SEC14-GOLD protein PATELLIN2 binds IRON-REGULATED TRANSPORTER1 linking root iron uptake to vitamin E.

Organisms require micronutrients, and Arabidopsis (Arabidopsis thaliana) IRON-REGULATED TRANSPORTER1 (IRT1) is essential for iron (Fe2+) acquisition into root cells. Uptake of reactive Fe2+ exposes cells to the risk of membrane lipid peroxidation. Surprisingly little is known about how this is avoided. IRT1 activity is controlled by an intracellular variable region (IRT1vr) that acts as a regulatory protein interaction platform. Here, we describe that IRT1vr interacted with peripheral plasma membrane SEC14-Golgi dynamics (SEC14-GOLD) protein PATELLIN2 (PATL2). SEC14 proteins bind lipophilic substrates and transport or present them at the membrane. To date, no direct roles have been attributed to SEC14 proteins in Fe import. PATL2 affected root Fe acquisition responses, interacted with ROS response proteins in roots, and alleviated root lipid peroxidation. PATL2 had high affinity in vitro for the major lipophilic antioxidant vitamin E compound α-tocopherol. Molecular dynamics simulations provided insight into energetic constraints and the orientation and stability of the PATL2-ligand interaction in atomic detail. Hence, this work highlights a compelling mechanism connecting vitamin E with root metal ion transport at the plasma membrane with the participation of an IRT1-interacting and α-tocopherol-binding SEC14 protein.

Cytokinin-promoted secondary growth and nutrient storage in the perennial stem zone of Arabis alpina.

Perennial plants maintain their lifespan through several growth seasons. Arabis alpina serves as a model Brassicaceae species to study perennial traits. Lateral stems of A. alpina have a proximal vegetative zone with a dormant bud zone and a distal senescing seed-producing inflorescence zone. We addressed how this zonation is distinguished at the anatomical level, whether it is related to nutrient storage and which signals affect the zonation. We found that the vegetative zone exhibits secondary growth, which we termed the perennial growth zone (PZ). High-molecular-weight carbon compounds accumulate there in cambium and cambium derivatives. Neither vernalization nor flowering were requirements for secondary growth and the sequestration of storage compounds. The inflorescence zone with only primary growth, termed the annual growth zone (AZ), or roots exhibited different storage characteristics. Following cytokinin application cambium activity was enhanced and secondary phloem parenchyma was formed in the PZ and also in the AZ. In transcriptome analysis, cytokinin-related genes represented enriched gene ontology terms and were expressed at a higher level in the PZ than in the AZ. Thus, A. alpina primarily uses the vegetative PZ for nutrient storage, coupled to cytokinin-promoted secondary growth. This finding lays a foundation for future studies addressing signals for perennial growth.

Comparative Transcriptomics of Lowland Rice Varieties Uncovers Novel Candidate Genes for Adaptive Iron Excess Tolerance.

Iron (Fe) toxicity is a major challenge for plant cultivation in acidic waterlogged soil environments, where lowland rice is a major staple food crop. Only few studies have addressed the molecular characterization of excess Fe tolerance in rice, and these highlight different mechanisms for Fe tolerance. Out of 16 lowland rice varieties, we identified a pair of contrasting lines, Fe-tolerant Lachit and -susceptible Hacha. The two lines differed in their physiological and morphological responses to excess Fe, including leaf growth, leaf rolling, reactive oxygen species generation and Fe and metal contents. These responses were likely due to genetic origin as they were mirrored by differential gene expression patterns, obtained through RNA sequencing, and corresponding gene ontology term enrichment in tolerant vs. susceptible lines. Thirty-five genes of the metal homeostasis category, mainly root expressed, showed differential transcriptomic profiles suggestive of an induced tolerance mechanism. Twenty-two out of these 35 metal homeostasis genes were present in selection sweep genomic regions, in breeding signatures, and/or differentiated during rice domestication. These findings suggest that Fe excess tolerance is an important trait in the domestication of lowland rice, and the identified genes may further serve to design the targeted Fe tolerance breeding of rice crops.

Putative cis-Regulatory Elements Predict Iron Deficiency Responses in Arabidopsis Roots.

Plant iron deficiency (-Fe) activates a complex regulatory network that coordinates root Fe uptake and distribution to sink tissues. In Arabidopsis (Arabidopsis thaliana), FER-LIKE FE DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT), a basic helix-loop-helix (bHLH) transcription factor (TF), regulates root Fe acquisition genes. Many other -Fe-induced genes are FIT independent, and instead regulated by other bHLH TFs and by yet unknown TFs. The cis-regulatory code, that is, the cis-regulatory elements (CREs) and their combinations that regulate plant -Fe-responses, remains largely elusive. Using Arabidopsis root transcriptome data and coexpression clustering, we identified over 100 putative CREs (pCREs) that predicted -Fe-induced gene expression in computational models. To assess pCRE properties and possible functions, we used large-scale in vitro TF binding data, positional bias, and evolutionary conservation. As one example, our approach uncovered pCREs resembling IDE1 (iron deficiency-responsive element 1), a known grass -Fe response CRE. Arabidopsis IDE1-likes were associated with FIT-dependent gene expression, more specifically with biosynthesis of Fe-chelating compounds. Thus, IDE1 seems to be conserved in grass and nongrass species. Our pCREs matched among others in vitro binding sites of B3, NAC, bZIP, and TCP TFs, which might be regulators of -Fe responses. Altogether, our findings provide a comprehensive source of cis-regulatory information for -Fe-responsive genes that advance our mechanistic understanding and inform future efforts in engineering plants with more efficient Fe uptake or transport systems.

Reactive oxygen species coordinate the transcriptional responses to iron availability in Arabidopsis.

Reactive oxygen species play a central role in the regulation of plant responses to environmental stress. Under prolonged iron (Fe) deficiency, increased levels of hydrogen peroxide (H2O2) initiate signaling events, resulting in the attenuation of Fe acquisition through the inhibition of FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT). As this H2O2 increase occurs in a FIT-dependent manner, our aim was to understand the processes involved in maintaining H2O2 levels under prolonged Fe deficiency and the role of FIT. We identified the CAT2 gene, encoding one of the three Arabidopsis catalase isoforms, as regulated by FIT. CAT2 loss-of-function plants displayed severe susceptibility to Fe deficiency and greatly increased H2O2 levels in roots. Analysis of the Fe homeostasis transcription cascade revealed that H2O2 influences the gene expression of downstream regulators FIT, BHLH genes of group Ib, and POPEYE (PYE); however, H2O2 did not affect their upstream regulators, such as BHLH104 and ILR3. Our data shows that FIT and CAT2 participate in a regulatory loop between H2O2 and prolonged Fe deficiency.

Improving mobility and participation of older people with vertigo, dizziness and balance disorders in primary care using a care pathway: feasibility study and process evaluation.

BACKGROUND: Community-dwelling older people are frequently affected by vertigo, dizziness and balance disorders (VDB). We previously developed a care pathway (CPW) to improve their mobility and participation by offering standardized approaches for general practitioners (GPs) and physical therapists (PTs). We aimed to assess the feasibility of the intervention, its implementation strategy and the study procedures in preparation for the subsequent main trial. METHODS: This 12-week prospective cohort feasibility study was accompanied by a process evaluation designed according to the UK Medical Research Council's Guidance for developing and evaluating complex interventions. Patients with VDB (≥65 years), GPs and PTs in primary care were included. The intervention consisted of a diagnostic screening checklist for GPs and a guide for PTs. The implementation strategy included specific educational trainings and a telephone helpline. Data for mixed-method process evaluation were collected via standardized questionnaires, field notes and qualitative interviews. Quantitative data were analysed using descriptive statistics, qualitative data using content analysis. RESULTS: A total of five GP practices (seven single GPs), 10 PT practices and 22 patients were included in the study. The recruitment of GPs and patients was challenging (response rates: GP practices: 28%, PT practices: 39%). Ninety-one percent of the patients and all health professionals completed the study. The health professionals responded well to the educational trainings; the utilization of the telephone helpline was low (one call each from GPs and PTs). Familiarisation with the routine of application of the intervention and positive attitudes were emphasized as facilitators of the implementation of the intervention, whereas a lack of time was mentioned as a barrier. Despite difficulties in the GPs' adherence to the intervention protocol, the GPs, PTs and patients saw benefit in the intervention. The patients' treatment adherence to physical therapy was good. There were minor issues in data collection, but no unintended consequences. CONCLUSION: Although the process evaluation provided good support for the feasibility of study procedures, the intervention and its implementation strategy, we identified a need for improvement in recruitment of participants, the GP intervention part and the data collection procedures. The findings will inform the main trial to test the interventions effectiveness in a cluster RCT. TRIAL REGISTRATION: Projektdatenbank Versorgungsforschung Deutschland (German registry Health Services Research) VfD_MobilE-PHY_17_003910, date of registration: 30.11.2017; Deutsches Register Klinischer Studien (German Clinical Trials Register) DRKS00022918, date of registration: 03.09.2020 (retrospectively registered).

Development of a complex intervention to improve mobility and participation of older people with vertigo, dizziness and balance disorders in primary care: a mixed methods study.

BACKGROUND: Vertigo, dizziness and balance disorders (VDB) are common in older people and cause restrictions in mobility and social participation. Due to a multifactorial aetiology, health care is often overutilised, but many patients are also treated insufficiently in primary care. The purpose of this study was to develop a care pathway as a complex intervention to improve mobility and participation in older people with VDB in primary care. METHODS: The development process followed the UK Medical Research Council guidance using a mixed-methods design with individual and group interviews carried out with patients, physical therapists (PTs), general practitioners (GPs), nurses working in community care and a multi-professional expert panel to create a first draft of a care pathway (CPW) and implementation strategy using the Consolidated Framework of Implementation Research and the Expert recommendations for Implementing Change. Subsequently, small expert group modelling of specific components of the CPW was carried out, with GPs, medical specialists and PTs. The Behaviour Change Wheel was applied to design the intervention´s approach to behaviour change. To derive theoretical assumptions, we adopted Kellogg´s Logic Model to consolidate the hypothesized chain of causes leading to patient-relevant outcomes. RESULTS: Individual interviews with patients showed that VDB symptoms need to be taken more seriously by GPs. Patients demanded age-specific treatment offers, group sessions or a continuous mentoring by a PT. GPs required a specific guideline for diagnostics and treatment options including psychosocial interventions. Specific assignment to and a standardized approach during physical therapy were desired by PTs. Nurses favoured a multi-professional documentation system. The structured three-day expert workshop resulted in a first draft of CPW and potential implementation strategies. Subsequent modelling resulted in a CPW with components and appropriate training materials for involved health professionals. A specific implementation strategy is now available. CONCLUSION: A mixed-methods design was suggested to be a suitable approach to develop a complex intervention and its implementation strategy. We will subsequently test the intervention for its acceptability and feasibility in a feasibility study accompanied by a comprehensive process evaluation to inform a subsequent effectiveness trial. TRIAL REGISTRATION: The research project is registered in "Projektdatenbank Versorgungsforschung Deutschland" (Project-ID: VfD_MobilE-PHY_17_003910; date of registration: 30.11.2017).

Phylogenetic analysis of plant multi-domain SEC14-like phosphatidylinositol transfer proteins and structure-function properties of PATELLIN2.

KEY MESSAGE: SEC14L-PITPs guide membrane recognition and signaling. An increasingly complex modular structure of SEC14L-PITPs evolved in land plants compared to green algae. SEC14/CRAL-TRIO and GOLD domains govern membrane binding specificity. SEC14-like phosphatidylinositol transfer proteins (SEC14L-PITPs) provide cues for membrane identity by exchanging lipophilic substrates, ultimately governing membrane signaling. Flowering plant SEC14L-PITPs often have modular structure and are associated with cell division, development, and stress responses. Yet, structure-function relationships for biochemical-cellular interactions of SEC14L-PITPs are rather enigmatic. Here, we evaluate the phylogenetic relationships of the SEC14L-PITP superfamily in the green lineage. Compared to green algae, land plants have an extended set of SEC14L-PITPs with increasingly complex modular structure. SEC14-GOLD PITPs, present in land plants but not Chara, diverged to three functional subgroups, represented by the six PATELLIN (PATL) proteins in Arabidopsis. Based on the example of Arabidopsis PATL2, we dissect the functional domains for in vitro binding to phosphoinositides and liposomes and for plant cell membrane association. While the SEC14 domain and its CRAL-TRIO-N-terminal extension serve general membrane attachment of the protein, the C-terminal GOLD domain directs it to the plasma membrane by recognizing specific phosphoinositides. We discuss that the different domains of SEC14L-PITPs integrate developmental and environmental signals to control SEC14L-PITP-mediated membrane identity, important to initiate dynamic membrane events.

Phospho-mutant activity assays provide evidence for alternative phospho-regulation pathways of the transcription factor FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR.

The key basic helix-loop-helix (bHLH) transcription factor in iron (Fe) uptake, FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT), is controlled by multiple signaling pathways, important to adjust Fe acquisition to growth and environmental constraints. FIT protein exists in active and inactive protein pools, and phosphorylation of serine Ser272 in the C-terminus, a regulatory domain of FIT, provides a trigger for FIT activation. Here, we use phospho-mutant activity assays and study phospho-mimicking and phospho-dead mutations of three additional predicted phosphorylation sites, namely at Ser221 and at tyrosines Tyr238 and Tyr278, besides Ser 272. Phospho-mutations at these sites affect FIT activities in yeast, plant, and mammalian cells. The diverse array of cellular phenotypes is seen at the level of cellular localization, nuclear mobility, homodimerization, and dimerization with the FIT-activating partner bHLH039, promoter transactivation, and protein stability. Phospho-mimicking Tyr mutations of FIT disturb fit mutant plant complementation. Taken together, we provide evidence that FIT is activated through Ser and deactivated through Tyr site phosphorylation. We therefore propose that FIT activity is regulated by alternative phosphorylation pathways.

Calcium-Promoted Interaction between the C2-Domain Protein EHB1 and Metal Transporter IRT1 Inhibits Arabidopsis Iron Acquisition.

Iron is a key transition element in the biosphere and is crucial for living organisms, although its cellular excess can be deleterious. Maintaining the balance of optimal iron availability in the model plant Arabidopsis (Arabidopsis thaliana) requires the precise operation of iron import through the principal iron transporter IRON-REGULATED TRANSPORTER1 (IRT1). Targeted inhibition of IRT1 can prevent oxidative stress, thus promoting plant survival. Here, we report the identification of an IRT1 inhibitor, namely the C2 domain-containing peripheral membrane protein ENHANCED BENDING1 (EHB1). EHB1 interacts with the cytoplasmically exposed variable region of IRT1, and we demonstrate that this interaction is greatly promoted by the presence of calcium. We found that EHB1 binds lipids characteristic of the plasma membrane, and the interaction between EHB1 and plant membranes is calcium-dependent. Molecular simulations showed that EHB1 membrane binding is a two-step process that precedes the interaction between EHB1 and IRT1. Genetic and physiological analyses indicated that EHB1 acts as a negative regulator of iron acquisition. The presence of EHB1 prevented the IRT1-mediated complementation of iron-deficient fet3fet4 yeast (Saccharomyces cerevisiae). Our data suggest that EHB1 acts as a direct inhibitor of IRT1-mediated iron import into the cell. These findings represent a major step in understanding plant iron acquisition, a process that underlies the primary production of bioavailable iron for land ecosystems.

FIT, a regulatory hub for iron deficiency and stress signaling in roots, and FIT-dependent and -independent gene signatures.

Iron (Fe) is vital for plant growth. Plants balance the beneficial and toxic effects of this micronutrient, and tightly control Fe uptake and allocation. Here, we review the role of the basic helix-loop-helix (bHLH) transcription factor FIT (FER-LIKE FE DEFICIENCY-INDUCED TRANSCRIPTION FACTOR) in Fe acquisition. FIT is not only essential, it is also a central regulatory hub in root cells to steer and adjust the rate of Fe uptake by the root in a changing environment. FIT regulates a subset of root Fe deficiency (-Fe) response genes. Based on a combination of co-expression network and FIT-dependent transcriptome analyses, we defined a set of FIT-dependent and FIT-independent gene expression signatures and co-expression clusters that encode specific functions in Fe regulation and Fe homeostasis. These gene signatures serve as markers to integrate novel regulatory factors and signals into the -Fe response cascade. FIT forms a complex with bHLH subgroup Ib transcription factors. Furthermore, it interacts with key regulators from different signaling pathways that either activate or inhibit FIT function to adjust Fe acquisition to growth and environmental constraints. Co-expression clusters and FIT protein interactions suggest a connection of -Fe with ABA responses and root cell elongation processes that can be explored in future studies.

Physical therapy interventions for older people with vertigo, dizziness and balance disorders addressing mobility and participation: a systematic review.

BACKGROUND: Vertigo, dizziness and balance disorders (VDB) are among the most relevant contributors to the burden of disability among older adults living in the community and associated with immobility, limitations of activities of daily living and decreased participation. The aim of this study was to identify the quality of evidence of physical therapy interventions that address mobility and participation in older patients with VDB and to characterize the used primary and secondary outcomes. METHODS: A systematic search via MEDLINE (PubMed), Cochrane Library, CINAHL, PEDro, forward citation tracing and hand search was conducted initially in 11/2017 and updated in 7/2019. We included individual and cluster-randomized controlled trials and trials with quasi-experimental design, published between 2007 and 2017/2019 and including individuals ≥65 years with VDB. Physical therapy and related interventions were reviewed with no restrictions to outcome measurement. Screening of titles, abstracts and full texts, data extraction and critical appraisal was conducted by two independent researchers. The included studies were heterogeneous in terms of interventions and outcome measures. Therefore, a narrative synthesis was conducted. RESULTS: A total of 20 randomized and 2 non-randomized controlled trials with 1876 patients met the inclusion criteria. The included studies were heterogeneous in terms of complexity of interventions, outcome measures and methodological quality. Vestibular rehabilitation (VR) was examined in twelve studies, computer-assisted VR (CAVR) in five, Tai Chi as VR (TCVR) in three, canal repositioning manoeuvres (CRM) in one and manual therapy (MT) in one study. Mixed effects were found regarding body structure/function and activities/participation. Quality of life and/or falls were assessed, with no differences between groups. VR is with moderate quality of evidence superior to usual care to improve balance, mobility and symptoms. CONCLUSION: To treat older individuals with VDB, VR in any variation and in addition to CRMs seems to be effective. High-quality randomized trials need to be conducted to inform clinical decision making. TRIAL REGISTRATION: PROSPERO 2017 CRD42017080291 .

Barriers to and facilitators of the implementation of multi-disciplinary care pathways in primary care: a systematic review.

BACKGROUND: Care pathways (CPWs) are complex interventions that have the potential to reduce treatment errors and optimize patient outcomes by translating evidence into local practice. To design an optimal implementation strategy, potential barriers to and facilitators of implementation must be considered. The objective of this systematic review is to identify barriers to and facilitators of the implementation of CPWs in primary care (PC). METHODS: A systematic search via Cochrane Library, CINAHL, and MEDLINE via PubMed supplemented by hand searches and citation tracing was carried out. We considered articles reporting on CPWs targeting patients at least 65 years of age in outpatient settings that were written in the English or German language and were published between 2007 and 2019. We considered (non-)randomized controlled trials, controlled before-after studies, interrupted time series studies (main project reports) as well as associated process evaluation reports of either methodology. Two independent researchers performed the study selection; the data extraction and critical appraisal were duplicated until the point of perfect agreement between the two reviewers. Due to the heterogeneity of the included studies, a narrative synthesis was performed. RESULTS: Fourteen studies (seven main project reports and seven process evaluation reports) of the identified 8154 records in the search update were included in the synthesis. The structure and content of the interventions as well as the quality of evidence of the studies varied. The identified barriers and facilitators were classified using the Context and Implementation of Complex Interventions framework. The identified barriers were inadequate staffing, insufficient education, lack of financial compensation, low motivation and lack of time. Adequate skills and knowledge through training activities for health professionals, good multi-disciplinary communication and individual tailored interventions were identified as facilitators. CONCLUSIONS: In the implementation of CPWs in PC, a multitude of barriers and facilitators must be considered, and most of them can be modified through the careful design of intervention and implementation strategies. Furthermore, process evaluations must become a standard component of implementing CPWs to enable other projects to build upon previous experience. TRIAL REGISTRATION: PROSPERO 2018 CRD42018087689.

Nutrient exchange in arbuscular mycorrhizal symbiosis from a thermodynamic point of view.

To obtain insights into the dynamics of nutrient exchange in arbuscular mycorrhizal (AM) symbiosis, we modelled mathematically the two-membrane system at the plant-fungus interface and simulated its dynamics. In computational cell biology experiments, the full range of nutrient transport pathways was tested for their ability to exchange phosphorus (P)/carbon (C)/nitrogen (N) sources. As a result, we obtained a thermodynamically justified, independent and comprehensive model of the dynamics of the nutrient exchange at the plant-fungus contact zone. The predicted optimal transporter network coincides with the transporter set independently confirmed in wet-laboratory experiments previously, indicating that all essential transporter types have been discovered. The thermodynamic analyses suggest that phosphate is released from the fungus via proton-coupled phosphate transporters rather than anion channels. Optimal transport pathways, such as cation channels or proton-coupled symporters, shuttle nutrients together with a positive charge across the membranes. Only in exceptional cases does electroneutral transport via diffusion facilitators appear to be plausible. The thermodynamic models presented here can be generalized and adapted to other forms of mycorrhiza and open the door for future studies combining wet-laboratory experiments with computational simulations to obtain a deeper understanding of the investigated phenomena.

ZINC FINGER OF ARABIDOPSIS THALIANA12 (ZAT12) Interacts with FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT) Linking Iron Deficiency and Oxidative Stress Responses.

Plants grown under iron (Fe)-deficient conditions induce a set of genes that enhance the efficiency of Fe uptake by the roots. In Arabidopsis (Arabidopsis thaliana), the central regulator of this response is the basic helix-loop-helix transcription factor FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT). FIT activity is regulated by protein-protein interactions, which also serve to integrate external signals that stimulate and possibly inhibit Fe uptake. In the search of signaling components regulating FIT function, we identified ZINC FINGER OF ARABIDOPSIS THALIANA12 (ZAT12), an abiotic stress-induced transcription factor. ZAT12 interacted with FIT, dependent on the presence of the ethylene-responsive element-binding factor-associated amphiphilic repression motif. ZAT12 protein was found expressed in the root early differentiation zone, where its abundance was modulated in a root layer-specific manner. In the absence of ZAT12, FIT expression was upregulated, suggesting a negative effect of ZAT12 on Fe uptake. Consistently, zat12 loss-of-function mutants had higher Fe content than the wild type at sufficient Fe. We found that under Fe deficiency, hydrogen peroxide (H2O2) levels were enhanced in a FIT-dependent manner. FIT protein, in turn, was stabilized by H2O2 but only in the presence of ZAT12, showing that H2O2 serves as a signal for Fe deficiency responses. We propose that oxidative stress-induced ZAT12 functions as a negative regulator of Fe acquisition. A model where H2O2 mediates the negative regulation of plant responses to prolonged stress might be applicable to a variety of stress conditions.

SORTING NEXIN1 is required for modulating the trafficking and stability of the Arabidopsis IRON-REGULATED TRANSPORTER1.

Dicotyledonous plants growing under limited iron availability initiate a response resulting in the solubilization, reduction, and uptake of soil iron. The protein factors responsible for these steps are transmembrane proteins, suggesting that the intracellular trafficking machinery may be involved in iron acquisition. In search for components involved in the regulation of Arabidopsis thaliana iron deficiency responses, we identified the members of the SORTING NEXIN (SNX) protein family. SNX loss-of-function plants display enhanced susceptibility to iron deficiency in comparison to the wild type. The absence of SNX led to reduced iron import efficiency into the root. SNX1 showed partial colocalization with the principal root iron importer IRON-REGULATED TRANSPORTER1 (IRT1). In SNX loss-of-function plants, IRT1 protein levels were decreased compared with the wild type due to enhanced IRT1 degradation. This resulted in diminished amounts of the IRT1 protein at the plasma membrane. snx mutants exhibited enhanced iron deficiency responses compared with the wild type, presumably due to the lower iron uptake through IRT1. Our results reveal a role of SNX1 for the correct trafficking of IRT1 and, thus, for modulating the activity of the iron uptake machinery.

Iron homeostasis in Arabidopsis thaliana: transcriptomic analyses reveal novel FIT-regulated genes, iron deficiency marker genes and functional gene networks.

BACKGROUND: FIT (FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR) is the central regulator of iron uptake in Arabidopsis thaliana roots. We performed transcriptome analyses of six day-old seedlings and roots of six week-old plants using wild type, a fit knock-out mutant and a FIT over-expression line grown under iron-sufficient or iron-deficient conditions. We compared genes regulated in a FIT-dependent manner depending on the developmental stage of the plants. We assembled a high likelihood dataset which we used to perform co-expression and functional analysis of the most stably iron deficiency-induced genes. RESULTS: 448 genes were found FIT-regulated. Out of these, 34 genes were robustly FIT-regulated in root and seedling samples and included 13 novel FIT-dependent genes. Three hundred thirty-one genes showed differential regulation in response to the presence and absence of FIT only in the root samples, while this was the case for 83 genes in the seedling samples. We assembled a virtual dataset of iron-regulated genes based on a total of 14 transcriptomic analyses of iron-deficient and iron-sufficient wild-type plants to pinpoint the best marker genes for iron deficiency and analyzed this dataset in depth. Co-expression analysis of this dataset revealed 13 distinct regulons part of which predominantly contained functionally related genes. CONCLUSIONS: We could enlarge the list of FIT-dependent genes and discriminate between genes that are robustly FIT-regulated in roots and seedlings or only in one of those. FIT-regulated genes were mostly induced, few of them were repressed by FIT. With the analysis of a virtual dataset we could filter out and pinpoint new candidates among the most reliable marker genes for iron deficiency. Moreover, co-expression and functional analysis of this virtual dataset revealed iron deficiency-induced and functionally distinct regulons.

Iron and FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR-dependent regulation of proteins and genes in Arabidopsis thaliana roots.

Iron is an essential micronutrient for plants, and iron deficiency requires a variety of physiological adaptations. FIT (FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR) is essential for the regulation of iron uptake in Arabidopsis thaliana roots. FIT is transcriptionally as well as posttranscriptionally regulated in response to iron supply. To investigate to which extent posttranscriptional regulation upon iron deficiency applies to proteins and to determine the dependency on FIT, we performed a parallel proteomic and transcriptomic study with wild-type, a fit knock-out mutant, and a FIT overexpressing Arabidopsis line. Among 92 proteins differentially regulated by iron and/or FIT, we identified 30 proteins, which displayed differential regulation at the transcriptional level. Eleven protein spots were regulated in at least one of the data points even contrary to the respective genes dependent on FIT. We found ten proteins in at least two forms. The analysis of functional classification showed enriched GO terms among the posttranscriptionally regulated genes and of proteins, that were downregulated or absent in the fit knock-out mutant. Taken together, we provide evidence for iron and FIT-dependent posttranscriptional regulation in iron homeostasis in A. thaliana.

Nicotianamine functions in the Phloem-based transport of iron to sink organs, in pollen development and pollen tube growth in Arabidopsis.

The metal chelator nicotianamine promotes the bioavailability of Fe and reduces cellular Fe toxicity. For breeding Fe-efficient crops, we need to explore the fundamental impact of nicotianamine on plant development and physiology. The quadruple nas4x-2 mutant of Arabidopsis thaliana cannot synthesize any nicotianamine, shows strong leaf chlorosis, and is sterile. To date, these phenotypes have not been fully explained. Here, we show that sink organs of this mutant were Fe deficient, while aged leaves were Fe sufficient. Upper organs were also Zn deficient. We demonstrate that transport of Fe to aged leaves relied on citrate, which partially complemented the loss of nicotianamine. In the absence of nicotianamine, Fe accumulated in the phloem. Our results show that rather than enabling the long-distance movement of Fe in the phloem (as is the case for Zn), nicotianamine facilitates the transport of Fe from the phloem to sink organs. We delimit nicotianamine function in plant reproductive biology and demonstrate that nicotianamine acts in pollen development in anthers and pollen tube passage in the carpels. Since Fe and Zn both enhance pollen germination, a lack of either metal may contribute to the reproductive defect. Our study sheds light on the physiological functions of nicotianamine.

Functional electrical stimulation-assisted active cycling--therapeutic effects in patients with hemiparesis from 7 days to 6 months after stroke: a randomized controlled pilot study.

OBJECTIVE: To determine whether functional electrical stimulation (FES)-assisted active cycling is more effective than active cycling without FES concerning walking and balance. Specifically, walking ability was classified as to the amount of personal assistance needed to be able to walk and balance was evaluated for static and dynamic balance tasks. DESIGN: Monocentric, randomized, single-blinded, controlled trial. SETTING: Neurologic rehabilitation hospital. PARTICIPANTS: Patients with severe hemiparesis due to stroke (N=40). INTERVENTIONS: Twenty minutes of active leg cycling with or without FES applied to the paretic vastus medialis and rectus femoris of quadriceps and to the biceps femoris and semitendinosus muscles, 3 times/wk for 4 weeks. MAIN OUTCOME MEASURES: Functional ambulation classification (FAC) and performance-oriented mobility assessment (POMA) were the primary outcome measures. The leg subscale of the motricity index (MI) and the modified Ashworth scale were the secondary outcome measures. Evaluation was done before and after the intervention period and after an additional 2 weeks. RESULTS: After the intervention, the FAC, POMA, and the MI (P<.016) for both intervention groups improved significantly. The FAC of the control group increased by a median of 1 category and that of the FES group by 2 categories. The median change in POMA was 2 and 4 points for the control group and the FES group, respectively. The Mann-Whitney U test between-group comparisons revealed that these gains were significantly better in the FES group for both the FAC (U=90; z=-2.58; P=.013; r=-.42) and the POMA (U=60; z=-3.43; P<.0004; r=-.56). Because of missing data and slightly decreased effect sizes during the follow-up phase (FAC, r=-.33; POMA, r=-.41), differences did not reach statistically significant P values. The MI leg subscale showed significant improvements in both groups. However, there were no significant differences between the groups at any time. No changes were observed on the modified Ashworth scale. CONCLUSIONS: FES-assisted active cycling seems to be a promising intervention during rehabilitation in patients with stroke.