Root Iron Research Articles

Small ARF-like 2 GTPase TITAN 5 is linked with the dynamic regulation of IRON-REGULATED TRANSPORTER 1.

Iron acquisition is crucial for plants. The abundance of IRON-REGULATED TRANSPORTER 1 (IRT1) is controlled through endomembrane trafficking, a process that requires small ARF-like GTPases. Only few components are known that are involved in the vesicular trafficking of specific cargo. Here, we report that the ARF-like GTPase TITAN 5 (TTN5) interacts with the large cytoplasmic variable region and protein-regulatory platform of IRT1. Heterozygous ttn5-1 plants can display a reduced activity of root iron reductase. This activity is needed for iron uptake via IRT1. Fluorescent fusion proteins of TTN5 and IRT1 colocalize at places, where IRT1 sorting and cycling between the plasma membrane and the vacuole are coordinated. TTN5 can also interact with peripheral membrane proteins that are components of the IRT1 regulation machinery, like the trafficking factor SNX1, the C2 domain protein EHB1 and the SEC14-GOLD protein PATL2. Hence, the link between iron acquisition and vesicular trafficking involving a small GTPase of the ARF family opens up the possibility to study the involvement of TTN5 in nutritional cell biology in the endomembrane system.

Differential Responses of Phenolics and Lignin Metabolism to Excess Iron and Zinc in Monocot and Dicot Roots Treated by Silicon

Differential Responses of Phenolics and Lignin Metabolism to Excess Iron and Zinc in Monocot and Dicot Roots Treated by Silicon

Efficiency of zinc in alleviating cadmium toxicity in hydroponically grown lettuce (Lactuca sativa L. cv. Ferdos)

BackgroundA study on photosynthetic and enzyme activity changes and mineral content in lettuce under cadmium stress has been conducted in a greenhouse, utilizing the modulated effect of zinc (Zn) application in the nutrient solution on lettuce. Zn is a micronutrient that plays an essential role in various critical plant processes. Accordingly, three concentrations of Zn (0.022, 5, and 10 mg L− 1) were applied to hydroponically grown lettuce (Lactuca sativa L. cv. Ferdos) under three concentrations of Cd toxicity (0, 2.5, and 5 mg L− 1).ResultsThe results showed that along with increasing concentrations of zinc in the nutrient solution, growth traits such as plant performance, chlorophyll index (SPAD), minimum fluorescence (F0), leaf zinc content (Zn), leaf and root iron (Fe) content, manganese (Mn), copper (Cu), and cadmium increased as well. The maximum amounts of chlorophyll a (33.9 mg g− 1FW), chlorophyll b (17.3 mg g− 1FW), carotenoids (10.7 mg g− 1FW), maximum fluorescence (Fm) (7.1), and variable fluorescence (Fv) (3.47) were observed in the treatment with Zn without Cd. Along with an increase in Cd concentration in the nutrient solution, the maximum amounts of leaf proline (5.93 mmol g− 1FW), malondialdehyde (MDA) (0.96 μm g− 1FW), hydrogen peroxide (H2O2) (22.1 μm g− 1FW), and superoxide dismutase (SOD) (90.3 Unit mg− 1 protein) were recorded in lettuce treated with 5 mg L− 1 of Cd without Zn. Additionally, the maximum activity of leaf guaiacol peroxidase (6.46 Unit mg− 1 protein) was obtained with the application of Cd at a 5 mg L− 1 concentration.ConclusionsIn general, an increase in Zn concentration in the nutrient solution decreased the absorption and toxicity of Cd in lettuce leaves, as demonstrated in most of the measured traits. These findings suggest that supplementing hydroponic nutrient solutions with zinc can mitigate the detrimental effects of cadmium toxicity on lettuce growth and physiological processes, offering a promising strategy to enhance crop productivity and food safety in cadmium-contaminated environments.

Response of selected scion and rootstock grape (<i>Vitis </i>spp.) genotypes to induced drought stress

Climate change is expected to elevate drought frequency, straining agricultural freshwater resources. Developing drought-tolerant grapevine varieties is crucial. This study examined grape scion and rootstock genotypes under well-watered (WW) and induced-drought (ID) conditions. ID treatment reduced vine length by 11.34-35.15%, with Vitis parviflora, 110R, and Male Hybrid rootstocks showing superior growth. Root length increased under ID, indicating an adaptive moisture-seeking response. The ID treatment led to substantial reduction in leaf count and average leaf area, especially in Flame Seedless (27.71 and 19.07 cm2, respectively). Drought stress elevated chlorophyll a:b ratio, affecting chlorophyll degradation in different genotypes. Significant variations were observed in leaf and root iron (Fe) and zinc (Zn) contents. Enzyme activities particularly peroxidase and polyphenol oxidase especially rose under drought, particularly in V. parviflora (3.39 μM guaiacol min-1 mg-1 protein and 1.33EU/ml/min respectively) likely to be contributing in drought tolerance mechanism. Principal component analysis (PCA) highlighted impact of traits on genotypes, emphasizing V. parviflora, Male Hybrid and Pusa Navrang as superior drought stress tolerant genotypes. Genotype clustering confirmed distinct groupings, while, correlation analysis unveiled intricate trait interactions.

High-efficiency remediation of Hg and Cd co-contaminated paddy soils by Fe–Mn oxide modified biochar and its microbial community responses

Fe–Mn oxide modified biochar (FMBC) was produced to explore its potential for remediation of Hg–Cd contaminated paddy soils. The results showed that the application of FMBC decreased the contents of bioavailable Hg and Cd by 41.49–81.85% and 19.47–33.02% in contrast to CK, while the amount of labile organic carbon (C) fractions and C-pool management index (CPMI) was increased under BC and FMBC treated soils, indicating the enhancement of soil C storage and nutrient cycling function. Dry weight of different parts of Oryza sativa L. was enhanced after the addition of BC and FMBC, and the contents of Fe and Mn in root iron–manganese plaques (IMP) were 1.46–2.06 and 6.72–19.35 times higher than those of the control groups. Hg and Cd contents in brown rice under the FMBC treatments were significantly reduced by 18.32–71.16% and 59.52–72.11% compared with the control. FMBC addition altered the composition and metabolism function of soil bacterial communities, especially increasing the abundance of keystone phyla, including Firmicutes, Proteobacteria and Actinobacteria. Partial least squares path modelling (PLSPM) revealed that the contents of Na2S2O3–Hg, DTPA–Cd and IMP were the key indicators affecting Hg and Cd accumulation in rice grains. These results demonstrate the simultaneous value of FMBC in remediation of Hg and Cd combined pollution and restoring soil fertility and biological productivity.Graphical

Safe production of rice in Cd-polluted paddy fields by rhizosphere application of zero-valent iron nanoplates at specific growth stages

Nanoscale zero-valent iron (nZVI) is efficient in immobilizing soil heavy metals for rice safe production, but is still limited in field application due to the relatively short effective duration and the required high dose. Herein, ball-milled ZVI nanoplates (10, 100, and 1000 mg kg−1) of ∼5 μm in width and ∼100 nm in thickness were injected into rice rhizosphere at different growth stages in three paddy fields with different Cd pollution levels (0.76–27.34 mg kg−1) to explore the optimum application time and dose for rice safe production. Although applying ZVI nanoplates at the pre-sowing, jointing, and flowering stages all promoted root iron plaque (IP) formation and Cd sequestration by IP, it could not prevent Cd accumulation in brown rice due to the later IP weathering and subsequent Cd remobilization. In contrast, the brown rice Cd content was significantly reduced to the safe level by the 100 and 1000 mg kg−1 ZVI nanoplate treatments at the grain-filling stage when the grain Cd accumulation occurs; moreover, the 100 mg kg−1 ZVI nanoplate treatment at this stage significantly increased the rice yield and thousand kernel weight, without adversely affecting soil microbial community. The findings provide a feasible nZVI application technique for safe production of rice in Cd-polluted paddy fields.

IMA peptides are dwarf giants fighting for fitness

IRON MAN (IMA) peptides have a critical role in iron uptake and homeostasis, but whether and how they associate with plant immunity signaling remain unclear. Recently, Cao et al. provided intriguing insights into the underlying plant mechanisms that restrict root iron acquisition on perception of microorganism-associated molecular patterns (MAMPs) by spatial IMA-1 turnover.

Selenium increases antimony uptake in ramie (Boehmeria nivea L.) by enhancing the physiological, antioxidative, and ionomic mechanisms

Ramie (Boehmeria nivea L.) is a promising phytoremediation candidate due to its high tolerance and enrichment capacity for antimony (Sb). However, challenges arise as Sb accumulated mainly in roots, complicating soil extraction. Under severe Sb contamination, the growth of ramie may be inhibited. Strategies are needed to enhance Sb accumulation in ramie's aboveground parts and improve tolerance to Sb stress. Considering the beneficial effects of selenium (Se) on plant growth and enhancing resistance to abiotic stresses, this study aimed to investigate the potential use of Se in enhancing Sb uptake by ramie. We investigated the effects of Se (0.5, 1, 2, 5, or 10 μM) on ramie growth, Sb uptake and speciation, antioxidant responses, and ionomic profiling in ramie under 10 mg/L of SbIII or antimonate (SbV) stresses. Results revealed that the addition of 0.5 μM Se significantly increased shoot biomass by 75.73% under SbIII stress but showed minimal effects on shoot and root length in both SbIII and SbV treatments. Under SbIII stress, 2 μM Se significantly enhanced Sb concentrations by 48.42% in roots and 62.88% in leaves. In the case of SbV exposure, 10 μM Se increased Sb content in roots by 42.57%, and 1 μM Se led to a 91.74% increase in leaves. The speciation analysis suggested that Se promoted the oxidation of SbIII to less toxic SbV to mitigate Sb toxicity. Additionally, Se addition effectively minimized the excess reactive oxygen species produced by Sb exposure, with the lowest malondialdehyde (MDA) content at 0.5 μM Se under SbIII and 2 μM Se under SbV, by activating antioxidant enzymes including superoxide dismutase, catalase, peroxidase, and glutathione peroxidase. Ionomic analysis revealed that Se helped in maintaining the homeostasis of certain nutrient elements, including magnesium, potassium (K), calcium (Ca), iron (Fe), and copper (Cu) in the SbIII-treated roots and K and manganese (Mg) in the SbV-treated roots. The results suggest that low concentrations of Se can be employed to enhance the phytoremediation of Sb-contaminated soils using ramie.

Contrasting roles of rice root iron plaque in retention and plant uptake of silicon, phosphorus, arsenic, and selenium in diverse paddy soils

Background and aimsIron (Fe) plaque on rice roots is a mixture of Fe oxide and oxyhydroxide minerals thought to protect rice from high levels of arsenic (As) in flooded paddy soils. Silicon (Si), phosphorus (P), and selenium (Se) also exist as oxyanions in rice paddies, but the impacts of Fe plaque on uptake of these nutrients are unknown.MethodsWe used natural variation in paddy soil chemistry to test how Si, P, As, and Se move from porewater to plaque to plant via multiple techniques. In a pot study, we monitored Fe plaque deposition and porewater chemistry in 5 different soils over time and measured plaque/plant chemistry and Fe plaque mineralogy at harvest. We normalized oxyanion concentrations by Fe to determine the preferential retention on plaque or plant uptake.ResultsLow phosphorus availability increased root Fe-oxidizing activity, while Fe, Si, P, As, and Se concentrations in plaque were strongly correlated with porewater. Plaque did not appreciably retain Si and Se, and the oxyanions did not compete for adsorption sites on the Fe plaque.ConclusionRoot Fe plaque seems to protect rice from As uptake, does not interfere with Si and Se uptake, and roots adapt to maintain P nutrition even with retention of porewater P on plaque.

Spatial IMA1 regulation restricts root iron acquisition on MAMP perception.

Iron is critical during host-microorganism interactions1-4. Restriction of available iron by the host during infection is an important defence strategy, described as nutritional immunity5. However, this poses a conundrum for externally facing, absorptive tissues such as the gut epithelium or the plant root epidermis that generate environments that favour iron bioavailability. For example, plant roots acquire iron mostly from the soil and, when iron deficient, increase iron availability through mechanisms that include rhizosphere acidification and secretion of iron chelators6-9. Yet, the elevated iron bioavailability would also be beneficial for the growth of bacteria that threaten plant health. Here we report that microorganism-associated molecular patterns such as flagellin lead to suppression of root iron acquisition through a localized degradation of the systemic iron-deficiency signalling peptide Iron Man 1 (IMA1) in Arabidopsis thaliana. This response is also elicited when bacteria enter root tissues, but not when they dwell on the outer root surface. IMA1 itself has a role in modulating immunity in root and shoot, affecting the levels of root colonization and the resistance to a bacterial foliar pathogen. Our findings reveal an adaptive molecular mechanism of nutritional immunity that affects iron bioavailability and uptake, as well as immune responses.

Using Biochar and Iron-calcium Material to Remediate Paddy Soil Contaminated by Cadmium and Arsenic

In this study, iron-calcium material (FC) and hickory-cattail biochar (BC) were applied to prepare composite material (BF), which was used to repair the combined pollution of cadmium and arsenic in paddy soil to reduce the content of cadmium (Cd) and arsenic (As) in rice grain. Soil pore water, rhizosphere soil, bulk soil, rice plants, and root iron plaque samples were collected during the growth period of rice in a pot experiment to explore the effects and mechanism of FC, BC, and BF on the bioavailability of Cd and As in paddy soil and their contents in plants. The results showed that biochar could significantly (P < 0.05) increase the pH value of bulk soil (0.55-0.66 units) and rhizosphere soil (0.28-0.36 units) and elevate the soil dissolved organic carbon (DOC) content. FC material could significantly (P < 0.05) reduce the pH of bulk soil (0.14-0.27 units) and rhizosphere soil (0.38-0.41 units), as well as the soil DOC content. Iron-calcium materials and composite could simultaneously reduce the contents of available Cd and As in soil pore water, rhizosphere soil, and bulk soil, whereas biochar could reduce the content of Cd but increase the content of As. Among them, a 1% addition of composite had the best effect. The available Cd and As in soil decreased by 41.8%-48.2% and 6.1%-10.1%, respectively. Biochar, iron-calcium materials, and composites improved plant biomass (dry weight of root, stem, leaf, and grain). For example, the dry weights of rice grains under these treatments were higher (48.5%-184.0%) than that of CK, as was the root iron plaque content (7.5%-13.6%). Compared with that in the CK, biochar could effectively reduce the Cd content in rice grain by 21.0%-26.1%. Iron-calcium material and composite could simultaneously reduce the Cd and As contents in rice grain. Among them, the BF treatment had the best effect on the reduction of Cd and As in rice grain, with a decrease of 36.9%-42.0% and 40.4%-44.4%, respectively. The Cd and As contents in rice grain were lower than the national standard values (GB 2762-2017).

The impact of rainwater-borne H2O2-induced Fenton process on root iron plaque formation and arsenic accumulation in rice

Arsenic (As) contamination is a global concern, especially in paddy fields, as it represents a significant pathway for As reaching in the food chain. This is primarily due to the high accumulation of As in rice grains, which is a staple food for billions of people globally. Here we investigated the effect of synthetic rainwater-borne hydrogen peroxide (H2O2)-induced Fenton oxidation process in paddy soil on As uptake and speciation in rice plants at different growth stages. Results showed that adding Fenton reagents significantly accelerated root iron (Fe) plaque formation, thereby enhancing As retention in soil. Arsenic accumulation in different rice plant parts followed the order: Fe plaque > root > stem > leaf. In rice grains, inorganic As and dimethylarsinic acid (DMA) were the major As species for the first and second-season crops. Notably, that the addition of Fenton reagents to paddy soil led to a significant reduction in As accumulation in rice grains. The synthetic rainwater-borne H2O2-induced Fenton reaction significantly promoted As(V) precipitation and decreased concentration of the dissolved As in soil porewater. The current study highlights that the H2O2-induced Fenton process is an important pathway decreasing As bioavailability in paddy soil and its accumulation in rice grain. The findings have implications for understanding As behavior in paddy fields receiving rainwater-borne H2O2 and for developing cost-effective remediation programs to reduce As accumulation in rice grains.

Plant commensal type VII secretion system causes iron leakage from roots to promote colonization.

Competition for iron is an important factor for microbial niche establishment in the rhizosphere. Pathogenic and beneficial symbiotic bacteria use various secretion systems to interact with their hosts and acquire limited resources from the environment. Bacillus spp. are important plant commensals that encode a type VII secretion system (T7SS). However, the function of this secretion system in rhizobacteria-plant interactions is unclear. Here we use the beneficial rhizobacterium Bacillus velezensis SQR9 to show that the T7SS and the major secreted protein YukE are critical for root colonization. In planta experiments and liposome-based experiments demonstrate that secreted YukE inserts into the plant plasma membrane and causes root iron leakage in the early stage of inoculation. The increased availability of iron promotes root colonization by SQR9. Overall, our work reveals a previously undescribed role of the T7SS in a beneficial rhizobacterium to promote colonization and thus plant-microbe interactions.

Effect of calcium and trace metals (Cd, Cu, Mn, Ni, Zn) on root iron uptake in relation to chemical properties of the root-excreted ligands.

Interferences of major cations (Ca2+, Mg2+) and trace metals (TM, i.e. Cd2+, Cu2+, Mn2+, Ni2+ and Zn2+) in root Fe uptakewere evaluated. Root Fe uptake was modelled including the reactions of the root exuded ligand with the soil major and trace cations. Fe uptake was simulated with different ligands representing various affinities for the cations, the latter varying in concentration. The stability constant of Fe complexes (KFeL) does not influence Fe uptake, contrarily to the ligand parameters for Fe-hydroxide dissolution. Fe uptake decreases when KCaL or Ca2+ in solution increases. Presence of TM has nearly no influence on Fe uptake when the TM complexes have low stability constants (KML), as in the case of oxalate and citrate complexes. When ligands have high KML, like EDTA, DFO-B or mugineic acid (MA), TM reduces Fe uptake by 51-55%, and much more in the case of TM contamination. Exudation of Fe ligands with low KML has no negative effect on TM uptake, which can increase if the dissociation rate is high, as for Cu complexes. Ligands with high KML (EDTA, DFO-B, MA) greatly reduce TM uptake, only if their hydrated cations can be absorbed. Calcium does not significantly reduce Fe uptake when Ca-complexes have KCaL < 104. Consequently, ligands like oxalate or MA should be efficient in most soils. TM should perturbate Fe uptake mediated by ligands with high KML such as MA, but not oxalate. Plants exuding phytosiderophores should also absorb TM complexes to avoid micronutrient deficiencies.

Mineralogical characteristics of root iron plaque and its functional mechanism for regulating Cr phytoextraction of hyperaccumulator Leersia hexandra Swartz

Leersia hexandra Swartz (L. hexandra) is a promising hyperaccumulator for Cr pollution remediation, but whether its Cr phytoextraction is subject to the root surface-attached iron plaque (IP) remains unclear. In this research, the natural and artificial IPs were proven to be comprised of small amounts of exchangeable Fe as well as carbonate Fe, and dominantly Fe minerals involving amorphous two-line ferrihydrite (Fh), poorly crystalline lepidocrocite (Le) and highly crystalline goethite (Go). The Fe content in the artificial IPs augmented with increasing induced Fe(II) concentration, and the 50 mg/L Fe(II) led to the identical Fe content and different component proportions of artificial IP (Fe50) and natural IP. Fh was consisted of highly aggregated nanoparticles, and the aging of Fh caused its phase conversion to rod-like Le and Go. The Cr(VI) adsorption results of Fe minerals corroborated the coordination of Cr(VI) onto the Fh surface and the significantly greater equilibrium Cr(VI) adsorption amount of Fh over Le and Go. The greatest Cr(VI) reduction capacity of Fh among three Fe minerals was found to be related to its most abundant surface-adsorbed Fe(II) content. The results of hydroponic experiment of L. hexandra showed that the presence of IP facilitated the Cr(VI) removal by L. hexandra during the cultivation period of 10–45 days, and consequently, compared to the Fe0 group (without IP), around 60% of increase in the Cr accumulation of shoots was achieved by Fe50 group. The findings of this work are conductive to furthering our understanding of IP-regulated Cr phytoextraction of L. hexandra.

Oxygen Nanobubble-Loaded Biochars Mitigate Copper Transfer from Copper-Contaminated Soil to Rice and Improve Rice Growth

Copper (Cu)-contaminated paddy soil has caused substantial concerns for human health through biomagnification in the soil–rice–human chain. In this study, oxygen nanobubble-loaded biochars (ONBC), including pyrochars (NPC) and hydrochars (NHC), were used to amend Cu-contaminated paddy soils and reduce rice Cu toxicity. The ONBC amendment improved the rhizospheric redox potential and dissolved oxygen concentration via slow, continuous oxygen release, promoting root iron plaque formation and effectively inhibiting root Cu influx. Moreover, the ONBC amendment improved soil microbial diversity. The abundance of bacterial genes involved in cytosolic Cu complexation and Cu export to the periplasm space for Cu stabilization markedly improved. The sequestered Cu in root iron plaque and soil bacteria inhibited Cu influx into the shoots to avoid Cu overaccumulation in the edible parts. This was reflected by the Cu content decreasing by 1.91-fold and 2.38-fold in shoots under NPC and NHC treatments, respectively. Furthermore, the improved oxygen-enriched rhizosphere environment via the ONBC amendment promoted root activity and the abundance of bacterial genes involved in nutrients mineralization, further promoting shoot biomass by 1.46-fold and 2.29-fold under NPC and NHC treatments, respectively. This study proposes an environmentally friendly strategy to mitigate Cu transfer from soil to crops and improve crop productivity.

The effect of the chelated form of iron on its mobility and phytodavailability when applied to the soil

In spite of well-known mechanisms of iron consumption by plants from the soil and action patterns of iron ions in the soils, the work to eliminate the deficiency of this trace element in plants is still relevant. The article presents an assessment of the effect of iron (III) chelate complexes with diethylenetriaminepentaacetic acid (DTPА Fe) and ethylenediaminetetraacetic acid (EDTA Fe) on the mobility and availability of iron for plants in soil with a pH close to neutral. In a model experiment with using of drainage columns, there were established the patterns of iron distribution in the soil and its removal with irrigation water from the root zone of plants (10 cm). Against the background of similar distribution of iron in the soil, a higher content of its mobile forms in the lower layers was noted when using EDTA Fe. The leaching of iron from the soil was confirmed using both DTPA Fe and EDTA Fe. The vegetation experiment revealed the effect of chelate forms on the accumulation of iron in barley plants (Hordeum vulgare L.) during their early growth period (11 days). The iron content in the shoots varied from 120 to 140 µg/g, in the roots – from 233 to 244 µg/g, with a content of 200 µg/g in the control sample. A significant contribution to the accumulation of iron in barley seedlings was observed at the level of the root system in the experiment with EDTA Fe. Data on the accumulation of iron in barley roots were correlated (r = 0.99) with data on their ash content.

Levels of elements in selected food substances that support usage in the management and treatment of erectile dysfunction.

The use of fruits and vegetables for the management and treatment of erectile dysfunction has gained popularity due to the cheaper cost, accessibility and perceived absence of side effects. Much of the work done on plant-based aphrodisiacs has focused on the phytochemistry of secondary metabolites. This work sought to analyze selected fruits and vegetables that are commonly used in the management of erectile dysfunction in Ghana and quantify the levels of some micro- and macro-elements necessary for good penile health in order to determine the usefulness or otherwise of the selected produce. Energy-dispersive X-ray fluorescence spectroscopy was used to detect and quantify the levels of potassium (K), calcium (Ca), selenium (Se), magnesium (Mg), iron (Fe), and zinc (Zn) in carrot roots, cucumber fruit, garlic bulb, ginger rhizome, nutmeg fruit, sweet potato tuber, tiger nut tuber and watermelon fruit. The analysis revealed the presence of K, Ca, Mg, Fe and Zn. Levels of Se were below detection. The concentration of K was the highest in each of the food substances. However, in terms of recommended daily allowance, Mg had the highest contribution. Cucumber fruit and the rind of watermelon fruit had the highest levels of micro- and macro-elements implicated in erectile dysfunction. The potential use of these foods to treat and manage erectile dysfunction may not only be due to the presence of phytochemicals alone but also the presence of significant levels of micro- and macro-elements required for good penile health.

Genome-wide transcriptome analysis of the orphan crop tef (Eragrostis tef (Zucc.) Trotter) under long-term low calcium stress

Calcium (Ca2+) is one of the essential mineral nutrients for plant growth and development. However, the effects of long-term Ca2+ deficiency in orphan crops such as Tef [(Eragrostis tef) (Zucc.) Trotter], which accumulate high levels of Ca in the grains, remained unknown. Tef is a staple crop for nearly 70 million people in East Africa, particularly in Ethiopia and Eritrea. It is one of the most nutrient-dense grains, and is also more resistant to marginal soils and climatic conditions than main cereals like corn, wheat, and rice. In this study, tef plants were grown in a hydroponic solution containing optimum (1 mM) or low (0.01 mM) Ca2+, and plant growth parameters and whole-genome transcriptome were analyzed. Ca+2-deficient plants exhibited leaf necrosis, leaf curling, and growth stunting symptoms. Ca2+ deficiency significantly decreased root and shoot Ca, potassium (K), and copper content in both root and shoots. At the same time, it greatly increased root iron (Fe) content, suggesting the role of Ca2+ in the uptake and/or translocation of these minerals. Transcriptomic analysis using RNA-seq revealed that members of Ca2+ channels, including the cyclic nucleotide-gated channels and glutamate receptor-like channels, Ca2+-transporters, Ca2+-binding proteins and Ca2+-dependent protein kinases were differentially regulated by Ca+2 treatment. Moreover, several Fe/metal transporters, including members of vacuolar Fe transporters, yellow stripe-like, natural resistance-associated macrophage protein, and oligo-peptide transporters, were differentially regulated between shoot and root in response to Ca2+ treatment. Taken together, our findings suggest that Ca2+ deficiency affects plant growth and mineral accumulation by regulating the transcriptomes of several transporters and signaling genes.

Differential metal sensing and metal-dependent degradation of the broad spectrum root metal transporter IRT1.

Iron is an essential micronutrient for plant growth and development. Under low iron conditions, Arabidopsis plants take up soil iron using the root iron transporter IRT1. In addition to iron, IRT1 also transports others divalent metals, including cadmium, which consequently accumulates into plant tissues and enters the food chain. IRT1 expression was shown to be regulated at the transcriptional and post-translational levels by its essential metal substrates to maximize iron uptake while limiting the accumulation of zinc, manganese, or cobalt. Here, we characterized the regulation of IRT1 by cadmium. A short-term exposure to cadmium decreased the cell surface levels of IRT1 through endocytosis and degradation, but with a lower efficiency than observed for other IRT1 metal substrates. We demonstrated that IRT1 endocytosis in response to cadmium is mediated through the direct binding of cadmium to histidine residues within the regulatory loop of IRT1. However, we revealed that the affinity of the metal sensing motif is much lower for cadmium compared to other metal substrates of IRT1. Finally, we proved that cadmium-induced IRT1 degradation takes place through ubiquitin-mediated endocytosis driven by the UBC35/36 E2 ubiquitin-conjugating enzymes and the IDF1 E3 ubiquitin ligase. Altogether, this work sheds light on the mechanisms of cadmium-mediated downregulation of IRT1 and provides an additional molecular basis for cadmium accumulation and toxicity in plants.