Synthesis and import of GDP-l-fucose into the Golgi affect plant-water relations.

Land plants evolved multiple adaptations to restrict transpiration. However, the underlying molecular mechanisms are not sufficiently understood. We used an ozone-sensitivity forward genetics approach to identify Arabidopsis thaliana mutants impaired in gas exchange regulation. High water loss from detached leaves and impaired decrease of leaf conductance in response to multiple stomata-closing stimuli were identified in a mutant of MURUS1 (MUR1), an enzyme required for GDP-l-fucose biosynthesis. High water loss observed in mur1 was independent from stomatal movements and instead could be linked to metabolic defects. Plants defective in import of GDP-l-Fuc into the Golgi apparatus phenocopied the high water loss of mur1 mutants, linking this phenotype to Golgi-localized fucosylation events. However, impaired fucosylation of xyloglucan, N-linked glycans, and arabinogalactan proteins did not explain the aberrant water loss of mur1 mutants. Partial reversion of mur1 water loss phenotype by borate supplementation and high water loss observed in boron uptake mutants link mur1 gas exchange phenotypes to pleiotropic consequences of l-fucose and boron deficiency, which in turn affect mechanical and morphological properties of stomatal complexes and whole-plant physiology. Our work emphasizes the impact of fucose metabolism and boron uptake on plant-water relations.

Nitric oxide-releasing nanomaterials: from basic research to potential biotechnological applications in agriculture.

Nitric oxide (NO) is a multifunctional gaseous signal that modulates the growth, development and stress tolerance of higher plants. NO donors have been used to boost plant endogenous NO levels and to activate NO-related responses, but this strategy is often hindered by the relative instability of donors. Alternatively, nanoscience offers a new, promising way to enhance NO delivery to plants, as NO-releasing nanomaterials (e.g. S-nitrosothiol-containing chitosan nanoparticles) have many beneficial physicochemical and biochemical properties compared to non-encapsulated NO donors. Nano NO donors are effective in increasing tissue NO levels and enhancing NO effects both in animal and human systems. The authors believe, and would like to emphasize, that new trends and technologies are essential for advancing plant NO research and nanotechnology may represent a breakthrough in traditional agriculture and environmental science. Herein, we aim to draw the attention of the scientific community to the potential of NO-releasing nanomaterials in both basic and applied plant research as alternatives to conventional NO donors, providing a brief overview of the current knowledge and identifying future research directions. We also express our opinion about the challenges for the application of nano NO donors, such as the environmental footprint and stakeholder's acceptance of these materials.

Nitric oxide coordinates growth, development, and stress response via histone modification and gene expression.

Nitric oxide (NO) is a signaling molecule with multiple regulatory functions in plant physiology and stress response. In addition to direct effects on transcriptional machinery, NO executes its signaling function via epigenetic mechanisms. We report that light intensity-dependent changes in NO correspond to changes in global histone acetylation (H3, H3K9, and H3K9/K14) in Arabidopsis (Arabidopsis thaliana) wild-type leaves, and that this relationship depends on S-nitrosoglutathione reductase and histone deacetylase 6 (HDA6). The activity of HDA6 was sensitive to NO, demonstrating that NO participates in regulation of histone acetylation. Chromatin immunoprecipitation sequencing and RNA-seq analyses revealed that NO participates in the metabolic switch from growth and development to stress response. This coordinating function of NO might be particularly important in plant ability to adapt to a changing environment, and is therefore a promising foundation for mitigating the negative effects of climate change on plant productivity.

Ragweed plants grown under elevated CO2 levels produce pollen which elicit stronger allergic lung inflammation.

BACKGROUND: Common ragweed has been spreading as a neophyte in Europe. Elevated CO2 levels, a hallmark of global climate change, have been shown to increase ragweed pollen production, but their effects on pollen allergenicity remain to be elucidated. METHODS: Ragweed was grown in climate-controlled chambers under normal (380 ppm, control) or elevated (700 ppm, based on RCP4.5 scenario) CO2 levels. Aqueous pollen extracts (RWE) from control- or CO2 -pollen were administered in vivo in a mouse model for allergic disease (daily for 3-11 days, n = 5) and employed in human in vitro systems of nasal epithelial cells (HNECs), monocyte-derived dendritic cells (DCs), and HNEC-DC co-cultures. Additionally, adjuvant factors and metabolites in control- and CO2 -RWE were investigated using ELISA and untargeted metabolomics. RESULTS: In vivo, CO2 -RWE induced stronger allergic lung inflammation compared to control-RWE, as indicated by lung inflammatory cell infiltrate and mediators, mucus hypersecretion, and serum total IgE. In vitro, HNECs stimulated with RWE increased indistinctively the production of pro-inflammatory cytokines (IL-8, IL-1ß, and IL-6). In contrast, supernatants from CO2 -RWE-stimulated HNECs, compared to control-RWE-stimulated HNECS, significantly increased TNF and decreased IL-10 production in DCs. Comparable results were obtained by stimulating DCs directly with RWEs. The metabolome analysis revealed differential expression of secondary plant metabolites in control- vs CO2 -RWE. Mixes of these metabolites elicited similar responses in DCs as compared to respective RWEs. CONCLUSION: Our results indicate that elevated ambient CO2 levels elicit a stronger RWE-induced allergic response in vivo and in vitro and that RWE increased allergenicity depends on the interplay of multiple metabolites.

Recommendations on terminology and experimental best practice associated with plant nitric oxide research.

Nitric oxide (NO) emerged as a key signal molecule in plants. During the last two decades impressive progress has been made in plant NO research. This small, redox-active molecule is now known to play an important role in plant immunity, stress responses, environmental interactions, plant growth and development. To more accurately and robustly establish the full spectrum of NO bioactivity in plants, it will be essential to apply methodological best practice. In addition, there are some instances of conflicting nomenclature within the field, which would benefit from standardization. In this context, we attempt to provide some helpful guidance for best practice associated with NO research and also suggestions for the cognate terminology.

Regulating the regulator: nitric oxide control of post-translational modifications.

Nitric oxide (NO) is perfectly suited for the role of a redox signalling molecule. A key route for NO bioactivity occurs via protein S-nitrosation, and involves the addition of a NO moiety to a protein cysteine (Cys) thiol (-SH) to form an S-nitrosothiol (SNO). This process is thought to underpin a myriad of cellular processes in plants that are linked to development, environmental responses and immune function. Here we collate emerging evidence showing that NO bioactivity regulates a growing number of diverse post-translational modifications including SUMOylation, phosphorylation, persulfidation and acetylation. We provide examples of how NO orchestrates these processes to mediate plant adaptation to a variety of cellular cues.

A T-DNA mutant screen that combines high-throughput phenotyping with the efficient identification of mutated genes by targeted genome sequencing.

BACKGROUND: Nitrogen dioxide (NO2) triggers hypersensitive response (HR)-like cell death in Arabidopsis thaliana. A high-throughput mutant screen was established to identify genes involved in this type of programmed cell death. RESULTS: Altogether 14,282 lines of SALK T-DNA insertion mutants were screened. Growing 1000 pooled mutant lines per tray and simultaneous NO2 fumigation of 4 trays in parallel facilitated high-throughput screening. Candidate mutants were selected based on visible symptoms. Sensitive mutants showed lesions already after fumigation for 1 h with 10 ppm (ppm) NO2 whereas tolerant mutants were hardly damaged even after treatment with 30 ppm NO2. Identification of T-DNA insertion sites by adapter ligation-mediated PCR turned out to be successful but rather time consuming. Therefore, next generation sequencing after T-DNA-specific target enrichment was tested as an alternative screening method. The targeted genome sequencing was highly efficient due to (1.) combination of the pooled DNA from 124 candidate mutants in only two libraries, (2.) successful target enrichment using T-DNA border-specific 70mer probes, and (3.) stringent filtering of the sequencing reads. Seventy mutated genes were identified by at least 3 sequencing reads. Ten corresponding mutants were re-screened of which 8 mutants exhibited NO2-sensitivity or -tolerance confirming that the screen yielded reliable results. Identified candidate genes had published functions in HR, pathogen resistance, and stomata regulation. CONCLUSIONS: The presented NO2 dead-or-alive screen combined with next-generation sequencing after T-DNA-specific target enrichment was highly efficient. Two researchers finished the screen within 3 months. Moreover, the target enrichment approach was cost-saving because of the limited number of DNA libraries and sequencing runs required. The experimental design can be easily adapted to other screening approaches e.g. involving high-throughput treatments with abiotic stressors or phytohormones.

Short-Term Exposure to Nitrogen Dioxide Provides Basal Pathogen Resistance.

Nitrogen dioxide (NO2) forms in plants under stress conditions, but little is known about its physiological functions. Here, we explored the physiological functions of NO2 in plant cells using short-term fumigation of Arabidopsis (Arabidopsis thaliana) for 1 h with 10 µL L-1 NO2. Although leaf symptoms were absent, the expression of genes related to pathogen resistance was induced. Fumigated plants developed basal disease resistance, or pattern-triggered immunity, against the necrotrophic fungus Botrytis cinerea and the hemibiotrophic bacterium Pseudomonas syringae Functional salicylic acid and jasmonic acid (JA) signaling pathways were both required for the full expression of NO2-induced resistance against B. cinerea An early peak of salicylic acid accumulation immediately after NO2 exposure was followed by a transient accumulation of oxophytodienoic acid. The simultaneous NO2-induced expression of genes involved in jasmonate biosynthesis and jasmonate catabolism resulted in the complete suppression of JA and JA-isoleucine (JA-Ile) accumulation, which was accompanied by a rise in the levels of their catabolic intermediates 12-OH-JA, 12-OH-JA-Ile, and 12-COOH-JA-Ile. NO2-treated plants emitted the volatile monoterpene α-pinene and the sesquiterpene longifolene (syn. junipene), which could function in signaling or direct defense against pathogens. NO2-triggered B. cinerea resistance was dependent on enhanced early callose deposition and CYTOCHROME P450 79B2 (CYP79B2), CYP79B3, and PHYTOALEXIN DEFICIENT3 gene functions but independent of camalexin, CYP81F2, and 4-OH-indol-3-ylmethylglucosinolate derivatives. In sum, exogenous NO2 triggers basal pathogen resistance, pointing to a possible role for endogenous NO2 in defense signaling. Additionally, this study revealed the involvement of jasmonate catabolism and volatiles in pathogen immunity.

Phytoglobin overexpression promotes barley growth in the presence of enhanced level of atmospheric nitric oxide.

To investigate the effect of high atmospheric NO concentrations on crop plants and the role of phytoglobins under these conditions, we performed a long-term study on barley 'Golden Promise' wild type (WT), class 1 phytoglobin knockdown (HvPgb1.1-) and class 1 phytoglobin overexpression (HvPgb1.1+) lines. Plants were cultivated with nitrogen-free nutrient solution during the entire growth period and were fumigated with different NO concentration (ambient, 800, 1500, and 3000 ppb). Analysis of fresh weight, stem number, chlorophyll content, and effective quantum yield of PSII showed that NO fumigation promoted plant growth and tillering significantly in the HvPgb1.1+ line. After 80 d of NO fumigation, dry matter weight, spikes number, kernel number, and plant kernel weight were significantly increased in HvPgb1.1+ plants with increasing NO concentration. In contrast, yield decreased in WT and HvPgb1.1- plants the higher the NO level. Application of atmospheric 15NO and 15NO2 demonstrated NO specificity of phytoglobins. 15N from 15NO could be detected in RNA, DNA, and proteins of barley leaves and the 15N levels were significantly higher in HvPgb1.1+ plants in comparison with HvPgb1.1- and WT plants. Our results demonstrate that overexpression of phytoglobins allows plants to more efficiently use atmospheric NO as N source.

Nitric Oxide Modulates Histone Acetylation at Stress Genes by Inhibition of Histone Deacetylases.

Histone acetylation, which is an important mechanism to regulate gene expression, is controlled by the opposing action of histone acetyltransferases and histone deacetylases (HDACs). In animals, several HDACs are subjected to regulation by nitric oxide (NO); in plants, however, it is unknown whether NO affects histone acetylation. We found that treatment with the physiological NO donor S-nitrosoglutathione (GSNO) increased the abundance of several histone acetylation marks in Arabidopsis (Arabidopsis thaliana), which was strongly diminished in the presence of the NO scavenger 2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide. This increase was likely triggered by NO-dependent inhibition of HDAC activity, since GSNO and S-nitroso-N-acetyl-dl-penicillamine significantly and reversibly reduced total HDAC activity in vitro (in nuclear extracts) and in vivo (in protoplasts). Next, genome-wide H3K9/14ac profiles in Arabidopsis seedlings were generated by chromatin immunoprecipitation sequencing, and changes induced by GSNO, GSNO/2-4-carboxyphenyl-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide or trichostatin A (an HDAC inhibitor) were quantified, thereby identifying genes that display putative NO-regulated histone acetylation. Functional classification of these genes revealed that many of them are involved in the plant defense response and the abiotic stress response. Furthermore, salicylic acid, which is the major plant defense hormone against biotrophic pathogens, inhibited HDAC activity and increased histone acetylation by inducing endogenous NO production. These data suggest that NO affects histone acetylation by targeting and inhibiting HDAC complexes, resulting in the hyperacetylation of specific genes. This mechanism might operate in the plant stress response by facilitating the stress-induced transcription of genes.

Nitric oxide production in plants: an update.

Nitric oxide (NO) is a key signaling molecule in plant physiology. However, its production in photosynthetic organisms remains partially unresolved. The best characterized NO production route involves the reduction of nitrite to NO via different non-enzymatic or enzymatic mechanisms. Nitrate reductases (NRs), the mitochondrial electron transport chain, and the new complex between NR and NOFNiR (nitric oxide-forming nitrite reductase) described in Chlamydomonas reinhardtii are the main enzymatic systems that perform this reductive NO production in plants. Apart from this reductive route, several reports acknowledge the possible existence of an oxidative NO production in an arginine-dependent pathway, similar to the nitric oxide synthase (NOS) activity present in animals. However, no NOS homologs have been found in the genome of embryophytes and, despite an increasing amount of evidence attesting to the existence of NOS-like activity in plants, the involved proteins remain to be identified. Here we review NO production in plants with emphasis on the presentation and discussion of recent data obtained in this field.

Large-Scale Phenomics Identifies Primary and Fine-Tuning Roles for CRKs in Responses Related to Oxidative Stress.

Cysteine-rich receptor-like kinases (CRKs) are transmembrane proteins characterized by the presence of two domains of unknown function 26 (DUF26) in their ectodomain. The CRKs form one of the largest groups of receptor-like protein kinases in plants, but their biological functions have so far remained largely uncharacterized. We conducted a large-scale phenotyping approach of a nearly complete crk T-DNA insertion line collection showing that CRKs control important aspects of plant development and stress adaptation in response to biotic and abiotic stimuli in a non-redundant fashion. In particular, the analysis of reactive oxygen species (ROS)-related stress responses, such as regulation of the stomatal aperture, suggests that CRKs participate in ROS/redox signalling and sensing. CRKs play general and fine-tuning roles in the regulation of stomatal closure induced by microbial and abiotic cues. Despite their great number and high similarity, large-scale phenotyping identified specific functions in diverse processes for many CRKs and indicated that CRK2 and CRK5 play predominant roles in growth regulation and stress adaptation, respectively. As a whole, the CRKs contribute to specificity in ROS signalling. Individual CRKs control distinct responses in an antagonistic fashion suggesting future potential for using CRKs in genetic approaches to improve plant performance and stress tolerance.

Production, amplification and systemic propagation of redox messengers in plants? The phloem can do it all!

Rapid long-distance signalling is an emerging topic in plant research, and is particularly associated with responses to biotic and abiotic stress. Systemic acquired resistance (SAR) to pathogen attack is dependent on nitric oxide (NO) and reactive oxygen species (ROS) such as hydrogen peroxide (H2 O2 ). By comparison, systemic wound responses (SWRs) and systemic acquired acclimation (SAA) to abiotic stress encounters are triggered by rapid waves of H2 O2 , calcium and electrical signalling. Efforts have been made to decipher the relationship between redox messengers, calcium and other known systemic defence signals. Less is known about possible routes of signal transduction throughout the entire plant. Previously, the phloem has been suggested to be a transport conduit for mobile signals inducing SAR, SWR and SAA. This review highlights the role of the phloem in systemic redox signalling by NO and ROS. A not yet identified calcium-dependent NO source and S-nitrosoglutathione reductase are candidate regulators of NO homeostasis in the phloem, whereas ROS concentrations are controlled by NADPH oxidases and the H2 O2 -scavenging enzyme ascorbate peroxidase. Possible amplification mechanisms in phloem-mediated systemic redox signalling are discussed.

Modulation of Protein S-Nitrosylation by Isoprene Emission in Poplar.

Researchers have been examining the biological function(s) of isoprene in isoprene-emitting (IE) species for two decades. There is overwhelming evidence that leaf-internal isoprene increases the thermotolerance of plants and protects them against oxidative stress, thus mitigating a wide range of abiotic stresses. However, the mechanisms of abiotic stress mitigation by isoprene are still under debate. Here, we assessed the impact of isoprene on the emission of nitric oxide (NO) and the S-nitroso-proteome of IE and non-isoprene-emitting (NE) gray poplar (Populus × canescens) after acute ozone fumigation. The short-term oxidative stress induced a rapid and strong emission of NO in NE compared with IE genotypes. Whereas IE and NE plants exhibited under nonstressful conditions only slight differences in their S-nitrosylation pattern, the in vivo S-nitroso-proteome of the NE genotype was more susceptible to ozone-induced changes compared with the IE plants. The results suggest that the nitrosative pressure (NO burst) is higher in NE plants, underlining the proposed molecular dialogue between isoprene and the free radical NO Proteins belonging to the photosynthetic light and dark reactions, the tricarboxylic acid cycle, protein metabolism, and redox regulation exhibited increased S-nitrosylation in NE samples compared with IE plants upon oxidative stress. Because the posttranslational modification of proteins via S-nitrosylation often impacts enzymatic activities, our data suggest that isoprene indirectly regulates the production of reactive oxygen species (ROS) via the control of the S-nitrosylation level of ROS-metabolizing enzymes, thus modulating the extent and velocity at which the ROS and NO signaling molecules are generated within a plant cell.

Nitric oxide-fixation by non-symbiotic haemoglobin proteins in Arabidopsis thaliana under N-limited conditions.

Nitric oxide (NO) is an important signalling molecule that is involved in many different physiological processes in plants. Here, we report about a NO-fixing mechanism in Arabidopsis, which allows the fixation of atmospheric NO into nitrogen metabolism. We fumigated Arabidopsis plants cultivated in soil or as hydroponic cultures during the whole growing period with up to 3 ppmv of NO gas. Transcriptomic, proteomic and metabolomic analyses were used to identify non-symbiotic haemoglobin proteins as key components of the NO-fixing process. Overexpressing non-symbiotic haemoglobin 1 or 2 genes resulted in fourfold higher nitrate levels in these plants compared with NO-treated wild-type. Correspondingly, rosettes size and weight, vegetative shoot thickness and seed yield were 25, 40, 30, and 50% higher, respectively, than in wild-type plants. Fumigation with 250 ppbv 15 NO confirmed the importance of non-symbiotic haemoglobin 1 and 2 for the NO-fixation pathway, and we calculated a daily uptake for non-symbiotic haemoglobin 2 overexpressing plants of 250 mg N/kg dry weight. This mechanism is probably important under conditions with limited N supply via the soil. Moreover, the plant-based NO uptake lowers the concentration of insanitary atmospheric NOx, and in this context, NO-fixation can be beneficial to air quality.

Copper amine oxidase 8 regulates arginine-dependent nitric oxide production in Arabidopsis thaliana.

Nitric oxide (NO) is a key signaling molecule in plants, regulating a wide range of physiological processes. However, its origin in plants remains unclear. It can be generated from nitrite through a reductive pathway, notably via the action of the nitrate reductase (NR), and evidence suggests an additional oxidative pathway, involving arginine. From an initial screen of potential Arabidopsis thaliana mutants impaired in NO production, we identified copper amine oxidase 8 (CuAO8). Two cuao8 mutant lines displayed a decreased NO production in seedlings after elicitor treatment and salt stress. The NR-dependent pathway was not responsible for the impaired NO production as no change in NR activity was found in the mutants. However, total arginase activity was strongly increased in cuao8 knockout mutants after salt stress. Moreover, NO production could be restored in the mutants by arginase inhibition or arginine addition. Furthermore, arginine supplementation reversed the root growth phenotype observed in the mutants. These results demonstrate that CuAO8 participates in NO production by influencing arginine availability through the modulation of arginase activity. The influence of CuAO8 on arginine-dependent NO synthesis suggests a new regulatory pathway for NO production in plants.

Common ragweed (Ambrosia artemisiifolia L.): allergenicity and molecular characterization of pollen after plant exposure to elevated NO2.

Ragweed pollen is the main cause of allergenic diseases in Northern America, and the weed has become a spreading neophyte in Europe. Climate change and air pollution are speculated to affect the allergenic potential of pollen. The objective of this study was to investigate the effects of NO2 , a major air pollutant, under controlled conditions, on the allergenicity of ragweed pollen. Ragweed was exposed to different levels of NO2 throughout the entire growing season, and its pollen further analysed. Spectroscopic analysis showed increased outer cell wall polymers and decreased amounts of pectin. Proteome studies using two-dimensional difference gel electrophoresis and liquid chromatography-tandem mass spectrometry indicated increased amounts of several Amb a 1 isoforms and of another allergen with great homology to enolase Hev b 9 from rubber tree. Analysis of protein S-nitrosylation identified nitrosylated proteins in pollen from both conditions, including Amb a 1 isoforms. However, elevated NO2 significantly enhanced the overall nitrosylation. Finally, we demonstrated increased overall pollen allergenicity by immunoblotting using ragweed antisera, showing a significantly higher allergenicity for Amb a 1. The data highlight a direct influence of elevated NO2 on the increased allergenicity of ragweed pollen and a direct correlation with an increased risk for human health.

Nitrite is the driver, phytohormones are modulators while NO and H2O2 act as promoters of NO2-induced cell death.

This study aimed to understand the molecular mechanisms of nitrogen dioxide (NO2)-induced toxicity and cell death in plants. Exposure of Arabidopsis to high concentrations of NO2 induced cell death in a dose-dependent manner. No leaf symptoms were visible after fumigation for 1 h with 10 parts per million (ppm) NO2 However, 20 ppm NO2 caused necrotic lesion formation and 30 ppm NO2 complete leaf collapse, which had already started during the 1 h fumigation period. NO2 fumigation resulted in a massive accumulation of nitrite and in protein modifications by S-nitrosylation and tyrosine nitration. Nitric oxide (NO) at 30 ppm did not trigger leaf damage or any of the effects observed after NO2 fumigation. The onset of NO2-induced cell death correlated with NO and hydrogen peroxide (H2O2) signaling and a decrease in antioxidants. NO- and H2O2-accumulating mutants were more sensitive to NO2 than wild-type plants. Accordingly, experiments with specific scavengers confirmed that NO and H2O2 are essential promoters of NO2-induced cell death. Leaf injection of 100 mM nitrite caused an increase in S-nitrosylation, NO, H2O2, and cell death suggesting that nitrite functioned as a mediator of NO2-induced effects. A targeted screening of phytohormone mutants revealed a protective role of salicylic acid (SA) signaling in response to NO2 It was also shown that phytohormones were modulators rather than inducers of NO2-induced cell death. The established experimental set-up is a suitable system to investigate NO2 and cell death signaling in large-scale mutant screens.

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.