaction with both HCV protease and helicase enzymes to reveal their anti-HCV mechanism of action. In vitro anti-HCV activity against HCV NS3 helicase and protease was then conducted to validate the computation results and compared to that of the SNPs.

Results

Transmission electron–microscopy analysis of NPs prepared from Amphimedon total extract and petroleum ether revealed particle sizes of 8.22–14.30 nm and 8.22–9.97 nm, and absorption bands at λ_max of 450 and 415 nm, respectively. Metabolomic profiling revealed the richness of Amphimedon spp. with different phytochemical classes. Bioassay-guided isolation resulted in the isolation of 14 known compounds with anti-HCV activity, initially revealed by docking studies. In vitro anti–HCV NS3 helicase and protease assays of both isolated compounds and NPs further confirmed the computational results.

Conclusion

Our findings indicate that Amphimedon, total extract, petroleum ether fraction, and derived NPs are promising biosources for providing anti-HCV drug candidates, with nakinadine B and 3,4-dihydro-6-hydroxymanzamine A the most potent anti-HCV agents, possessing good oral bioavailability and penetration power.

Epichloë Endophyte Infection rates and Alkaloid Content in Commercially Available Grass Seed Mixtures in Europe

Fungal endophytes of the genus Epichloë live symbiotically in cool season grass species and can produce alkaloids toxic to insects and vertebrates, yet reports of intoxication of grazing animals have been rare in Europe in contrast to overseas. However, due to the beneficial resistance traits observed in Epichloë infected grasses, the inclusion of Epichloë in seed mixtures might become increasingly advantageous. Despite the toxicity of fungal alkaloids, European seed mixtures are rarely tested for Epichloë infection and their infection status is unknown for consumers. In this study, we tested 24 commercially available seed mixtures for their infection rates with Epichloë endophytes and measured the concentrations of the alkaloids ergovaline, lolitrem B, paxilline, and peramine. We detected Epichloë infections in six seed mixtures, and four contained vertebrate and insect toxic alkaloids typical for Epichloë festucae var. lolii infecting Lolium perenne. As Epichloë infected seed mixtures can harm livestock, when infected grasses become dominant in the seeded grasslands, we recommend seed producers to test and communicate Epichloë infection status or avoiding Epichloë infected seed mixtures.

An improved growth medium for enhanced inoculum production of the plant growth-promoting fungus Serendipita indica

BACKGROUND

The plant endophytic fungus Serendipita indica colonizes roots of a wide range of plant species and can enhance growth and stress resistance of these plants. Due to its ease of axenic cultivation and its broad host plant range including the model plant Arabidopsis thaliana and numerous crop plants, it is widely used as a model fungus to study beneficial fungus-root interactions. In addition, it was suggested to be utilized for commercial applications, e.g. to enhance yield in barley and other species. To produce inoculum, S. indica is mostly cultivated in a complex Hill-Käfer medium (CM medium), however, growth in this medium is slow, and yield of chlamydospores, which are often used for plant root inoculation, is relatively low.

RESULTS

We tested and optimized a simple vegetable juice-based medium for an enhanced yield of fungal inoculum. The described vegetable juice (VJ) medium is based on commercially available vegetable juice and is easy to prepare. VJ medium was superior to the currently used CM medium with respect to biomass production in liquid medium and hyphal growth on agar plates. Using solid VJ medium supplemented with sucrose (VJS), a high amount of chlamydospores developed already after 8 days of cultivation, producing significantly more spores than on CM medium. Use of VJ medium is not restricted to S. indica, as it also supported growth of two pathogenic fungi often used in plant pathology experiments: the ascomycete Fusarium graminearum, the causal agent of Fusarium head blight disease on wheat and barley, and Verticillium longisporum, the causal agent of verticillium wilt.

CONCLUSIONS

The described VJ medium is recommended for streamlined and efficient production of inoculum for the plant endophytic fungus Serendipita indica and might prove superior for the propagation of other fungi for research purposes.

Chemical Priming by Isothiocyanates Protects Against Intoxication by Products of the Mustard Oil Bomb

In Brassicaceae, tissue damage triggers the mustard oil bomb i.e., activates the degradation of glucosinolates by myrosinases leading to a rapid accumulation of isothiocyanates at the site of damage. Isothiocyanates are reactive electrophilic species (RES) known to covalently bind to thiols in proteins and glutathione, a process that is not only toxic to herbivores and microbes but can also cause cell death of healthy plant tissues. Previously, it has been shown that subtoxic isothiocyanate concentrations can induce transcriptional reprogramming in intact plant cells. Glutathione depletion by RES leading to breakdown of the redox potential has been proposed as a central and common RES signal transduction mechanism. Using transcriptome analyses, we show that after exposure of Arabidopsis seedlings (grown in liquid culture) to subtoxic concentrations of sulforaphane hundreds of genes were regulated without depletion of the cellular glutathione pool. Heat shock genes were among the most highly up-regulated genes and this response was found to be dependent on the canonical heat shock factors A1 (HSFA1). HSFA1-deficient plants were more sensitive to isothiocyanates than wild type plants. Moreover, pretreatment of Arabidopsis seedlings with subtoxic concentrations of isothiocyanates increased resistance against exposure to toxic levels of isothiocyanates and, hence, may reduce the autotoxicity of the mustard oil bomb by inducing cell protection mechanisms.

Anti-Alzheimer potential, metabolomic profiling and molecular docking of green synthesized silver nanoparticles of Lampranthus coccineus and Malephora lutea aqueous extracts

The green synthesis of silver nanoparticles (SNPs) using plant extracts is an eco-friendly method. It is a single step and offers several advantages such as time reducing, cost-effective and environmental non-toxic. Silver nanoparticles are a type of Noble metal nanoparticles and it has tremendous applications in the field of diagnostics, therapeutics, antimicrobial activity, anticancer and neurodegenerative diseases. In the present work, the aqueous extracts of aerial parts of Lampranthus coccineus and Malephora lutea F. Aizoaceae were successfully used for the synthesis of silver nanoparticles. The formation of silver nanoparticles was early detected by a color change from pale yellow to reddish-brown color and was further confirmed by transmission electron microscope (TEM), UV-visible spectroscopy, Fourier transform infrared (FTIR) spectroscopy, dynamic light scattering (DLS), X-ray diffraction (XRD), and energy-dispersive X-ray diffraction (EDX). The TEM analysis of showed spherical nanoparticles with a mean size between 12.86 nm and 28.19 nm and the UV- visible spectroscopy showed λmax of 417 nm, which confirms the presence of nanoparticles. The neuroprotective potential of SNPs was evaluated by assessing the antioxidant and cholinesterase inhibitory activity. Metabolomic profiling was performed on methanolic extracts of L. coccineus and M. lutea and resulted in the identification of 12 compounds, then docking was performed to investigate the possible interaction between the identified compounds and human acetylcholinesterase, butyrylcholinesterase, and glutathione transferase receptor, which are associated with the progress of Alzheimer's disease. Overall our SNPs highlighted its promising potential in terms of anticholinesterase and antioxidant activity as plant-based anti-Alzheimer drug and against oxidative stress.

Metabolomic Profiling and Cytotoxic Tetrahydrofurofuran Lignans Investigations from Premna odorata Blanco

Metabolomic profiling of different Premna odorata Blanco (Lamiaceae) organs, bark, wood, young stems, flowers, and fruits dereplicated 20, 20, 10, 20, and 20 compounds, respectively, using LC–HRESIMS. The identified metabolites (1–34) belonged to different chemical classes, including iridoids, flavones, phenyl ethanoids, and lignans. A phytochemical investigation of P. odorata bark afforded one new tetrahydrofurofuran lignan, 4β-hydroxyasarinin 35, along with fourteen known compounds. The structure of the new compound was confirmed using extensive 1D and 2D NMR, and HRESIMS analyses. A cytotoxic investigation of compounds 35–38 against the HL-60, HT-29, and MCF-7 cancer cell lines, using the MTT assay showed that compound 35 had cytotoxic effects against HL-60 and MCF-7 with IC₅₀ values of 2.7 and 4.2 µg/mL, respectively. A pharmacophore map of compounds 35 showed two hydrogen bond acceptor (HBA) aligning the phenoxy oxygen atoms of benzodioxole moieties, two aromatic ring features vectored on the two phenyl rings, one hydrogen bond donor (HBD) feature aligning the central hydroxyl group and thirteen exclusion spheres which limit the boundaries of sterically inaccessible regions of the target’s active site.

Elevated Levels of Phosphorylated Sphingobases Do Not Antagonize Sphingobase- or Fumonisin B1-Induced Plant Cell Death

Long-chain bases (LCBs), also termed sphingobases, are building blocks of sphingolipids, which make up a significant proportion of the cellular membrane system. They are also bioactive molecules regulating intracellular processes. Elevated levels of LCBs like phytosphingosine and dihydrosphingosine can induce cell death in plants and correlate with programmed cell death (PCD) reactions after pathogen recognition. We investigated the previously hypothesized antagonism between phosphorylated and nonphosphorylated LCBs with respect to cell death in Arabidopsis thaliana. Using HPLC-MS/MS, we determined levels of phosphorylated and nonphosphorylated LCBs after cell death induction by LCB application or by Fumonisin B1 (FB1) treatment. We show that previously reported antagonistic effects of phosphorylated LCBs after simultaneous application with nonphosphorylated LCBs are linked to reduced uptake of nonphosphorylated LCBs into the tissue. Furthermore, phosphorylated LCBs did not antagonize PCD induced by avirulence protein recognition. In a functional approach, we used Arabidopsis lines with perturbed levels of phosphorylated LCBs. In these plants, the degree of FB1-induced cell death did not consistently correlate negatively with levels of phosphorylated LCBs, but positively with levels of major nonphosphorylated LCBs phytosphingosine and dihydrosphingosine. As treatment with phosphorylated LCBs did not antagonize cell death, and elevated in vivo levels of these LCB species did not reduce FB1-induced cell death, we conclude that the hypothesized general cell death-antagonizing effect of phosphorylated LCBs in plant cell death reactions should be rejected. Instead, our time-course analysis of LCB levels during cell death reactions showed a positive correlation between levels of nonphosphorylated LCBs and cell death.

Metabolomic profiling and anti-infective potential of Zinnia elegans and Gazania rigens (Family Asteraceae)

The present study evaluates the chemical composition of Zinnia elegans and Gazania rigens based on their metabolomic profiles using liquid chromatography coupled with high-resolution mass spectrometry (LC-HR-MS), alongside with the anti-infective activities of their ethanol extracts, as well as, different fractions. A significant difference was observed between the LC-MS profiles of the two plants such as, coumarins, sesquiterpene lactones and phenylethanoids which were characteristic for Z. elegans, while amides and phenolic acid derivatives were characteristic for G. rigens. These results highlight the chemical potential of Z. elegans and G. rigens. Furthermore, the ethyl acetate fraction of Z. elegans showed a significant antimalarial activity with IC₅₀ values of 21.03 and 13.72 µg/mL against Plasmodium falciparum D₆ and P. falciparum W₂, respectively.

Hepatoprotective potential of Malvaviscus arboreus against carbon tetrachloride-induced liver injury in rats

Malvaviscus arboreus Cav. is a medicinal plant belonging to family Malvaceae with both ethnomedical and culinary value; however, its phytochemical and biological profiles have been scarcely studied. Accordingly, this work was designed to explore the chemical composition and the hepatoprotective potential of M. arboreus against carbon tetrachloride (CCl4)-induced hepatotoxicity. The total extract of the aerial parts and its derived fractions (petroleum ether, dichloromethane, ethyl acetate, and aqueous) were orally administered to rats for six consecutive days, followed by injection of CCl4 (1:1 v/v, in olive oil, 1.5 ml/kg, i.p.) on the next day. Results showed that the ethyl acetate and dichloromethane fractions significantly alleviated liver injury in rats as indicated by the reduced levels of alanine transaminase (ALT), aspartate transaminase (AST), alkaline phosphatase (ALP), total bilirubin (TB), and malondialdehyde (MDA), along with enhancement of the total antioxidant capacities of their livers, with the maximum effects were recorded by the ethyl acetate fraction. Moreover, the protective actions of both fractions were comparable to those of silymarin (100 mg/kg), and have been also substantiated by histopathological evaluations. On the other hand, liquid chromatography-high resolution electrospray ionization mass spectrometry (LC‒HR‒ESI‒MS) metabolomic profiling of the crude extract of M. arboreus aerial parts showed the presence of a variety of phytochemicals, mostly phenolics, whereas the detailed chemical analysis of the most active fraction (i.e. ethyl acetate) resulted in the isolation and identification of six compounds for the first time in the genus, comprising four phenolic acids; β-resorcylic, caffeic, protocatechuic, and 4-hydroxyphenylacetic acids, in addition to two flavonoids; trifolin and astragalin. Such phenolic principles, together with their probable synergistic antioxidant and liver-protecting properties, seem to contribute to the observed hepatoprotective potential of M. arboreus.

TGA2 signaling in response to reactive electrophile species is not dependent on cysteine modification of TGA2

Reactive electrophile species (RES), including prostaglandins, phytoprostanes and 12-oxo phytodienoic acid (OPDA), activate detoxification responses in plants and animals. However, the pathways leading to the activation of defense reactions related to abiotic or biotic stress as a function of RES formation, accumulation or treatment are poorly understood in plants. Here, the thiol-modification of proteins, including the RES-activated basic region/leucine zipper transcription factor TGA2, was studied. TGA2 contains a single cysteine residue (Cys186) that was covalently modified by reactive cyclopentenones but not required for induction of detoxification genes in response to OPDA or prostaglandin A1. Activation of the glutathione-S-transferase 6 (GST6) promoter was responsive to cyclopentenones but not to unreactive cyclopentanones, including jasmonic acid suggesting that thiol reactivity of RES is important to activate the TGA2-dependent signaling pathway resulting in GST6 activation We show that RES modify thiols in numerous proteins in vivo, however, thiol reactivity alone appears not to be sufficient for biological activity as demonstrated by the failure of several membrane permeable thiol reactive reagents to activate the GST6 promoter.

Phospholipid:Diacylglycerol Acyltransferase-Mediated Triacylglyerol Synthesis Augments Basal Thermotolerance

High temperatures rapidly induce a genetically programmed heat-shock response (HSR) that is essential to establish short-term acquired thermotolerance. In addition, an immediate HSR-independent metabolic response is triggered, resulting in an accumulation of unsaturated triacylglycerols (TAGs) in the cytosol. The metabolic processes involved in heat-induced TAG formation in plants and their physiological significance remain to be clarified. Lipidomic analyses of Arabidopsis (Arabidopsis thaliana) seedlings indicated that during heat stress, polyunsaturated fatty acids from thylakoid galactolipids are incorporated into cytosolic TAGs. In addition, rapid conversion of plastidic monogalactosyl diacylglycerols (MGDGs) into oligogalactolipids, acylated MGDGs, and diacylglycerols (DAGs), the direct precursor of TAGs, was observed. For TAG synthesis, DAG requires a fatty acid from the acyl-CoA pool or phosphatidylcholine. Since seedlings deficient in PHOSPHOLIPID:DIACYLGLYCEROL ACYLTRANSFERASE1 (PDAT1) were unable to accumulate TAGs after heat stress, phosphatidylcholine appears to be the major fatty acid donor. Results suggest that rapid plastid lipid metabolism drives TAG accumulation during heat stress. PDAT1-mediated TAG accumulation was found to increase heat resistance, since nonacclimated pdat1 mutant seedlings were more sensitive to severe heat stress, as indicated by a more dramatic decline of the maximum efficiency of PSII and lower seedling survival compared to wild-type seedlings. In contrast, nonacclimated trigalactosyldiacylglycerol1 (tgd1) mutants overaccumulating TAGs and oligogalactolipids were more resistant to heat stress. Hence, thylakoid lipid metabolism and TAG formation increases thermotolerance in addition to the genetically encoded HSR.

Enzymatic and Non-Enzymatic Mechanisms Contribute to Lipid Oxidation During Seed Aging

Storage of seeds is accompanied by loss of germination and oxidation of storage and membrane lipids. A lipidomic analysis revealed that during natural and artificial aging of Arabidopsis seeds, levels of several diacylglycerols and free fatty acids, such as linoleic acid and linolenic acid as well as free oxidized fatty acids and oxygenated triacylglycerols, increased. Lipids can be oxidized by enzymatic or non-enzymatic processes. In the enzymatic pathway, lipoxygenases (LOXs) catalyze the first oxygenation step of polyunsaturated fatty acids. Analysis of lipid levels in mutants with defects in the two 9-LOX genes revealed that the strong increase in free 9-hydroxy- and 9-keto-fatty acids is dependent on LOX1 but not LOX5. Fatty acid oxidation correlated with an aging-induced decrease of germination, raising the question of whether these oxylipins negatively regulate germination. However, seeds of the lox1 mutant were only slightly more tolerant to aging, indicating that 9-LOX products contribute to but are not the major cause of loss of germination during aging. In contrast to free oxidized fatty acids, accumulation of oxygenated triacylglycerols upon accelerated aging was mainly based on non-enzymatic oxidation of seed storage lipids.

Enhanced aphid abundance in spring desynchronizes predator-prey and plant-microorganism interactions

Climate change leads to phenology shifts of many species. However, not all species shift in parallel, which can desynchronize interspecific interactions. Within trophic cascades, herbivores can be top-down controlled by predators or bottom-up controlled by host plant quality and host symbionts, such as plant-associated micro-organisms. Synchronization of trophic levels is required to prevent insect herbivore (pest) outbreaks. In a common garden experiment, we simulated an earlier arrival time (~2 weeks) of the aphid Rhopalosiphum padi on its host grass Lolium perenne by enhancing the aphid abundance during the colonization period. L. perenne was either uninfected or infected with the endophytic fungus Epichloë festucae var. lolii. The plant symbiotic fungus produces insect deterring alkaloids within the host grass. Throughout the season, we tested the effects of enhanced aphid abundance in spring on aphid predators (top-down) and grass-endophyte (bottom-up) responses. Higher aphid population sizes earlier in the season lead to overall higher aphid abundances, as predator occurrence was independent of aphid abundances on the pots. Nonetheless, after predator occurrence, aphids were controlled within 2 weeks on all pots. Possible bottom-up control of aphids by increased endophyte concentrations occurred time delayed after high herbivore abundances. Endophyte-derived alkaloid concentrations were not significantly affected by enhanced aphid abundance but increased throughout the season. We conclude that phenology shifts in an herbivorous species can desynchronize predator-prey and plant-microorganism interactions and might enhance the probability of pest outbreaks with climate change.

Reactive electrophilic oxylipins trigger a heat stress-like response through HSFA1 transcription factors

Abiotic and biotic stresses are often characterized by an induction of reactive electrophile species (RES) such as the jasmonate 12-oxo-phytodienoic acid (OPDA) or the structurally related phytoprostanes. Previously, RES oxylipins have been shown massively to induce heat-shock-response (HSR) genes including HSP101 chaperones. Moreover, jasmonates have been reported to play a role in basal thermotolerance. We show that representative HSR marker genes are strongly induced by RES oxylipins through the four master regulator transcription factors HSFA1a, b, d, and e essential for short-term adaptation to heat stress in Arabidopsis. When compared with Arabidopsis seedlings treated at the optimal acclimation temperature of 37 °C, the exogenous application of RES oxylipins at 20 °C induced a much weaker induction of HSP101 at both the gene and protein expression levels which, however, was not sufficient to confer short-term acquired thermotolerance. Moreover, jasmonate-deficient mutant lines displayed a wild-type-like HSR and were not compromised in acquiring thermotolerance. Hence, the OPDA- and RES oxylipin-induced HSR is not sufficient to protect seedlings from severe heat stress but may help plants to cope better with stresses associated with protein unfolding by inducing a battery of chaperones in the absence of heat.

Characterization of the Arabidopsis thaliana 2-Cys peroxiredoxin interactome

Peroxiredoxins are ubiquitous thiol-dependent peroxidases for which chaperone and signaling roles have been reported in various types of organisms in recent years. In plants, the peroxidase function of the two typical plastidial 2-Cys peroxiredoxins (2-Cys PRX A and B) has been highlighted while the other functions, particularly in ROS-dependent signaling pathways, are still elusive notably due to the lack of knowledge of interacting partners. Using an ex vivo approach based on co-immunoprecipitation of leaf extracts from Arabidopsis thaliana wild-type and mutant plants lacking 2-Cys PRX expression followed by mass spectrometry-based proteomics, 158 proteins were found associated with 2-Cys PRXs. Already known partners like thioredoxin-related electron donors (Chloroplastic Drought-induced Stress Protein of 32kDa, Atypical Cysteine Histidine-rich Thioredoxin 2) and enzymes involved in chlorophyll synthesis (Protochlorophyllide OxidoReductase B) or carbon metabolism (Fructose-1,6-BisPhosphatase) were identified, validating the relevance of the approach. Bioinformatic and bibliographic analyses allowed the functional classification of the identified proteins and revealed that more than 40% are localized in plastids. The possible roles of plant 2-Cys PRXs in redox signaling pathways are discussed in relation with the functions of the potential partners notably those involved in redox homeostasis, carbon and amino acid metabolisms as well as chlorophyll biosynthesis.

An essential developmental function for murine phosphoglycolate phosphatase in safeguarding cell proliferation

Mammalian phosphoglycolate phosphatase (PGP) is thought to target phosphoglycolate, a 2-deoxyribose fragment derived from the repair of oxidative DNA lesions. However, the physiological role of this activity and the biological function of the DNA damage product phosphoglycolate is unknown. We now show that knockin replacement of murine Pgp with its phosphatase-inactive Pgp^D34N mutant is embryonically lethal due to intrauterine growth arrest and developmental delay in midgestation. PGP inactivation attenuated triosephosphate isomerase activity, increased triglyceride levels at the expense of the cellular phosphatidylcholine content, and inhibited cell proliferation. These effects were prevented under hypoxic conditions or by blocking phosphoglycolate release from damaged DNA. Thus, PGP is essential to sustain cell proliferation in the presence of oxygen. Collectively, our findings reveal a previously unknown mechanism coupling a DNA damage repair product to the control of intermediary metabolism and cell proliferation.

Staphylococcus aureus Exploits a Non-ribosomal Cyclic Dipeptide to Modulate Survival within Epithelial Cells and Phagocytes

Community-acquired (CA) Staphylococcus aureus cause various diseases even in healthy individuals. Enhanced virulence of CA-strains is partly attributed to increased production of toxins such as phenol-soluble modulins (PSM). The pathogen is internalized efficiently by mammalian host cells and intracellular S. aureus has recently been shown to contribute to disease. Upon internalization, cytotoxic S. aureus strains can disrupt phagosomal membranes and kill host cells in a PSM-dependent manner. However, PSM are not sufficient for these processes. Here we screened for factors required for intracellular S. aureus virulence. We infected escape reporter host cells with strains from an established transposon mutant library and detected phagosomal escape rates using automated microscopy. We thereby, among other factors, identified a non-ribosomal peptide synthetase (NRPS) to be required for efficient phagosomal escape and intracellular survival of S. aureus as well as induction of host cell death. By genetic complementation as well as supplementation with the synthetic NRPS product, the cyclic dipeptide phevalin, wild-type phenotypes were restored. We further demonstrate that the NRPS is contributing to virulence in a mouse pneumonia model. Together, our data illustrate a hitherto unrecognized function of the S. aureus NRPS and its dipeptide product during S. aureus infection.

Screen Identifying Arabidopsis Transcription Factors Involved in the Response to 9-Lipoxygenase-Derived Oxylipins

13-Lipoxygenase-derived oxylipins, such as jasmonates act as potent signaling molecules in plants. Although experimental evidence supports the impact of oxylipins generated by the 9-Lipoxygenase (9-LOX) pathway in root development and pathogen defense, their signaling function in plants remains largely elusive. Based on the root growth inhibiting properties of the 9-LOX-oxylipin 9-HOT (9-hydroxy-10,12,15-octadecatrienoic acid), we established a screening approach aiming at identifying transcription factors (TFs) involved in signaling and/or metabolism of this oxylipin. Making use of the AtTORF-Ex (ArabidopsisthalianaTranscription Factor Open Reading Frame Expression) collection of plant lines overexpressing TF genes, we screened for those TFs which restore root growth on 9-HOT. Out of 6,000 lines, eight TFs were recovered at least three times and were therefore selected for detailed analysis. Overexpression of the basic leucine Zipper (bZIP) TF TGA5 and its target, the monoxygenase CYP81D11 reduced the effect of added 9-HOT, presumably due to activation of a detoxification pathway. The highly related ETHYLENE RESPONSE FACTORs ERF106 and ERF107 induce a broad detoxification response towards 9-LOX-oxylipins and xenobiotic compounds. From a set of 18 related group S-bZIP factors isolated in the screen, bZIP11 is known to participate in auxin-mediated root growth and may connect oxylipins to root meristem function. The TF candidates isolated in this screen provide starting points for further attempts to dissect putative signaling pathways involving 9-LOX-derived oxylipins.

Accumulation of extra-chloroplastic triacylglycerols in Arabidopsis seedlings during heat acclimation

Heat acclimation enables plants to tolerate and survive short-term heat stress on hot days. In Arabidopsis thaliana, a genetically programmed heat shock response can be rapidly triggered in the temperature range of 32-38°C through activation of heat shock transcription factors (HSF). The heat shock response leads to heat acclimation and confers short-term protection against temperatures above 40°C. However, little is known about metabolic adjustments during heat acclimation.Untargeted metabolite analyses of A. thaliana seedlings revealed that levels of polyunsaturated triacylglycerols (TG) rapidly and dramatically increase during heat acclimation. TG accumulation was found to be temperature dependent in a temperature range of 32-50°C (optimum at 42°C) and reversible after a return from 37°C to normal growth temperatures. Heat-induced TGs accumulated in extra-chloroplastic compartments and increased in both roots and shoots to a similar extent. Analysis of mutants deficient in all four HSFA1 master regulator genes or the HSFA2 gene revealed that TG accumulation was not dependent on HSFs. Moreover, the TG response was not limited to heat stress because drought and salt stress also triggered an accumulation of TGs, but not short-term osmotic, cold, and high light stress. Lipid analysis revealed that heat-induced accumulation of TGs was not due to massive de novo fatty acid synthesis. It is hypothesized that TGs serve as transient stores for fatty acids that may be required for membrane remodelling during heat acclimation.

Crosstalk between Two bZIP Signaling Pathways Orchestrates Salt-Induced Metabolic Reprogramming in Arabidopsis Roots

Soil salinity increasingly causes crop losses worldwide. Although roots are the primary targets of salt stress, the signaling networks that facilitate metabolic reprogramming to induce stress tolerance are less understood than those in leaves. Here, a combination of transcriptomic and metabolic approaches was performed in salt-treated Arabidopsis thaliana roots, which revealed that the group S1 basic leucine zipper transcription factors bZIP1 and bZIP53 reprogram primary C- and N-metabolism. In particular, gluconeogenesis and amino acid catabolism are affected by these transcription factors. Importantly, bZIP1 expression reflects cellular stress and energy status in roots. In addition to the well-described abiotic stress response pathway initiated by the hormone abscisic acid (ABA) and executed by SnRK2 (Snf1-RELATED-PROTEIN-KINASE2) and AREB-like bZIP factors, we identify a structurally related ABA-independent signaling module consisting of SnRK1s and S1 bZIPs. Crosstalk between these signaling pathways recruits particular bZIP factor combinations to establish at least four distinct gene expression patterns. Understanding this signaling network provides a framework for securing future crop productivity.

Profiling a gut microbiota-generated catechin metabolite's fate in human blood cells using a metabolomic approach

The microbial catechin metabolite δ-(3,4-dihydroxy-phenyl)-γ-valerolactone (M1) has been found in human plasma samples after intake of maritime pine bark extract (Pycnogenol). M1 has been previously shown to accumulate in endothelial and blood cells in vitro after facilitated uptake and to exhibit anti-inflammatory activity. The purpose of the present research approach was to systematically and comprehensively analyze the metabolism of M1 in human blood cells in vitro and in vivo. A metabolomic approach that had been successfully applied for drug metabolite profiling was chosen to detect 19 metabolite peaks of M1 which were subsequently further analyzed and validated. The metabolites were categorized into three levels of identification according to the Metabolomics Standards Initiative with six compounds each confirmed at levels 1 and 2 and seven putative metabolites at level 3. The predominant metabolites were glutathione conjugates which were rapidly formed and revealed prolonged presence within the cells. Although a formation of an intracellular conjugate of M1 and glutathione (M1-GSH) was already known two GSH conjugate isomers, M1-S-GSH and M1-N-GSH were observed in the current study. Additionally detected organosulfur metabolites were conjugates with oxidized glutathione and cysteine. Other biotransformation products constituted the open-chained ester form of M1 and a methylated M1. Six of the metabolites determined in in vitro assays were also detected in blood cells in vivo after ingestion of the pine bark extract by two volunteers. The present study provides the first evidence that multiple and structurally heterogeneous polyphenol metabolites can be generated in human blood cells. The bioactivity of the M1 metabolites and their contribution to the previously determined anti-inflammatory effects of M1 now need to be elucidated.

2-cysteine peroxiredoxins and thylakoid ascorbate peroxidase create a water-water cycle that is essential to protect the photosynthetic apparatus under high light stress conditions

Different peroxidases, including 2-cysteine (2-Cys) peroxiredoxins (PRXs) and thylakoid ascorbate peroxidase (tAPX), have been proposed to be involved in the water-water cycle (WWC) and hydrogen peroxide (H2O2)-mediated signaling in plastids. We generated an Arabidopsis (Arabidopsis thaliana) double-mutant line deficient in the two plastid 2-Cys PRXs (2-Cys PRX A and B, 2cpa 2cpb) and a triple mutant deficient in 2-Cys PRXs and tAPX (2cpa 2cpb tapx). In contrast to wild-type and tapx single-knockout plants, 2cpa 2cpb double-knockout plants showed an impairment of photosynthetic efficiency and became photobleached under high light (HL) growth conditions. In addition, double-mutant plants also generated elevated levels of superoxide anion radicals, H2O2, and carbonylated proteins but lacked anthocyanin accumulation under HL stress conditions. Under HL conditions, 2-Cys PRXs seem to be essential in maintaining the WWC, whereas tAPX is dispensable. By comparison, this HL-sensitive phenotype was more severe in 2cpa 2cpb tapx triple-mutant plants, indicating that tAPX partially compensates for the loss of functional 2-Cys PRXs by mutation or inactivation by overoxidation. In response to HL, H2O2- and photooxidative stress-responsive marker genes were found to be dramatically up-regulated in 2cpa 2cpb tapx but not 2cpa 2cpb mutant plants, suggesting that HL-induced plastid to nucleus retrograde photooxidative stress signaling takes place after loss or inactivation of the WWC enzymes 2-Cys PRX A, 2-Cys PRX B, and tAPX.

Lipid-Pro: a computational lipid identification solution for untargeted lipidomics on data-independent acquisition tandem mass spectrometry platforms

A major challenge for mass spectrometric-based lipidomics, aiming at describing all lipid species in a biological sample, lies in the computational and bioinformatic processing of the large amount of data that arises after data acquisition. Lipid-Pro is a software tool that supports the identification of lipids by interpreting large datasets generated by liquid chromatography--tandem mass spectrometry (LC-MS/MS) using the advanced data-independent acquisition mode MS(E). In the MS(E) mode, the instrument fragments all molecular ions generated from a sample and records time-resolved molecular ion data as well as fragment ion data for every detectable molecular ion. Lipid-Pro matches the retention time-aligned mass-to-charge ratio data of molecular- and fragment ions with a lipid database and generates a report on all identified lipid species. For generation of the lipid database, Lipid-Pro provides a module for construction of lipid species and their fragments using a flexible building block approach. Hence, Lipid-Pro is an easy to use analysis tool to interpret complex MS(E) lipidomics data and also offers a module to generate a user-specific lipid database.

AVAILABILITY AND IMPLEMENTATION

Lipid-Pro is freely available at: http://www.neurogenetics.biozentrum.uni-wuerzburg.de/en/project/services/lipidpro/.

SUPPLEMENTARY INFORMATION

Supplementary data are available at Bioinformatics online.

Upper extremity impairments, pain and disability in patients with diabetes mellitus

OBJECTIVES

To determine the severity of, and relationships between, upper extremity impairments, pain and disability in patients with diabetes mellitus, and to compare upper extremity impairments in patients with diabetes with non-diabetic controls.

DESIGN

Case-control, cross-sectional design.

SETTING

University-based, outpatient diabetes centre and physical therapy research clinic.

PARTICIPANTS

Two hundred and thirty-six patients with diabetes attending an outpatient diabetes clinic completed the Shoulder Pain and Disability Index (SPADI) questionnaire. A detailed shoulder and hand examination was conducted on a subgroup of 29 volunteers with type 2 diabetes, and 27 controls matched for age, sex and body mass index.

INTERVENTIONS

None.

MAIN OUTCOME MEASURES

SPADI score, passive shoulder range of motion (ROM) and strength, grip strength, hand sensation, dexterity and limited joint mobility of the hand.

RESULTS

Sixty-three percent (149/236) of patients with diabetes reported shoulder pain and/or disability [median SPADI score 10.0 (interquartile range 0.0 to 39.6)]. Compared with the control group, the subgroup of patients with diabetes had substantial reductions in shoulder ROM, shoulder muscle strength, grip and key pinch strength (P<0.05). Patients with diabetes had a greater prevalence of decreased sensation (26/27 vs 14/27) and limited joint mobility of the hand (17/27 vs 4/27) compared with the control group. Total SPADI score was negatively correlated (P<0.05) with shoulder ROM (r=-0.42 to -0.74) and strength measures (r=-0.44 to -0.63) in patients with diabetes.

CONCLUSIONS

Upper extremity impairments in this sample of patients with diabetes were common, severe and related to complaints of pain and disability. Additional research is needed to understand the unique reasons for upper extremity problems in patients with diabetes, and to identify preventative treatments.

Peramine and lolitrem B from endophyte-grass associations cascade up the food chain

Endophytic fungi in cool-season grass species produce herbivore-toxic alkaloids, which are assumed to harm higher trophic levels along food chains. Previous studies have shown fitness disadvantages for higher trophic levels that feed on aphids that were exclusively reared on perennial ryegrass (Lolium perenne) infected with the endophytic fungus Neotyphodium lolii. However, it is unknown whether the alkaloids produced by the fungus-grass association can be assimilated by plant sap-sucking insects like aphids. Using an ultra high performance liquid chromatography method combined with mass spectrometry, we provide the first evidence that the alkaloids peramine and lolitrem B are present in aphids (Rhopalosiphum padi) and in aphid predators when the aphids are reared on endophyte-infected grass. We conclude that alkaloids can enter the plant sap of the grass and are responsible for longer pupal stages of the ladybird Harmonia axyridis and for fitness disadvantages of aphids and their predators as shown in previous studies.

Kinetics of retrograde signalling initiation in the high light response of Arabidopsis thaliana

High light acclimation depends on retrograde control of nuclear gene expression. Retrograde regulation uses multiple signalling pathways and thus exploits signal patterns. To maximally challenge the acclimation system, Arabidopsis thaliana plants were either adapted to 8 (low light (L-light)) or 80 µmol quanta m(-2) s(-1) (normal light (N-light)) and subsequently exposed to a 100- and 10-fold light intensity increase, respectively, to high light (H-light, 800 µmol quanta m(-2) s(-1)), for up to 6 h. Both L → H- and N → H-light plants efficiently regulated CO2 assimilation to a constant level without apparent damage and inhibition. This experimental set-up was scrutinized for time-dependent regulation and efficiency of adjustment. Transcriptome profiles revealed that N-light and L-light plants differentially accumulated 2119 transcripts. After 6 h in H-light, only 205 remained differently regulated between the L → H- and N → H-light plants, indicating efficient regulation allowing the plants to reach a similar transcriptome state. Time-dependent analysis of transcripts as markers for signalling pathways, and of metabolites and hormones as possibly involved transmitters, suggests that oxylipins such as oxophytodienoic acid and jasmonic acid, metabolites and redox cues predominantly control the acclimation response, whereas abscisic acid, salicylic acid and auxins play an insignificant or minor role.

Two fatty acid desaturases, STEAROYL-ACYL CARRIER PROTEIN Δ9-DESATURASE6 and FATTY ACID DESATURASE3, are involved in drought and hypoxia stress signaling in Arabidopsis crown galls

Agrobacterium tumefaciens-derived crown galls of Arabidopsis (Arabidopsis thaliana) contain elevated levels of unsaturated fatty acids and strongly express two fatty acid desaturase genes, ω3 FATTY ACID DESATURASE3 (FAD3) and STEAROYL-ACYL CARRIER PROTEIN Δ9-DESATURASE6 (SAD6). The fad3-2 mutant with impaired α-linolenic acid synthesis developed significantly smaller crown galls under normal, but not under high, relative humidity. This strongly suggests that FAD3 plays a role in increasing drought stress tolerance of crown galls. SAD6 is a member of the SAD family of as yet unknown function. Expression of the SAD6 gene is limited to hypoxia, a physiological condition found in crown galls. As no sad6 mutant exists and to link the function of SAD6 with fatty acid desaturation in crown galls, the lipid pattern was analyzed of plants with constitutive SAD6 overexpression (SAD6-OE). SAD6-OE plants contained lower stearic acid and higher oleic acid levels, which upon reduction of SAD6 overexpression by RNA interference (SAD6-OE-RNAi) regained wild-type-like levels. The development of crown galls was not affected either in SAD6-OE or SAD6-OE-RNAi or by RNA interference in crown galls. Since biochemical analysis of SAD6 in yeast (Saccharomyces cerevisiae) and Escherichia coli failed, SAD6 was ectopically expressed in the background of the well-known suppressor of salicylic acid-insensitive2 (ssi2-2) mutant to confirm the desaturase function of SAD6. All known ssi2-2 phenotypes were rescued, including the high stearic acid level. Thus, our findings suggest that SAD6 functions as a Δ9-desaturase, and together with FAD3 it increases the levels of unsaturated fatty acids in crown galls under hypoxia and drought stress conditions.

Manipulation of methyl jasmonate esterase activity renders tomato more susceptible to Sclerotinia sclerotiorum

Jasmonic acid methyl ester has been discussed as a stress signal in plants. To investigate the relevance of reversible methylation of jasmonic acid, stress responses of transgenic tomato lines with altered expression and activity of methyl jasmonate esterase were analysed. No consistent changes in levels of methyl jasmonate, 12-oxo-phytodienoic acid, jasmonic acid, jasmonic acid isoleucine and expression of the jasmonate-responsive genes AOC and PINII between control line and RNAi as well as overexpressing lines were detectable under basal and wound-induced conditions. In contrast, reduction as well as enhancement of methyl jasmonate esterase activity resulted in increased susceptibility to the fungal pathogen Sclerotinia sclerotiorum despite higher levels of the hormonal active jasmonic acid isoleucine conjugate. Results suggest that methyl jasmonate esterase has a function in vivo in plant defence, which appears not to be related to its in vitro capacity to hydrolyse methyl jasmonate.

Arabidopsis lipocalins AtCHL and AtTIL have distinct but overlapping functions essential for lipid protection and seed longevity

Lipocalins are a group of multifunctional proteins, recognized as carriers of small lipophilic molecules, which have been characterized in bacteria and animals. Two true lipocalins have been recently identified in plants, the temperature-induced lipocalin (TIL) and the chloroplastic lipocalin (CHL), the expression of which is induced by various abiotic stresses. Each lipocalin appeared to be specialized in the responses to specific stress conditions in Arabidopsis thaliana, with AtTIL and AtCHL playing a protective role against heat and high light, respectively. The double mutant AtCHL KO × AtTIL KO deficient in both lipocalins was more sensitive to temperature, drought and light stresses than the single mutants, exhibiting intense lipid peroxidation. AtCHL deficiency dramatically enhanced the photosensitivity of mutants (vte1, npq1) affected in lipid protection mechanisms (tocopherols, zeaxanthin), confirming the role of lipocalins in the prevention of lipid peroxidation. Seeds of the AtCHL KO × AtTIL KO double mutant were very sensitive to natural and artificial ageing, and again this phenomenon was associated with the oxidation of polyunsaturated lipids. The presented results show that the Arabidopsis lipocalins AtTIL and AtCHL have overlapping functions in lipid protection which are essential for stress resistance and survival.

A tandem affinity purification tag of TGA2 for isolation of interacting proteins in Arabidopsis thaliana

Tandem affinity purification (TAP) tagging provides a powerful tool for isolating interacting proteins in vivo. TAP-tag purification offers particular advantages for the identification of stimulus-induced protein interactions. Type II bZIP transcription factors (TGA2, TGA5 and TGA6) play key roles in pathways that control salicylic acid, ethylene, xenobiotic and reactive oxylipin signaling. Although proteins interacting with these transcription factors have been identified through genetic and yeast 2-hybrid screening, others are still elusive. We have therefore generated a C-terminal TAP-tag of TGA2 to isolate additional proteins that interact with this transcription factor. Three lines most highly expressing TAP-tagged TGA2 were functional in that they partially complemented reactive oxylipin-responsive gene expression in a tga2 tga5 tga6 triple mutant. TAP-tagged TGA2 in the most strongly overexpressing line was proteolytically less stable than in the other 2 lines. Only this overexpressing line could be used in a 2-step purification process, resulting in isolation of co-purifying bands of larger molecular weight than TGA2. TAP-tagged TGA2 was used to pull down NPR1, a protein known to interact with this transcription factor. Mass spectrometry was used to identify peptides that co-purified with TAP-tagged TGA2. Having generated this TGA2 TAP-tag line will therefore be an asset to researchers interested in stimulus-induced signal transduction processes.

Structural basis for the recognition of mycolic acid precursors by KasA, a condensing enzyme and drug target from Mycobacterium tuberculosis

The survival of Mycobacterium tuberculosis depends on mycolic acids, very long α-alkyl-β-hydroxy fatty acids comprising 60-90 carbon atoms. However, despite considerable efforts, little is known about how enzymes involved in mycolic acid biosynthesis recognize and bind their hydrophobic fatty acyl substrates. The condensing enzyme KasA is pivotal for the synthesis of very long (C38-42) fatty acids, the precursors of mycolic acids. To probe the mechanism of substrate and inhibitor recognition by KasA, we determined the structure of this protein in complex with a mycobacterial phospholipid and with several thiolactomycin derivatives that were designed as substrate analogs. Our structures provide consecutive snapshots along the reaction coordinate for the enzyme-catalyzed reaction and support an induced fit mechanism in which a wide cavity is established through the concerted opening of three gatekeeping residues and several α-helices. The stepwise characterization of the binding process provides mechanistic insights into the induced fit recognition in this system and serves as an excellent foundation for the development of high affinity KasA inhibitors.