Biology subjects

Meyer, A. J.

Publications and source records attributed to Meyer, A. J..

At least 19 recordsLinked to original sources

bioRxiv2026

The SAUERKRAUT transposable element acceleratesArabidopsis floral transition

Salt stress alters plant development, including the floral transition, but regulation of timing of flowering by salt is poorly understood at the molecular level. To identify genetic loci regulating the floral transition under high soil salinity, we performed a genome-wide association study (GWAS) in Arabidopsis thaliana and identified natural variation at the UGT74E1-UGT74E2-BT3 (UUB) locus that correlates with bolting time specifically in response to salt stress. Genetic analysis revealed BT3 as a novel repressor of the floral transition in control conditions. Similarly, the putative IBA glycosylases UGT74E1 & UGT74E2 delay the floral transition in control conditions. Furthermore, we identified that IBA homeostasis regulators TOB1 and ECH2/IBR10 play a key role in the floral transition, and that ECH2/IBR10 are required for the early flowering phenotype of the ugt74e1/ugt74e2 double mutant, indicating that UGT74E1 & UGT74E2 delay flowering by altering IBA homeostasis. A pangenome analysis of the UUB locus revealed variation in the occurrence of the DNA transposon SAUERKRAUT (SKRT). CRISPR-mediated SKRT deletion in Col-0 affected gene expression both within and outside the UUB locus and caused a salt-dependent delayed floral transition. The delayed bolting phenotype of the skrt-2 mutant also depends on ECH2/IBR10 function, indicating that SKRT accelerates the floral transition by altering IBA homeostasis. Finally, targeted demethylation of SKRT resulted in delayed floral transition under salt stress. Taken together, our data show a role for SKRT and its DNA methylation levels in the salt-dependent bolting time response in Arabidopsis, revealing a novel molecular mechanism to control flowering in adverse conditions.

plant biology↗

bioRxiv2025

Root growth in Arabidopsis depends on the amount of glutathione and not the glutathione redox potential

Cell cycle activity and hence plant growth strictly depends on glutathione homeostasis. Despite compelling evidence for this dependency based on glutathione depletion, the cause for the cell cycle arrest had remained unclear. Cell cycle control may depend on either the absolute amount of glutathione or on the glutathione redox potential (EGSH). To unambiguously distinguish those two options, we characterized an allelic series of six Arabidopsis mutants affected in glutamate-cysteine ligase, which catalyses the first step for the biosynthesis of reduced glutathione (GSH). When grown under the same conditions, even mutants with 20% and 50% of wild-type GSH amounts are slightly stunted. The most severely compromised mutants, zir1 and rml1, were crossed with either gr1, which lacks cyto-nuclear glutathione disulfide reductase and was used to induce a pronounced shift in EGSH, or with bir6, which has a diminished glutathione consumption and thus exhibits slightly increased levels of GSH. Based on theoretical considerations, these levels are not expected to shift the EGSH to any significant extent. Our study shows that deleting GR1 in the zir1 or rml1 background does not result in an obvious phenotypic change. By contrast, deleting BIR6 was sufficient to suppress the growth arrest in rml1 and to attenuate the growth in zir1. These findings demonstrate that root growth is dependent on the availability of sufficient amounts of GSH, and not affected by pronounced changes in EGSH. This insight provides a decisive step towards understanding the mechanisms underpinning the proposed role of glutathione in cell cycle and growth control. HighlightCrosses of GSH-deficient Arabidopsis mutants with mutants affected in glutathione reduction or GSH consumption pinpoint the GSH amount rather than the glutathione redox potential as causative for changes in root growth.

plant biology↗

bioRxiv2025

Advanced illumination-imaging reveals photosynthesis-triggered pH, ATP and NAD redox signatures across plant cell compartments

Photosynthesis provides energy and organic substrates to most life. In plants, photosynthesis dominates chloroplast physiology but represents only a fraction of the tightly interconnected metabolic network that spans the entire cell. Here, we explore how photosynthetic activity affects energy physiology within and beyond the chloroplast. We developed a new standard for the live-monitoring of subcellular energy physiology by combining confocal imaging of genetically encoded fluorescent protein biosensors with advanced on-stage illumination technology to investigate pH, MgATP2- and NADH/NAD+ dynamics at dark-light transitions in Arabidopsis mesophyll cells. Our findings reveal a stromal alkalinization signature induced by photosynthetic proton pumping, extending to the cytosol and mitochondria as an alkalinization wave. Photosynthesis leads to increased MgATP2- levels in both the stroma and cytosol. Additionally, we observed reduction of the NAD pool driven by photosynthesis-derived electron export. Arabidopsis lines defective in chloroplast NADP- and mitochondrial NAD-dependent malate dehydrogenases show more reduced cytosolic NAD redox status even in darkness, highlighting the involvement of chloroplasts and mitochondria in shaping cytosolic redox metabolism via malate metabolism. Our study sets a novel methodological standard for precision live-monitoring of photosynthetic cell physiology. Applying this technology reveals signatures of photosynthetic physiology within and beyond the chloroplast with unprecedented resolution. Those signatures link photosynthetic activity and the fundamental biochemical functions of phototrophic cells. Significance statementBy applying novel live microscopy monitoring using fluorescent protein biosensors in plant cells, we reveal that dark-light transitions trigger profound re-orchestration of subcellular pH, ATP and NAD redox physiology not limited to chloroplasts but extending into the cytosol and the mitochondria.

plant biology↗

bioRxiv2025

The secreted redox sensor roGFP2-Orp1 reveals oxidative dynamics in the plant apoplast

- Specific generation of reactive oxygen species (ROS) is important for signalling and defence in many organisms. In plants, different types of ROS serve useful biological functions in the extracellular space (apoplast), influencing polymer structures as well as signaling during immune responses. The current knowledge of apoplastic ROS dynamics is limited, as dynamic monitoring of extracellular redox processes in vivo remains difficult. - We employed evolutionary distant land plant model species from bryophytes and flowering plants to test whether the genetically encoded redox biosensor roGFP2-Orp1 can be used to assess extracellular redox dynamics. - Secreted roGFP2-Orp1 can inform about local diffusion barriers and protein cysteinyl oxidation rate in the apoplast, after pre-reduction. Observed re-oxidation rates were slow, within the range of hours. Compared to Physcomitrium patens, re-oxidation in Arabidopsis thaliana was faster and increased after triggering an immune response. Comparing roGFP2-Orp1 signals in tip-growing P. patens protonema and Nicotiana tabacum pollen tubes, we consistently find no intracellular redox gradient, but partially reduced extracellular sensor in pollen tubes. - Our data indicate differences in extracellular oxidative processes between species and within a species, depending on cell type and immune signalling.

plant biology↗

bioRxiv2023

Abscisic acid signaling gates salt-specific responses of plant roots

Soil salinity presents a dual challenge for plants, involving both osmotic and ionic stress. In response, plants deploy distinct yet interconnected mechanisms to cope with these facets of salinity stress. In this investigation, we observed a substantial overlap in the salt (NaCl)-induced transcriptional responses of Arabidopsis roots with those triggered by osmotic stress or the plant stress hormone abscisic acid (ABA), as anticipated. Notably, a specific cluster of genes responded uniquely to sodium (Na+) ions. Surprisingly, expression of sodium-induced genes exhibited a negative correlation with the ABA response and preceded the activation of genes induced by the osmotic stress component of salt. Elevated exogenous ABA levels resulted in the complete abolition of sodium-induced responses. Consistently, ABA signalling mutants displayed prolonged sodium-induced gene expression, coupled with increased root cell damage under high salinity conditions. Moreover, ABA signalling mutants were unable to redirect root growth to avoid high sodium concentrations and failed to contain their root cell swelling in the presence of elevated salt levels. In summary, our findings unveil an unexpected and pivotal role for ABA signaling in mitigating cellular damage induced by salinity stress and modulating sodium-specific responses in plant roots.

plant biology↗

bioRxiv2023

Chloroplasts lacking class I glutaredoxins are functional but show a delayed recovery of protein cysteinyl redox state after oxidative challenge

Redox status of protein cysteinyl residues is mediated via glutathione (GSH)/glutaredoxin (GRX) and thioredoxin (TRX)-dependent redox cascades. An oxidative challenge can induce post-translational protein modifications on thiols, such as protein S-glutathionylation. Class I GRX are small thiol-disulfide oxidoreductases that reversibly catalyse S-glutathionylation and protein disulfide formation. TRX and GSH/GRX redox systems can provide partial backup for each other in several subcellular compartments, but not in the plastid stroma where TRX/light-dependent redox regulation of primary metabolism takes place. While the stromal TRX system has been studied at detail, the role of class I GRX on plastid redox processes in vivo is still unknown. We generate knockout lines of GRXC5 as the only chloroplast class I GRX of the moss Physcomitrium patens. While we find that class I PpGRXC5 has high activities in glutathione-dependent oxidoreductase assays using hydroxyethyl disulfide or redox-sensitive GFP2 (roGFP2) as substrates in vitro, {Delta}grxc5 plants show no detectable growth defect or stress sensitivity, in contrast to mutants with a less negative stromal EGSH ({Delta}gr1). Using stroma-targeted roGFP2, we show increased protein Cys oxidation and decreased reduction rates after oxidative challenge in {Delta}grxc5 plants in vivo, indicating kinetic uncoupling of the protein Cys redox state from glutathione redox potential. Protein Cys disulfide and S-glutathionylation formation rates after H2O2 treatment remained unchanged. Lack of class I GRX function in the stroma did not result in impaired carbon fixation. Our observations suggest specific roles for class I GRX in the efficient redox equilibration between EGSH and protein Cys in the plastid stroma as well as negligible cross-talk with metabolic regulation via the TRX system. We propose a model for stromal class I GRX function as efficient kinetic couplers of protein Cys redox state to the dynamic stromal EGSH and highlight the importance of identifying in vivo target proteins of GRXC5. One sentence summaryRemoval of class I GRX activity in the chloroplast stroma of P. patens kinetically uncouples GRX-dependent cysteine redox changes from the local glutathione redox potential, without an effect on NPQ or photosynthetic carbon reactions.

plant biology↗

bioRxiv2023

CYP79B2 and CYP79B3 contribute to root branching through production of the auxin precursor indole-3-acetonitrile

Lateral root placement, outgrowth and density are influenced by environmental changes, including salinity stress. CYP79B2 and B3 are two cytochrome P450 enzymes previously identified as required for root architecture remodeling in salt. They produce iAOx, a metabolite that can be converted into indole glucosinolates (IGs), camalexin and indole-3-acetic acid (IAA), a type of auxin. We report here that lateral root appearance, induced by an auxin maximum in the bending zone after gravistimulation, is delayed in the absence of CYP79B2/B3. This delay traces back to a decrease in early lateral root growth after emergence, taking place before lateral roots are macroscopically visible. We measured gene transcripts and abundance of metabolites in the iAOx pathway in root segments that are forming lateral roots. Genes involved in tryptophane and IG biosynthesis were upregulated in cyp79b2/b3 mutants, suggesting a transcriptional feedback-loop. Salt stress was found to increase the expression of genes involved in IAN biosynthesis, a precursor of both IAA and camalexin, in the root during lateral root formation. Moreover, salt increases the concentration of IAN in tissue forming lateral roots in a CYP79B2/B3 dependent manner, but these changes in IAN did not coincide with altered IAA levels. Both the reduction in lateral root density under salt and the delayed lateral root appearance in cyp79b2/b3 knock-out mutants can be complemented by exogenous application of IAN. Our results reveal a role for the iAOx pathway in regulating the timing of lateral root appearance, allowing the modulation of lateral root density under salt stress.

plant biology↗

bioRxiv2023

Localization of four class I glutaredoxins in the cytosol and the secretory pathway and characterization of their biochemical diversification

Class I glutaredoxins (GRXs) are catalytically active oxidoreductases and considered key proteins mediating reversible glutathionylation and deglutathionylation of protein thiols during development and stress responses. To narrow in on putative target proteins, it is mandatory to know the subcellular localization of the respective GRXs and to understand their catalytic activities and putative redundancy between isoforms in the same compartment. We show that GRXC1 and GRXC2 are cytosolic proteins with GRXC1 being attached to membranes through myristoylation. GRXC3 and GRXC4 are identified as type II membrane proteins along the early secretory pathway with their enzymatic function on the luminal side. Comparison of all four studied GRXs for their oxidoreductase function highlights biochemical diversification with GRXC1 and GRXC2 being better reductants than GRXC3 and GRXC4 with bis(2-hydroxyethyl) disulfide and oxidized roGFP2 as substrates. Vice versa, GRXC3 and GRXC4 are better oxidants of reduced roGFP2 in the reverse reaction. Analysis of electrostatic surface potentials mirrors the phylogenetic classification of class I GRXs but cannot fully account for the observed kinetic differences in their interaction with roGPF2. Despite localization of two class I GRXs each in the cytosol and the endomembrane system, the respective double null mutants are viable without obvious phenotypes. Summary statementWe identify Arabidopsis glutaredoxins GRXC3 and GRXC4 as type II membrane proteins in the secretory pathway and GRXC1 as attached to membranes through N-terminal myristoylation. Cytosolic GRXC1 and GRXC2 and luminal GRXC3 and GRXC4 display distinct biochemical properties in their redox activities.

plant biology↗

bioRxiv2023

Altered iron-sulfur cluster transfer in Arabidopsis mitochondria reveals lipoyl synthase as a Janus-faced enzyme that generates toxic sulfide

Iron-sulfur (Fe-S) cluster are vital cofactors in all domains of life. Mitochondrial Fe-S cluster assembly occurs in two major steps to first build [2Fe-2S] clusters and subsequently assemble these into [4Fe-4S] clusters. The two assembly machineries are interconnected by glutaredoxin S15 (GRXS15) that transfers [2Fe-2S] clusters to the second machinery. Diminished cluster transfer activity of GRXS15 in Arabidopsis mitochondria causes specific defects associated with lipoyl synthase (LIP1) activity. Conversely, overexpression of LIP1 in wild-type plants causes the release of toxic amounts of sulfide that can be detoxified by increasing the capacity for sulfide fixation through overexpression of O-acetylserine-(thiol)-lyase. The release of sulfide by lipoyl synthase causes a disturbance of mitochondrial sulfide homeostasis resulting in distinct and readily observable macroscopic phenotypes. These phenotypes enable a direct readout of consequences resulting from defects in Fe-S cluster assembly or targeted modulation of Fe-S cluster flux in mitochondria.

plant biology↗

bioRxiv2023

PLANT UNCOUPLING MITOCHONDRIAL PROTEIN 2 localizes to the Golgi

Mitochondria act as cellular hubs of energy transformation and metabolite conversion in most eukaryotes. Plant mitochondrial electron transport chains are particularly flexible, featuring alternative components, such as ALTERNATIVE NAD(P)H DEHYDROGENASES and ALTERNATIVE OXIDASES (AOXs), that can bypass proton translocation steps. PLANT UNCOUPLING MITOCHONDRIAL PROTEINS (named PUMPs or plant UCPs) have been identified in plants as homologues of mammalian Uncoupling Proteins (UCPs), and their biochemical and physiological roles have been investigated in the context of mitochondrial energy metabolism. To dissect UCP function in Arabidopsis, the two most conserved (UCP1 and UCP2) have been targeted in recent work by combining mutant lines to circumvent potential functional redundancy in vivo. Such approaches rely on the assumption that both proteins reside in the inner mitochondrial membrane as a prerequisite for functional redundancy. Yet, contradicting results have been reported on UCP2 localization in plants. Here we provide evidence that, conversely to UCP1, which is an abundant inner mitochondrial membrane protein, UCP2 localizes to the Golgi rather than to mitochondria. Based on multiple lines of new and prior evidence, we summarize the consensus view that we have reached and provide an example of how open, critical exchange within the research community is able to constructively address ambiguities. Our observations and considerations provide direction to the ongoing discussion about the functions of UCP proteins. They further offer new perspectives for the study of Golgi membrane transport and subcellular targeting principles of membrane proteins. Since 20 to 30 % of genes in plant genomes are predicted to encode transmembrane proteins and the function of most of those proteins has not been experimentally investigated, we highlight the importance of using independent evidence for localization as a prerequisite for understanding physiological function of membrane proteins.

plant biology↗

bioRxiv2023

Root branching in salt requires auxin-independent modulation of LBD16 function

Salinity stress constrains lateral root (LR) growth and severely impacts plant growth. Auxin signaling is indispensable for the regulation of LR formation. Nevertheless, the molecular mechanism of how salinity affects root auxin signaling and whether salt would steer alternative pathway(s) to regulate LR development is unknown. Here we show that the auxin-regulated transcription factor LATERAL ORGAN BOUNDARY DOMAIN (LBD)16, known as an essential player for LR development under control conditions, is regulated by an alternative non-canonical pathway under salinity. Salt represses auxin signaling but in parallel activates an upstream transcriptional activator of LBD16, ZINC FINGER OF ARABIDOPSIS THALIANA 6 (ZAT6). ZAT6 modulates the activity of LBD16 to contribute to downstream cell wall remodeling, and promotes LR development under salinity stress. Our study thus shows that root developmental plasticity in response to salt stress is achieved by integration of auxin-dependent repressive and salt-activated auxin-independent pathways converging on LBD16 to modulate root branching modulation under salinity.

plant biology↗

bioRxiv2022

High robustness of cytosolic glutathione redox potential under combined salt and osmotic stress in barley as revealed by the biosensor Grx1-roGFP2

O_LIBarley is a staple crop of major global importance and relatively resilient to a wide range of stress factors in the field. Transgenic reporter lines to investigate physiological parameters during stress treatments remain scarce. C_LIO_LIWe generated and characterized stable homozygous barley lines (cv. Golden Promise Fast) expressing the genetically-encoded biosensor Grx1-roGFP2, which indicates the redox potential of the major antioxidant glutathione in the cytosol. C_LIO_LIOur results demonstrate functionality of the sensor in living barley plants. We determined the glutathione redox potential (EGSH) of the cytosol to be in the range of -308 to -320 mV. EGSH was robust against a combined NaCl (150 mM) and water deficit treatment (-0.8 MPa) that caused growth retardation and showed only a minor oxidation after 96 h of treatment. C_LIO_LIWe conclude that the generated reporter lines are a novel resource to study stress resilience in barley. C_LI One sentence summaryGeneration and characterization of barley plants stably expressing Grx1-roGFP2 reveal high robustness of cytosolic glutathione redox potential (EGSH) under combined salt and osmotic stress.

plant biology↗

bioRxiv2020

Live monitoring of ROS-induced cytosolic redox changes with roGFP2-based sensors in plants

Plant cells produce reactive oxygen species (ROS) as by-products of oxygen metabolism and for signal transduction. Depending on their concentration and their site of production, ROS can cause oxidative damage within the cell, and must be effectively scavenged. Detoxification of the most stable ROS, hydrogen peroxide (H2O2), via the glutathione-ascorbate pathway may transiently alter the glutathione redox potential (EGSH). Changes in EGSH can thus be considered as a proxy of the oxidative load in the cell. Genetically encoded probes based on roGFP2 enable extended opportunities for in vivo monitoring of H2O2 and EGSH dynamics. Here, we report detailed protocols for live monitoring of both parameters in the cytosol with the probes Grx1-roGFP2 for EGSH and roGFP2-Orp1 for H2O2, respectively. The protocols have been adapted for live cell imaging with high lateral resolution on a confocal microscope and for multiparallel measurements in whole organs or intact seedlings in a fluorescence microplate reader. Elicitor-induced ROS generation is used as an example for illustration of the opportunities for dynamic ROS measurements that can easily be transferred to other scientific questions and model systems.

plant biology↗

bioRxiv2020

Chloroplast-derived photo-oxidative stress causes changes in H2O2 and EGSH in other subcellular compartments

Metabolic fluctuations in chloroplasts and mitochondria can trigger retrograde signals to modify nuclear gene expression. Mobile signals likely to be involved are reactive oxygen species (ROS), which can operate protein redox switches by oxidation of specific cysteine residues. Redox buffers such as the highly reduced glutathione pool serve as reservoirs of reducing power for several ROS scavenging and ROS-induced damage repair pathways. Formation of glutathione disulfide (GSSG) and a shift of the glutathione redox potential (EGSH) towards less negative values is considered a hallmark of several stress conditions. Here we used the herbicide methyl viologen (MV) to generate ROS locally in chloroplasts of intact Arabidopsis seedlings and recorded dynamic changes in EGSH and H2O2 levels with the genetically-encoded biosensors Grx1-roGFP2 (for EGSH) and roGFP2-Orp1 (for H2O2) targeted to chloroplasts, the cytosol or mitochondria. Treatment of seedlings with MV caused a rapid oxidation in chloroplasts and subsequently also in the cytosol and mitochondria. The MV-induced oxidation was significantly boosted by illumination with actinic light and largely abolished by inhibitors of photosynthetic electron transport. In addition, MV also induced an autonomous oxidation in the mitochondrial matrix in an electron transport chain activity-dependent manner that was milder than the oxidation triggered in chloroplasts by the combination of MV and light. In vivo redox biosensing resolves the spatiotemporal dynamics of compartmental responses to local ROS generation and provide a basis for understanding how compartment-specific redox dynamics may operate in retrograde signaling and stress acclimation in plants. One sentence summaryMethyl viologen-induced photooxidative stress causes an increase of H2O2 and oxidation of glutathione in chloroplasts, cytosol and mitochondria as well as autonomous oxidation in mitochondria.

plant biology↗

bioRxiv2020

GSTU7 affects growth performance and acts as an antagonist of oxidative stress induced by methyl viologen

Plant glutathione S-transferases (GSTs) are glutathione-dependent enzymes with versatile functions, mainly related to detoxification of electrophilic xenobiotics and peroxides. The Arabidopsis genome codes for 53 GSTs, divided into seven subclasses, however understanding of their precise functions is limited. A recent study showed that class II TGA transcription factors TGA2, TGA5 and TGA6 are essential for tolerance of UV-B-induced oxidative stress and that this tolerance is associated with an antioxidative function of cytosolic tau-class GSTUs. Specifically, TGA2 controls the expression of several GSTUs under UV-B light and constitutive expression of GSTU7 in the tga256 triple mutant is sufficient to revert the UV-B-susceptible phenotype of tga256. To further study the function of GSTU7, we characterized its role in mitigation of oxidative damage caused by the herbicide methyl viologen (MV). Under non-stress conditions, gstu7 null mutants were smaller than wild-type (WT) plants and delayed in the onset of the MV-induced antioxidative response, which led to accumulation of hydrogen peroxide and diminished seedling survival. Complementation of gstu7 by constitutively expressed GSTU7 rescued these phenotypes. Furthermore, live monitoring of the glutathione redox potential in intact cells with the fluorescent probe Grx1-roGFP2 revealed that GSTU7 overexpression completely abolished the MV-induced oxidation of the cytosolic glutathione buffer compared to WT plants. GSTU7 was found to act as a glutathione peroxidase able to complement the lack of peroxidase-type GSTs in yeast. Together, these findings show that GSTU7 is crucial in the antioxidative response by limiting oxidative damage and thus protecting cells from oxidative stress.

plant biology↗

bioRxiv2020

Branched-chain amino acid catabolism depends on GRXS15 through mitochondrial lipoyl cofactor homeostasis

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) has been shown to be involved in Fe-S cluster assembly in mitochondria of yeast and mammals. In plants, the role of the mitochondrial homologue GRXS15 has only partially been characterized. Arabidopsis grxs15 null mutants are not viable, but mutants complemented with the variant GRXS15 K83A develop with a dwarf phenotype. In an in-depth metabolic analysis, we show that most Fe-S cluster-dependent processes are not affected, including biotin biosynthesis, molybdenum cofactor biosynthesis and the electron transport chain. Instead, we observed an increase in most TCA cycle intermediates and amino acids, especially pyruvate, 2-oxoglutarate, glycine and branched-chain amino acids (BCAAs). The most pronounced accumulation occurred in branched-chain -keto acids (BCKAs), the first degradation products resulting from deamination of BCAAs. In wild-type plants, pyruvate, 2-oxoglutarate, glycine and BCKAs are all metabolized through decarboxylation by four mitochondrial lipoyl cofactor-dependent dehydrogenase complexes. Because these enzyme complexes are very abundant and the biosynthesis of the lipoyl cofactor depends on continuous Fe-S cluster supply to lipoyl synthase, this could explain why lipoyl cofactor-dependent processes are most sensitive to restricted Fe-S supply in GRXS15 K83A mutants. One-sentence summaryDeficiency in GRXS15 restricts protein lipoylation and causes metabolic defects in lipoyl cofactor-dependent dehydrogenase complexes, with branched-chain amino acid catabolism as dominant bottleneck.

plant biology↗

bioRxiv2019

Low-glutathione mutants are impaired in growth but do not show an increased sensitivity to moderate water deficit

Glutathione is considered a key metabolite for stress defense and elevated levels have frequently been proposed to positively influence stress tolerance. To investigate whether glutathione affects plant performance and the drought tolerance of plants, wild-type Arabidopsis plants and an allelic series of five mutants (rax1, pad2, cad2, nrc1, and zir1) with reduced glutathione contents between 21 and 63 % compared to wild-type glutathione content were phenotypically characterized for their shoot growth under control and water-limiting conditions using a shoot phenotyping platform. Under non-stress conditions the zir1 mutant with only 21 % glutathione showed a pronounced dwarf phenotype. All other mutants with intermediate glutathione contents up to 62 % in contrast showed consistently slightly smaller shoots than the wild-type. Moderate drought stress imposed through water withdrawal until shoot growth ceased showed that wild-type plants and all mutants responded similarly in terms of chlorophyll fluorescence and growth retardation. These results lead to the conclusion that glutathione is important for general plant performance but that the glutathione content does not affect tolerance to moderate drought conditions typically experienced by crops in the field.

plant biology↗

bioRxiv2019

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 re-activated to drive germination when the external conditions are favorable. Since the switchover from quiescence to re-activation 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-based (iodoTMT) thiol redox proteomics. The redox state across all Cys-peptides was shifted towards reduction from 27.1 % to 13.0 %. 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 cycle (TCA). 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.

plant biology↗