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

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

HYPK controls stability and catalytic activity of the N-terminal acetyltransferase A in Arabidopsis thaliana.

The ribosome-tethered N-terminal acetyltransferase A (NatA) acetylates 52% of soluble proteins in Arabidopsis thaliana. This co-translational modification of the N terminus stabilizes diverse cytosolic plant proteins. The evolutionary conserved Huntingtin yeast partner K (HYPK) facilitates NatA activity in planta, but in vitro, its N-terminal helix α1 inhibits human NatA activity. To dissect the regulatory function of HYPK protein domains in vivo, we genetically engineer CRISPR-Cas9 mutants expressing a HYPK fragment lacking all functional domains (hypk-cr1) or an internally deleted HYPK variant truncating helix α1 but retaining the C-terminal ubiquitin-associated (UBA) domain (hypk-cr2). We find that the UBA domain of HYPK is vital for stabilizing the NatA complex in an organ-specific manner. The N terminus of HYPK, including helix α1, is critical for promoting NatA activity on substrates starting with various amino acids. Consequently, deleting only 42 amino acids inside the HYPK N terminus causes substantial destabilization of the plant proteome and higher tolerance toward drought stress.

Assessment of the relevance of midwifery competencies in academic education in Germany from the midwives' perspective: A structural analysis of cross-sectional survey data.

INTRODUCTION: The acquisition of academic competencies is one of the main outcomes of the academization of midwifery education. To analyze midwives' views on the key academic competencies of the recently reformed midwifery education in Germany, an existing assessment instrument was adapted to the German context of care and psychometrically analyzed. Furthermore, it was investigated whether the relevance assessments of academic and non-academic midwives differ from each other. METHODS: The study design was cross-sectional. A total of 193 (prospective) midwives answered the items on the assessed relevance of midwifery competencies in academic education (59 items); 3 items were added (referring to evidence-based practice and digital literacy). Construct validity was tested using exploratory factor analysis. Item and reliability analysis as well as unpaired t-tests were performed. RESULTS: Considering insufficient item-construct associations (20 items), a single factorial solution best fits the data (eigenvalue: 18.36; explained variance: 29.60%). Internal reliability was demonstrated to be very good with Cronbach's α=0.954. The assessed relevance of academic midwifery competencies from academic and non-academic midwives did not differ significantly from each other for students and trainee midwives (t=0.18; df=6.66; p=0.86), and for for midwives educated at vocational school and university (t= -0.035; df=106; p=0.97). CONCLUSIONS: The adapted assessment tool can be used with minor modifications to reliably and validly measure the assessed relevance of academic competence from the midwives' perspective. Combined with data on the assessments of medical practitioners and laypersons, the assessment provides a substantial data basis for the development of a competence profile for academic midwifery education in Germany.

Nt-acetylation-independent turnover of SQUALENE EPOXIDASE 1 by Arabidopsis DOA10-like E3 ligases.

The acetylation-dependent (Ac/)N-degron pathway degrades proteins through recognition of their acetylated N-termini (Nt) by E3 ligases called Ac/N-recognins. To date, specific Ac/N-recognins have not been defined in plants. Here we used molecular, genetic, and multiomics approaches to characterize potential roles for Arabidopsis (Arabidopsis thaliana) DEGRADATION OF ALPHA2 10 (DOA10)-like E3 ligases in the Nt-acetylation-(NTA)-dependent turnover of proteins at global- and protein-specific scales. Arabidopsis has two endoplasmic reticulum (ER)-localized DOA10-like proteins. AtDOA10A, but not the Brassicaceae-specific AtDOA10B, can compensate for loss of yeast (Saccharomyces cerevisiae) ScDOA10 function. Transcriptome and Nt-acetylome profiling of an Atdoa10a/b RNAi mutant revealed no obvious differences in the global NTA profile compared to wild type, suggesting that AtDOA10s do not regulate the bulk turnover of NTA substrates. Using protein steady-state and cycloheximide-chase degradation assays in yeast and Arabidopsis, we showed that turnover of ER-localized SQUALENE EPOXIDASE 1 (AtSQE1), a critical sterol biosynthesis enzyme, is mediated by AtDOA10s. Degradation of AtSQE1 in planta did not depend on NTA, but Nt-acetyltransferases indirectly impacted its turnover in yeast, indicating kingdom-specific differences in NTA and cellular proteostasis. Our work suggests that, in contrast to yeast and mammals, targeting of Nt-acetylated proteins is not a major function of DOA10-like E3 ligases in Arabidopsis and provides further insight into plant ERAD and the conservation of regulatory mechanisms controlling sterol biosynthesis in eukaryotes.

Assessment of interprofessional obstetric and midwifery care from the midwives' perspective using the Interprofessional Collaboration Scale (ICS).

Introduction: Interprofessional collaboration of physicians and midwives is essential for appropriate and safe care of pregnant and parturient women as well as their newborns. The complexity of woman-centered care settings requires the continuous exchange of information and the coordinated implementation of multi-and interprofessional care concepts. To analyze the midwives' perspective on the multi-and interprofessional care process during pregnancy, birth and postpartum period, we aimed to adapt and psychometrically evaluate the Interprofessional Collaboration Scale (ICS). Methods: The ICS (13 items) was answered by 299 midwives for (i) prenatal and postpartum care as well as (ii) perinatal care. Three items on equitable communication (EC) identified in qualitative interviews with N = 6 midwives were added as further aspects of quality in collaborative midwifery care. Confirmatory factor analysis was used to test competing theoretically hypothesized factorial model structures, including both care settings simultaneously, i.e., birth and prenatal/postpartum. Results: A two-dimensional structure assuming the 13 original ICS items and the 3 items on EC as psychometric distinct item groups accounts for the data best. After deleting 5 ICS items with insufficient indicator reliability, a very good-fitting model structure was obtained for both prenatal/postpartum as well as perinatal care: χ2df = 192 = 226.35, p = 0.045, CFI = 0.991, RMSEA = 0.025 (90%CI: [0.004; 0.037]). Both the reduced ICS-R and the EC scale (standardized response mean = 0.579/1.401) indicate significantly higher interprofessional collaboration in the birth setting. Responsibility in consulting, attitudes toward obstetric care and frequency of collaboration with other professional groups proved to be associated with the ICS-R and EC scale as expected. Discussion: For the adapted ICS-R and the EC scale a good construct validity could be confirmed. Thus, the scales can be recommended as a promising assessment for recording the collaboration of midwives with physicians working in obstetric care from the perspective of midwives. The instrument provides a validated assessment basis in midwifery and obstetric care to identify potentially divergent perspectives within interprofessional care teams in woman's centered care.

Dynamic association of the plastid localized cysteine synthase complex is vital for efficient cysteine production, photosynthesis, and granal thylakoid formation in transgenic tobacco.

Cysteine biosynthesis is essential for translation and represents the entry point of reduced sulfur into plant metabolism. The two consecutively acting enzymes serine acetyltransferase (SAT) and O-acetylserine-thiol-lyase catalyse cysteine production and form the cysteine synthase complex, in which SAT is activated. Here we show that tobacco (Nicotiana tabacum) expressing active SAT in plastids (referred to as PSA lines) shows substantial cysteine accumulation in plastids. Remarkably, enhanced cysteine production in plastids entirely abolished granal stack formation, impaired photosynthesis capacity, and decreased the number of chloroplasts in mesophyll cells of the PSA lines. A transgenic tobacco line expressing active SAT in the cytosol accumulated comparable amounts of thiols but displayed no phenotype. To dissect the consequences of cysteine synthase complex formation from enhanced SAT activity in tobacco plastids, we expressed an enzymatically inactive SAT that can still form the cysteine synthase complex in tobacco plastids (PSI lines). The PSI lines were indistinguishable from the PSA lines, although the PSI lines displayed no increase in plastid-localized SAT activity. Neither PSA lines nor PSI lines suffered from an oxidized redox environment in plastids that could have been causative for the disturbed photosynthesis. From these findings, we infer that the association of the plastid cysteine synthase complex itself triggers a signaling cascade controlling sulfur assimilation and photosynthetic capacity in leaves.

Intentional and actional components of engaged participation in public health research studies: qualitative synthesis of a recruitment and retention process into the theory-informed INTACT-RS framework.

BACKGROUND: Ensuring motivated and successful study participation is a key challenge in the design and conduct of health research studies. Previously, recruitment barriers and facilitators have been identified mainly from experience, and rarely based on theoretical approaches. We developed a framework of intentional and actional components of engaged participation in public health research studies (INTACT-RS), informed by psychological behavioral models. We aimed a) to identify precise indicators for each framework component and b) to better understand which components and decision processes are essential for study participants. METHODS: Within a multicenter research network, we applied various approaches to recruit parents of newborns, pediatricians, and midwives. All recruitment processes were documented from the perspective of both participants and researchers. We used different qualitative and quantitative data material, which we applied in a multistage process according to the basic principles of qualitative content analysis. RESULTS: INTACT-RS encompasses pre-intentional, intentional and actional phases with a total of n = 15 components covering all aspects of an individual's involvement with a research study. During intention formation, an understanding of efforts and benefits, why participation is valuable beyond contributing to research, and how others perceive the study, were particularly important to (potential) participants. Subsequently (intentional phase), participants consider how and when participation is compatible with their own resources, ability and availability, and hence seek for close communication with, and flexibility and support from the research team. During and after (initial) participation (actional phase), participants' assessment of whether expectations and interests have been met impact crucial further steps, especially the willingness to continue and to recommend participation to others. A strong topic-wise and or supportive participation interest as well as active, continuous exchange with the researchers appeared to be central determinants of study completion and data validity. CONCLUSIONS: A theoretical framework is now available to plan and conduct recruitment of different target groups, which accounts for essential motivational and volitional decision-making processes. Based on empirically specified constructs, possible barriers can be addressed even before the initial recruitment process. Therefore, recommendations for scientific practice have been formulated.

Relative Protein Lifetime Measurement in Plants Using Tandem Fluorescent Protein Timers.

Targeted protein degradation plays a wide range of important roles in plant growth and development, but analyzing protein turnover in vivo is technically challenging. Until recently, there has been no straightforward methodology for quantifying protein dynamics at subcellular resolution during cellular transitions in plants. A tandem fluorescent protein timer (tFT) is a fusion of two different fluorescent proteins with distinct fluorophore maturation kinetics, which allows estimation of relative protein age from the ratio of fluorescence intensities of the two fluorescent proteins. Here, we describe approaches to use this technology to report relative protein lifetime in both transient and stable plant transformation systems. tFTs enable in vivo, real-time protein lifetime assessment within subcellular compartments and across tissues, permitting the analysis of protein degradation dynamics in response to stresses or developmental cues and in different genetic backgrounds.

Mitochondrial alternative NADH dehydrogenases NDA1 and NDA2 promote survival of reoxygenation stress in Arabidopsis by safeguarding photosynthesis and limiting ROS generation.

Plant submergence stress is a growing problem for global agriculture. During desubmergence, rising O2 concentrations meet a highly reduced mitochondrial electron transport chain (mETC) in the cells. This combination favors the generation of reactive oxygen species (ROS) by the mitochondria, which at excess can cause damage. The cellular mechanisms underpinning the management of reoxygenation stress are not fully understood. We investigated the role of alternative NADH dehydrogenases (NDs), as components of the alternative mETC in Arabidopsis, in anoxia-reoxygenation stress management. Simultaneous loss of the matrix-facing NDs, NDA1 and NDA2, decreased seedling survival after reoxygenation, while overexpression increased survival. The absence of NDAs led to reduced maximum potential quantum efficiency of photosystem II linking the alternative mETC to photosynthetic function in the chloroplast. NDA1 and NDA2 were induced upon reoxygenation, and transcriptional activation of NDA1 was controlled by the transcription factors ANAC016 and ANAC017 that bind to the mitochondrial dysfunction motif (MDM) in the NDA1 promoter. The absence of NDA1 and NDA2 did not alter recovery of cytosolic ATP levels and NADH : NAD+ ratio at reoxygenation. Rather, the absence of NDAs led to elevated ROS production, while their overexpression limited ROS. Our observations indicate that the control of ROS formation by the alternative mETC is important for photosynthetic recovery and for seedling survival of anoxia-reoxygenation stress.

Burden of informal caregivers of people without natural speech: a mixed-methods intervention study.

BACKGROUND: People with disabilities and without natural speech often rely on care provided by informal caregivers. The caregiving situation of these informal caregivers has been poorly researched. The objectives of the study are 1) to identify stressors, resources, and coping strategies among informal caregivers of people without natural speech and 2) to examine whether a complex intervention in augmentative and alternative communication (AAC) that is not primarily tailored to the needs of informal caregivers can reduce care-related burden. METHODS: The main components of the AAC intervention were (1) initial counselling session, (2) 4 AAC training sessions, (3) 20 AAC therapy sessions and (4) accompanying case management. The control group received only the initial counselling session. Within a quasi-experimental intervention study, survey data on self-perceived burden (Burden Scale for Family Caregivers, BSFC-s) from n = 154 informal caregivers of people without natural speech were collected at three time points between June 2018 and April 2021 from a postal survey. Qualitative interviews with n = 16 informal caregivers were conducted. RESULTS: Caregivers reported various stressors such as limited communication with the cared-for person and concerns about the living situation in adulthood. Diverse resources and effective coping strategies, which the caregivers refer to when dealing with stressors, could also be identified. Burden was significantly reduced in the intervention group compared to the control group. According to the results of the qualitative study, AAC use led to better communication skills and a reduction in behavioural problems and thus a decreased burden. CONCLUSIONS: The AAC intervention seems to have a positive impact on self-perceived burden. Linkages between intervention components and burden reduction as well as stressors and coping strategies could be identified and provide an evidence-based foundation for developing future holistic interventions for families with individuals without natural speech. TRIAL REGISTRATION: German Clinical Trials Register (DRKS); ID: DRKS00013628 (registered on 05/02/2018).

Why context matters when changing the diet: A narrative review of placebo, nocebo, and psychosocial context effects and implications for outcome research and nutrition counselling.

Placebo (PE) and nocebo effects (NE) have been subjects of systematic research in medicine and psychotherapy for many decades to distinguish between the (specific) pharmacological effect of medication and the (unspecific) effect of the context. Despite this significant research, the awareness, operationalisation, and reflection of the multiplicity of PE, NE, and psychosocial context effects (PSCE) is currently limited when researching outcomes of diet changes in studies without randomisation and placebo control. This neglection is critical as it could systematically influence outcomes by moderating and mediating them and thus reducing the validity and evidence base of these studies. Therefore, we performed a (non-systematic) narrative review (NR) on the following objectives: (1) present a concise overview about the relevance of PE, NE, and PSCE in medicine and nutrition research; (2) review the current state of research on reflecting context effects when studying diet changes; (3) provide useful theoretical foundations via consideration and integration of micro- and macro context effects; (4) operationalise as hypotheses the potential PE, NE, and PSCE which are specific for researching diet changes; and (5) derive their impact for future research as well as for nutrition counselling. The electronic search in this NR for objective (2) identified N = 5 publications and for objective (4) we found N = 61 articles retrieved in the first round of search, additional references were identified by a manual and snowball search among the cited references resulting finally in N = 37. This NR offers a synoptical basis to foster awareness and operationalisation of a variety of PE, NE, and PSCE. Interdisciplinary research teams should monitor these factors using, e.g., qualitative, mixed-method studies, process evaluation, item bank approaches, moderator and mediator analysis that might reveal substantially new insights, and outcomes of relevance to science and nutrition counselling. Nevertheless, the present NR has several limitations, especially as it is non-systematic, because it is a very heterogeneous field of research, in which the topic we are investigating is usually regarded as marginal and subordinate. Therefore, future research should conduct systematic reviews and particularly theory-based primary studies (experimental research) on hypotheses of PE, NE, and PSCE in outcome research in diet changes.

From Nucleus to Membrane: A Subcellular Map of the N-Acetylation Machinery in Plants.

N-terminal acetylation (NTA) is an ancient protein modification conserved throughout all domains of life. N-terminally acetylated proteins are present in the cytosol, the nucleus, the plastids, mitochondria and the plasma membrane of plants. The frequency of NTA differs greatly between these subcellular compartments. While up to 80% of cytosolic and 20-30% of plastidic proteins are subject to NTA, NTA of mitochondrial proteins is rare. NTA alters key characteristics of proteins such as their three-dimensional structure, binding properties and lifetime. Since the majority of proteins is acetylated by five ribosome-bound N-terminal acetyltransferases (Nats) in yeast and humans, NTA was long perceived as an exclusively co-translational process in eukaryotes. The recent characterization of post-translationally acting plant Nats, which localize to the plasma membrane and the plastids, has challenged this view. Moreover, findings in humans, yeast, green algae and higher plants uncover differences in the cytosolic Nat machinery of photosynthetic and non-photosynthetic eukaryotes. These distinctive features of the plant Nat machinery might constitute adaptations to the sessile lifestyle of plants. This review sheds light on the unique role of plant N-acetyltransferases in development and stress responses as well as their evolution-driven adaptation to function in different cellular compartments.

Differential sensitivity of metabolic pathways in sugar beet roots to combined salt, heat, and light stress.

Plants in nature commonly encounter combined stress scenarios. The response to combined stressors is often unpredictable from the response to single stresses. To address stress interference in roots, we applied salinity, heat, and high light to hydroponically grown sugar beet. Two main patterns of metabolomic acclimation were apparent. High salt of 300 mM NaCl considerably lowered metabolite amounts, for example, those of most amino acids, γ-amino butyric acid (GABA), and glucose. Very few metabolites revealed the opposite trend with increased contents at high salts, mostly organic acids such as citric acid and isocitric acid, but also tryptophan, tyrosine, and the compatible solute proline. High temperature (31°C vs. 21°C) also frequently lowered root metabolite pools. The individual effects of salinity and heat were superimposed under combined stress. Under high light and high salt conditions, there was a significant decline in root chloride, mannitol, ribulose 5-P, cysteine, and l-aspartate contents. The results reveal the complex interaction pattern of environmental parameters and urge researchers to elaborate in much more detail and width on combinatorial stress effects to bridge work under controlled growth conditions to growth in nature, and also to better understand acclimation to the consequences of climate change.

Midwives' empathy and shared decision making from women's perspective - sensitivity of an assessment to compare quality of care in prenatal and obstetric care.

BACKGROUND: For quality-oriented evaluation of prenatal and obstetric care, it is important to systematically consider the perspective of the women receiving care in order to comprehensively assess and optimize quality in a woman-centered manner. Empathy and Shared Decision Making (SDM) are essential components of woman-centered midwifery care. The aim of the study was to analyze measurement invariance of the items of the Consultation and Relational Empathy (CARE) and Shared Decision Making-Questionnaire (SDM-Q-9) scales depending on the prenatal versus obstetric care setting. METHODS: One hundred fifty women retrospectively assessed aspects of woman-centered midwifery care in both prenatal and obstetric care setting. The birth of the child was a maximum of 12 months ago. A structural equation modelling approach was adopted to separate true effects from response shift (RS) effects depending on care setting. The latter were analyzed in terms of recalibration (changing women's internal measurement standards), Reprioritization (changing associations of items and construct) as well as Reconceptualization (redefining the target construct). RESULTS: A response shift model was identified for both assessments (pregnancy/birth: CFI = .96/.96; SRMR = .046/.051). At birth, both scales indicated lower quality of care compared with prenatal care (SDM-Q-9-M/CARE-8-M:|d| = 0.190/0.392). Although no reconceptualization is required for the items of both scales, RS effects are evident for individual items. Due to recalibration and reprioritization effects, the true differences in the items are partly underestimated (SDM-Q-9-M/CARE-8-M: 3/2 items) or overestimated (4/2 items). CONCLUSION: The structure of the constructs SDM and Empathy, indicating woman-centered midwifery care, are moderated by the care settings. To validly assess midwives' empathy and shared decision making from women's perspective, setting-dependent response shift effects have to be considered. The proven item-specific response effects contribute to a better understanding of construct characteristics in woman-centered care by midwives during pregnancy and childbirth.

MCU proteins dominate in vivo mitochondrial Ca2+ uptake in Arabidopsis roots.

Ca2+ signaling is central to plant development and acclimation. While Ca2+-responsive proteins have been investigated intensely in plants, only a few Ca2+-permeable channels have been identified, and our understanding of how intracellular Ca2+ fluxes is facilitated remains limited. Arabidopsis thaliana homologs of the mammalian channel-forming mitochondrial calcium uniporter (MCU) protein showed Ca2+ transport activity in vitro. Yet, the evolutionary complexity of MCU proteins, as well as reports about alternative systems and unperturbed mitochondrial Ca2+ uptake in knockout lines of MCU genes, leave critical questions about the in vivo functions of the MCU protein family in plants unanswered. Here, we demonstrate that MCU proteins mediate mitochondrial Ca2+ transport in planta and that this mechanism is the major route for fast Ca2+ uptake. Guided by the subcellular localization, expression, and conservation of MCU proteins, we generated an mcu triple knockout line. Using Ca2+ imaging in living root tips and the stimulation of Ca2+ transients of different amplitudes, we demonstrated that mitochondrial Ca2+ uptake became limiting in the triple mutant. The drastic cell physiological phenotype of impaired subcellular Ca2+ transport coincided with deregulated jasmonic acid-related signaling and thigmomorphogenesis. Our findings establish MCUs as a major mitochondrial Ca2+ entry route in planta and link mitochondrial Ca2+ transport with phytohormone signaling.

The plant TOR kinase tunes autophagy and meristem activity for nutrient stress-induced developmental plasticity.

Plants, unlike animals, respond to environmental challenges with comprehensive developmental transitions that allow them to cope with these stresses. Here we discovered that antagonistic activation of the Target of Rapamycin (TOR) kinase in Arabidopsis thaliana roots and shoots is essential for the nutrient deprivation-induced increase in the root-to-shoot ratio to improve foraging for mineral ions. We demonstrate that sulfate limitation-induced downregulation of TOR in shoots activates autophagy, resulting in enhanced carbon allocation to the root. The allocation of carbon to the roots is facilitated by the specific upregulation of the sucrose-transporter genes SWEET11/12 in shoots. SWEET11/12 activation is indispensable for enabling sucrose to act as a carbon source for growth and as a signal for tuning root apical meristem activity via glucose-TOR signaling. The sugar-stimulated TOR activity in the root suppresses autophagy and maintains root apical meristem activity to support root growth to enhance mining for new sulfate resources in the soil. We provide direct evidence that the organ-specific regulation of autophagy is essential for the increased root-to-shoot ratio in response to sulfur limitation. These findings uncover how sulfur limitation controls the central sensor kinase TOR to enable nutrient recycling for stress-induced morphological adaptation of the plant body.

Translational fidelity and growth of Arabidopsis require stress-sensitive diphthamide biosynthesis.

Diphthamide, a post-translationally modified histidine residue of eukaryotic TRANSLATION ELONGATION FACTOR2 (eEF2), is the human host cell-sensitizing target of diphtheria toxin. Diphthamide biosynthesis depends on the 4Fe-4S-cluster protein Dph1 catalyzing the first committed step, as well as Dph2 to Dph7, in yeast and mammals. Here we show that diphthamide modification of eEF2 is conserved in Arabidopsis thaliana and requires AtDPH1. Ribosomal -1 frameshifting-error rates are increased in Arabidopsis dph1 mutants, similar to yeast and mice. Compared to the wild type, shorter roots and smaller rosettes of dph1 mutants result from fewer formed cells. TARGET OF RAPAMYCIN (TOR) kinase activity is attenuated, and autophagy is activated, in dph1 mutants. Under abiotic stress diphthamide-unmodified eEF2 accumulates in wild-type seedlings, most strongly upon heavy metal excess, which is conserved in human cells. In summary, our results suggest that diphthamide contributes to the functionality of the translational machinery monitored by plants to regulate growth.

Discriminative Long-Distance Transport of Selenate and Selenite Triggers Glutathione Oxidation in Specific Subcellular Compartments of Root and Shoot Cells in Arabidopsis.

Selenium is an essential trace element required for seleno-protein synthesis in many eukaryotic cells excluding higher plants. However, a substantial fraction of organically bound selenide in human nutrition is directly or indirectly derived from plants, which assimilate inorganic selenium into organic seleno-compounds. In humans, selenium deficiency is associated with several health disorders Despite its importance for human health, selenium assimilation and metabolism is barely understood in plants. Here, we analyzed the impact of the two dominant forms of soil-available selenium, selenite and selenate, on plant development and selenium partitioning in plants. We found that the reference plant Arabidopsis thaliana discriminated between selenate and selenite application. In contrast to selenite, selenate was predominantly deposited in leaves. This explicit deposition of selenate caused chlorosis and impaired plant morphology, which was not observed upon selenite application. However, only selenate triggered the accumulation of the macronutrient sulfur, the sister element of selenium in the oxygen group. To understand the oxidation state-specific toxicity mechanisms for selenium in plants, we quantified the impact of selenate and selenite on the redox environment in the plastids and the cytosol in a time-resolved manner. Surprisingly, we found that selenite first caused the oxidation of the plastid-localized glutathione pool and had a marginal impact on the redox state of the cytosolic glutathione pool, specifically in roots. In contrast, selenate application caused more vigorous oxidation of the cytosolic glutathione pool but also impaired the plastidic redox environment. In agreement with the predominant deposition in leaves, the selenate-induced oxidation of both glutathione pools was more pronounced in leaves than in roots. Our results demonstrate that Se-species dependent differences in Se partitioning substantially contribute to whole plant Se toxicity and that these Se species have subcellular compartment-specific impacts on the glutathione redox buffer that correlate with toxicity symptoms.