Fe-deficient Conditions Research Articles

A fungal endophyte increases plant resilience to low nutrient availabilities: a case of Fe acquisition in legumes.

Microbial inocula are considered a promising and effective alternative solution to the use of chemical fertilizers to support plant growth and productivity since they play a key role in the availability and uptake of nutrients. Here, the effect of a beneficial of a fungal root endophyte, Fusarium solani strain K (FsK), on nutrient acquisition efficiency of the legume Lotus japonicus was studied, and putative mode-of-action of the endophyte at a molecular level was determined. Plant colonization with the endophyte resulted in increased shoot and root fresh weight under Fe deficiency compared to control nutrient conditions. Plant inoculation with FsK was associated with a significant increase in macro- and micronutrient concentration in leaves at an early stage of endophyte inoculation and a replenishment of Fe content under prolonged iron starvation. The mechanistic basis of the plant growth promotion capabilities of the endophyte is exerted at the transcriptional level since we recorded changes in the expression levels of genes related to iron uptake in FsK-colonized plants under stress conditions compared to uninoculated plants. In addition, the observed changes in the ethylene biosynthesis-related genes suggest a possible implication of ethylene in the mode of action used by FsK to enhance plant response to nutrient stress conditions. Finally, we demonstrated that the endophyte possesses a reductive high-affinity Fe uptake system and identified a ferric reductase that was induced in planta under Fe deficiency conditions, indicating that this fungal Fe homeostasis mechanism may result in a benefit in nutrient acquisition for the plant as well.

Cultivating resilience: Harnessing pyoverdine-producing Pseudomonas to contrast iron deficiency in cucumber plants

Iron (Fe) deficiency in crops significantly reduces yield, impacting agricultural productivity worldwide. Synthetic Fe chelates are commonly applied as fertilizers to address this issue, but their synthetic nature and prolonged use poses environmental risks. Thus, inoculation of plant growth-promoting bacteria rises as an alternative to enhance Fe uptake in crops while minimizing reliance on synthetic chelates. This study aimed to examine the influence of Pseudomonas RMC4 inoculation and pyoverdine application on cucumber plants cultivated hydroponically under Fe deficiency conditions. Evaluations included the SPAD index, plant biomass, root morphology, Fe-chelate reductase activity, gene expression, and ionomic analysis. Following Fe deficiency, Pseudomonas RMC4 inoculation improved the SPAD index, increased dry weight, enhanced root development, and facilitated Fe acquisition mechanisms, thus, fostering the endogenous resilience of the plant to the limited Fe availability. This improvement was observed with bacterial inoculation or pyoverdine application alongside an insoluble Fe source (ferrihydrite). Overall, the results suggest the beneficial impact of Pseudomonas RMC4 inoculation in alleviating symptoms of Fe deficiency. Future studies will investigate bacterial application under field conditions to assess its potential in replacing synthetic Fe-chelates fertilizers in crop production in favor of more sustainable agriculture.

The phytosiderophore analogue proline-2′-deoxymugineic acid is more efficient than conventional chelators for improving iron nutrition in maize

ABSTRACT Iron (Fe) is an essential nutrient but has poor bioavailability because of its low solubility under conditions of high pH, such as calcareous soils. Previously, we synthesized an analogue of the natural Fe(III) chelator 2′-deoxymugineic acid secreted by graminaceous plants for efficient Fe uptake, designated as proline-2′-deoxymugineic acid (PDMA). Soil application of Fe(III)-PDMA ameliorated symptoms of Fe deficiency in rice. In the present study, we explored the potential of PDMA as Fe nutrition supplement in maize, a major graminaceous crop, and rice for comparison. In calcareous soil pots, Fe deficiency chlorosis of maize was efficiently recovered by a single application of Fe(III)-PDMA. In contrast, maize plants treated with conventional Fe(III)-chelator complexes, such as Fe(III)-ethylenediaminetetraacetic acid (EDTA) or Fe(III)-N,N′-di(2-hydroxybenzyl)ethylenediamine-N,N′-diacetic acid monohydrochloride (HBED), showed little or no recovery. Similarly, rice Fe chlorosis in calcareous soil pots was efficiently recovered by a single application of Fe(III)-PDMA, but not by other conventional Fe(III)-chelator complexes. Application of Fe(III)-PDMA was also effective in ameliorating Fe deficiency chlorosis in hydroponically grown maize seedlings; other Fe(III)-chelator complexes showed minimal or no efficacy. Addition of low concentrations of metal-free PDMA recovered Fe chlorosis of maize or rice in the presence of Fe(III)-EDTA, suggesting possible ligand exchange from EDTA to PDMA for subsequent Fe(III)-PDMA uptake by ZmYS1 and OsYSL15 transporters. Similar effects were observed with Fe(III)-HBED, which has a higher stability constant, but to a lesser extent than Fe(III)-EDTA, suggesting that ligand exchange from HBED to PDMA might be less prone to occur than for chelators with moderate stability constants, such as EDTA. Ferric-chelate reductase assays of maize roots showed substantial reduction of Fe(III)-PDMA, but this reduction activity was not increased under Fe-deficient condition. These results suggested that PDMA is an efficient reagent for improvement of Fe nutrition in graminaceous crops, including maize, because of suitability of Fe(III)-PDMA as a substrate for chelation-based Fe uptake systems.

NtZIP5A/B is involved in the regulation of Zn/Cu/Fe/Mn/Cd homeostasis in tobacco.

Plants grow in soils with varying concentrations of microelements, often in the presence of toxic metals e.g. Cd. To cope, they developed molecular mechanisms to regulate metal cross-homeostasis. Understanding underlying complex relationships is key to improving crop productivity. Recent research suggests that the Zn and Cd uptake protein NtZIP5A/B [Zinc-regulated, Iron-regulated transporter-like Proteins (ZIPs)] from tobacco (Nicotiana tabacum L. v. Xanthi) is involved in the regulation of a cross-talk between the two metals. Here, we support this conclusion by showing that RNAi-mediated silencing of NtZIP5A/B resulted in a reduction of Zn accumulation and that this effect was significantly enhanced by the presence of Cd. Our data also point to involvement of NtZIP5B in regulating a cross-talk between Cu, Fe, and Mn. Using yeast growth assays, Cu (but not Fe or Mn) was identified as a substrate for NtZIP5B. Furthermore, GUS-based analysis showed that the tissue-specific activity of the NtZIP5B promoter was different in each of the Zn-/Cu-/Fe-/Mn deficiencies applied with/without Cd. The results indicate that NtZIP5B is involved in maintaining multi-metal homeostasis under conditions of Zn, Cu, Fe, and Mn deficiency, and also in the presence of Cd. It was concluded that the protein regulates the delivery of Zn and Cu specifically to targeted different root cells depending on the Zn/Cu/Fe/Mn status. Importantly, in the presence of Cd, the activity of the NtZIP5B promoter is lost in meristematic cells and increased in mature root cortex cells, which can be considered a manifestation of a defense mechanism against its toxic effects.

Iron (Fe) Nutrient Dynamics in Oil Palm Leaves

Iron (Fe) management is crucial in cultivating oil palm, especially in sandy soils, due to its essential role in supporting photosynthesis and palm metabolism, directly influencing the quality and productivity of oil palms. This study aimed to explore the dynamics of Fe deficiency in oil palm leaves in Central Kalimantan, Indonesia. Using a Split Plot Design, the study compared plant conditions between the control (T0) and three levels of Fe deficiency: low (T1), moderate (T2), and severe (T3). Palm samples were selected using the purposive sampling method. Laboratory analysis of leaf samples indicated a significant decrease in Fe content in deficient palms, with levels of 41.49 µg/g in T1, 42.59 µg/g in T2, and 38.93 µg/g in T3, compared to the control group, which had 67.25 µg/g. The study also revealed that Fe deficiency affects the absorption of other macro and micronutrients. For instance, nitrogen levels increased under moderate Fe deficiency (2.57%), while potassium levels decreased (0.729%) at the same level. Despite the Fe deficiency, the plants adapted by maintaining other nutrient levels within a moderate range. Under severe Fe deficiency conditions, Cu levels reached their highest (5.868 µg/g), while Fe showed a significant decrease. This confirms that oil palm has complex nutrient adaptation and regulation mechanisms to maintain nutrient balance even under deficient conditions. These results emphasize the importance of Fe management in oil palm plantations, especially in sandy soils that are prone to nutrient deficiency.

Apo-siderophores promote growth of iron-deficient Arabidopsis plants by mobilizing iron from roots to shoots and reducing oxidative stress in roots

Iron (Fe) is an essential micronutrient for most organisms that is, however, poorly bioavailable in the soil. Acquiring this element is therefore a major issue for both plants and microorganisms. Bacteria acquire Fe by secreting siderophores that chelate the ferric ion with a high affinity and that can contribute to Fe nutrition in plants, under certain conditions including stressful ones. Our previous work has shown that pyoverdine, a siderophore purified from a beneficial Pseudomonas sp., leads to plant growth stimulation when supplied in its Fe-free form (apo-pyoverdine/apopyo) to Arabidopsis thaliana plants grown hydroponically under Fe-deficient conditions. To better understand siderophore-mediated growth promotion, we studied the impact of an apo-siderophore with a different structure from pyoverdine, deferoxamine (DFO), on the same model. Here we show that growth stimulation is linked to the ability of siderophores to chelate Fe, as DFO also promotes growth after 3 to 6 days when provided at 25 µM to 4-week-old A. thaliana plants starved for Fe for 1 to 7 days. The extent to which the siderophore stimulates root and shoot growth depends on the amount of Fe stored in the roots prior to the addition of DFO, and likely involves the remobilization of Fe from the roots to the shoots. The promotion of root growth by DFO does not appear to depend on coumarin production or secretion, but is associated with an increase in the expression of genes of the HOMOLOG OF BEE2 INTERACTING WITH IBH1 (HBI1)-dependent brassinosteroid signaling pathway. DFO stimulates lateral root elongation concomitant with a significant decrease in hydrogen peroxide (H2O2) and oxidized glutathione levels and a decrease in stress-related gene expression in roots. In addition, DFO decreases the expression of the UPBEAT (UPB1) gene involved in H2O2-mediated root growth inhibition, and thus lifts the inhibition of the expression of its target genes, the class III peroxidases that stimulate root growth. Overall, this work indicates that growth promotion by apo-siderophores in an iron-poor environment is likely linked to their ability to induce a stronger response to Fe deficiency while decreasing oxidative stress in roots, thus stimulating Fe remobilization from root Fe pools to shoots and promoting secondary root growth.

The activation of iron deficiency responses of grapevine rootstocks is dependent to the availability of the nitrogen forms

BackgroundIn viticulture, iron (Fe) chlorosis is a common abiotic stress that impairs plant development and leads to yield and quality losses. Under low availability of the metal, the applied N form (nitrate and ammonium) can play a role in promoting or mitigating Fe deficiency stresses. However, the processes involved are not clear in grapevine. Therefore, the aim of this study was to investigate the response of two grapevine rootstocks to the interaction between N forms and Fe uptake. This process was evaluated in a hydroponic experiment using two ungrafted grapevine rootstocks Fercal (Vitis berlandieri x V. vinifera) tolerant to deficiency induced Fe chlorosis and Couderc 3309 (V. riparia x V. rupestris) susceptible to deficiency induced Fe chlorosis.ResultsThe results could differentiate Fe deficiency effects, N-forms effects, and rootstock effects. Interveinal chlorosis of young leaves appeared earlier on 3309 C from the second week of treatment with NO3−/NH4+ (1:0)/-Fe, while Fercal leaves showed less severe symptoms after four weeks of treatment, corresponding to decreased chlorophyll concentrations lowered by 75% in 3309 C and 57% in Fercal. Ferric chelate reductase (FCR) activity was by trend enhanced under Fe deficiency in Fercal with both N combinations, whereas 3309 C showed an increase in FCR activity under Fe deficiency only with NO3−/NH4+ (1:1) treatment. With the transcriptome analysis, Gene Ontology (GO) revealed multiple biological processes and molecular functions that were significantly regulated in grapevine rootstocks under Fe-deficient conditions, with more genes regulated in Fercal responses, especially when both forms of N were supplied. Furthermore, the expression of genes involved in the auxin and abscisic acid metabolic pathways was markedly increased by the equal supply of both forms of N under Fe deficiency conditions. In addition, changes in the expression of genes related to Fe uptake, regulation, and transport reflected the different responses of the two grapevine rootstocks to different N forms.ConclusionsResults show a clear contribution of N forms to the response of the two grapevine rootstocks under Fe deficiency, highlighting the importance of providing both N forms (nitrate and ammonium) in an appropriate ratio in order to ease the rootstock responses to Fe deficiency.

Barley preferentially activates strategy-II iron uptake mechanism under iron deficiency

Plants utilize two main strategies for iron (Fe) uptake from the rhizosphere. Strategy-I is based on the reduction of ferric (Fe3+) to ferrous (Fe2+) iron by ferric chelate reductase (FCR) and is mainly observed in dicots. Strategy-II utilizes the complexation of Fe3+ with phytosiderophores secreted from the plant roots and mainly evolved in Gramineous species, including barley (Hordeum vulgare). Recent studies suggest that some species use a combination of both strategies for more efficient Fe uptake. However, the preference of barley for these strategies is not well understood. This study investigated the physiological and biochemical responses of barley under iron deficiency and examined the expression levels of the genes involved in Strategy-I and Strategy-II mechanisms in the roots. Fe deficiency led to decreased root and shoot lengths, fresh and dry weights, and Fe accumulation in the roots. Parallel to the chlorosis observed in the leaves, FCR activity and rhizosphere acidification were also significantly reduced in the roots, while the release of phytosiderophores increased. Furthermore, Strategy-II genes expressed higher than the Strategy-I genes in the roots under Fe deficiency. These findings demonstrate that Strategy-II is more activated than Strategy-I for Fe uptake in barley roots under Fe-deficient conditions.

Fe(III) transporter OsYSL15 may play a key role in the uptake of Cr(III) in rice (Oryza sativa L.)

Due to the widely discharge of chromium (Cr) by mining and smelting industries, etc., contamination of paddy soils and rice has become serious problems. Therefore it is crucial to explore how rice takes up Cr. Cr(III) is the most common Cr form in the long-term water flooding paddy soils. Here, we demonstrate that OsYSL15, a key gene for Fe(III) uptake, is equally applicable for Cr(III) uptake in rice. Firstly, the antagonistic effect of Cr(III) and Fe(III) in the uptake process was found. Rice could accumulate more Cr(III) under Fe-deficient conditions. And the Fe(III) content in the protoplasts of rice root cells gradually decreased with the increase exposure of Cr(III). Knockdown of OsYSL15 in rice significantly reduced the Cr(III) uptake rate. Compared with wild type rice, the accumulation of Cr(III) in OsYSL15 mutant was decreased by 40.7%− 70.6% after gene editing. These results indicate that OsYSL15 is a key gene responsible for Cr(III) uptake in rice, which can guide the screening or genetic modification for low-Cr-accumulation rice varieties.

Transcriptome and biochemical analysis in hexaploid wheat with contrasting tolerance to iron deficiency pinpoints multi-layered molecular process

Iron (Fe) is an essential plant nutrient that is indispensable for many physiological activities. This study is an effort to identify the molecular and biochemical basis of wheat genotypes with contrasting tolerance towards Fe deficiency. Our physiological experiments performed at the early growth stage in cv. Kanchan (KAN) showed Fe deficiency tolerance, whereas cv. PBW343 (PBW) was susceptible. Under Fe deficient condition, KAN showed delayed chlorosis, high SPAD values, and low malondialdehyde content compared to PBW, indicative of Fe deficient condition. Comparative shoot transcriptomics revealed increased expression of photosynthetic pathway genes in PBW, further suggesting its sensitivity to Fe fluctuations. Under Fe deficiency, both the cultivars showed distinct molecular re-arrangements such as high expression of genes involved in Fe uptake (including membrane transporters) and its remobilization. Specifically, in KAN these changes lead to high root phytosiderophores (PS) biosynthesis and its release, resulting in enhanced Fe translocation index. Utilizing the non-transgenic TILLING (Targeting Induced Lesions in Genomes) technology, we identified TaZIFL4.2D as a putative PS efflux transporter. Characterization of the wheat TILLING lines indicated that TaZIFL4.2 functions in PS release and Fe acquisition, thereby imparting tolerance to Fe deficiency. Altogether, this work highlights the mechanistic insight into Fe deficiency tolerance of hexaploid wheat, thus enabling breeders to select suitable genotypes to utilize nutrients for maximum yields.

Iron biofortification and yield of wheat grain in response to Fe fertilization and its driving variables: A meta-analysis

Iron (Fe) is an essential micronutrient for human nutrition and health, but its deficiency is prevalent worldwide. Wheat biofortification offers a potential strategy to alleviate micronutrient deficiencies in humans. However, the effects of Fe fertilization on grain Fe concentration and yield of wheat remain inconsistent. A global meta-analysis of 107 publications including 171 records of grain Fe concentration and 378 records of yield was conducted to quantify the contribution of Fe fertilization to wheat biofortification. Overall, compared with no Fe addition, Fe application significantly increased grain Fe concentration by 20.5% and yield by 12.4%. Foliar and soil application of Fe fertilizer increased grain Fe concentration by 18.2% and 26.7%, and grain yield by 15.1% and 9.5%, respectively. Results showed that higher foliar Fe fertilizer rate (>0.1%) and multiple applications before the flowering stage had a stronger effect on grain Fe concentration than lower Fe fertilizer rate (<0.1%) and only one application after flowering stage. Under severe soil Fe deficiency conditions (DTPA-Fe < 6 mg kg−1), the foliar application increased yield by 13.9%, more than the yield increase (4.0%) when soil DTPA-Fe was greater than 6 mg kg−1. Soil application of Fe was more effective to improve yield and grain Fe of wheat grown on high pH soil with lower available Fe. Furthermore, there was a positive relationship between the increase in the wheat grain yield and the increase in grain Fe concentration. In summary, our findings indicate that Fe fertilization can be managed in ways that simultaneously enhance grain nutritional quality and achieve high wheat yields.

Stimulating and toxic effect of chromium on growth and photosynthesis of a marine chlorophyte.

Marine phytoplankton can interchange trace metals in various biochemical functions, particularly under metal-limiting conditions. Here, we investigate the stimulating and toxicity effect of chromium (Cr) on a marine Chlorophyceae Osetreococcus tauri under Fe-replete and Fe-deficient conditions. We determined the growth, photosynthesis, and proteome expressions of Osetreococcus tauri cultured under different Cr and Fe concentrations. In Fe-replete conditions, the presence of Cr(VI) stimulated significantly the growth rate and the maximum yield of photochemistry of photosystem II (Fv /Fm ) of the phytoplankton, while the functional absorption cross-section of photosystem II (σPSII ) did not change. Minor additions of Cr(VI) partially rescued phytoplankton growth under Fe-limited conditions. Proteomic analysis of this alga grown in Fe-replete normal and Fe-replete with Cr addition media (10 μM Cr) showed that the presence of Cr significantly decreased the expression of phosphate-transporting proteins and photosynthetic proteins, while increasing the expression of proteins related to carbon assimilation. Cr can stimulate the growth and photosynthesis of O. tauri, but the effects are dependent on both the Cr(VI) concentration and the availability of Fe. The proteomic results further suggest that Cr(VI) addition might significantly increase starch production and carbon fixation.

Role of transcription factor complex OsbHLH156-OsIRO2 in regulating manganese, copper, and zinc transporters in rice.

Iron (Fe), manganese (Mn), copper (Cu), and zinc (Zn) are essential micronutrients that are necessary for plant growth and development, but can be toxic at supra-optimal levels. Plants have evolved a complex homeostasis network that includes uptake, transport, and storage of these metals. It was shown that the transcription factor (TF) complex OsbHLH156-OsIRO2 is activated under Fe deficient conditions and acts as a central regulator on Strategy II Fe acquisition. In this study, the role of the TF complex on Mn, Cu, and Zn uptake was evaluated. While Fe deficiency led to significant increases in shoot Mn, Cu, and Zn concentrations, the increases of these divalent metal concentrations were significantly suppressed in osbhlh156 and osiro2 mutants, suggesting that the TF complex plays roles on Mn, Cu, and Zn uptake and transport. An RNA-sequencing assay showed that the genes associated with Mn, Cu, and Zn uptake and transport were significantly suppressed in the osbhlh156 and osiro2 mutants. Transcriptional activation assays demonstrated that the TF complex could directly bind to the promoters of OsIRT1, OsYSL15, OsNRAMP6, OsHMA2, OsCOPT1/7, and OsZIP5/9/10, and activate their expression. In addition, the TF complex is required to activate the expression of nicotianamine (NA) and 2'-deoxymugineic acid (DMA) synthesis genes, which in turn facilitate the uptake and transport of Mn, Cu, and Zn. Furthermore, OsbHLH156 and OsIRO2 promote Cu accumulation to partially restore the Fe-deficiency symptoms. Taken together, OsbHLH156 and OsIRO2 TF function as core regulators not only in Fe homeostasis, but also in Mn, Cu, and Zn accumulation.

Selection of Arabidopsis transformants containing AtZAT12

This study aimed to select Arabidopsis seeds after transformation with the AtZAT12 gene via Agrobacterium tumerfaciens. ZAT12 is a transcription factor that inhibits other transcription factors FIT through the EAR motif. FIT itself is a central transcription factor that controls Fe uptake under Fe-deficient conditions. However, if Fe is absorbed excessively, it will produce reactive oxygen species that could damage cells. That is the reason why AtZAT12 transcription is elevated and FIT transcription is inhibited under Fe deficiency for 10 days. To investigate the function, the AtZAT12 gene was inserted into the pMDC107 vector for transformation into Arabidopsis. The T0 Arabidopsis seeds obtained after floral dip transformation were placed on 1% MS agar supplemented with 15 μg/mL Hygromycin B. Beforehand, the T0 seeds were sterilized and kept in the dark for stratification. Subsequently, the seed plates were subjected to a regime of 6 h of light, 48 h of dark and 24 h of light (3.25 d). The hygromycin B-resistant seedlings had long hypocotyls (~ 1.0 cm), while the non-resistant seedlings had short (~ 0.3 cm) hypocotyls. This method took only 3.25 days to identify transgenic Arabidopsis seedlings. After that, positive transgene lines were examined by PCR method for AtZAT12, and the expression of AtZAT12 was observed under microscope.

Calcium-dependent protein kinases CPK21 and CPK23 phosphorylate and activate the iron-regulated transporter IRT1 to regulate iron deficiency in Arabidopsis.

Iron (Fe) is an essential micronutrient for all organisms. Fe availability in the soil is usually much lower than that required for plant growth, and Fe deficiencies seriously restrict crop growth and yield. Calcium (Ca2+) is a second messenger in all eukaryotes; however, it remains largely unknown how Ca2+ regulates Fe deficiency. In this study, mutations in CPK21 and CPK23, which are two highly homologous calcium-dependent protein kinases, conferredimpaired growth and rootdevelopment under Fe-deficient conditions, whereas constitutively active CPK21 and CPK23 enhanced plant tolerance to Fe-deficient conditions. Furthermore, we found that CPK21 and CPK23 interacted with and phosphorylated the Fe transporter IRON-REGULATED TRANSPORTER1 (IRT1) at the Ser149 residue. Biochemical analyses and complementation of Fe transport in yeast and plants indicated that IRT1 Ser149 is critical for IRT1 transport activity. Taken together, these findings suggest that the CPK21/23-IRT1 signaling pathway is critical for Fe homeostasis in plants and provides targets for improving Fe-deficient environments and breeding crops resistant to Fe-deficient conditions.

Evidence That PbrSAUR72 Contributes to Iron Deficiency Tolerance in Pears by Facilitating Iron Absorption.

Iron is an essential trace element for plants; however, low bioactive Fe in soil continuously places plants in an Fe-deficient environment, triggering oxidative damage. To cope with this, plants make a series of alterations to increase Fe acquisition; however, this regulatory network needs further investigation. In this study, we found notably decreased indoleacetic acid (IAA) content in chlorotic pear (Pyrus bretschneideri Rehd.) leaves caused by Fe deficiency. Furthermore, IAA treatment slightly induced regreening by increasing chlorophyll synthesis and Fe2+ accumulation. At that point, we identified PbrSAUR72 as a key negative effector output of auxin signaling and established its close relationship to Fe deficiency. Furthermore, the transient PbrSAUR72 overexpression could form regreening spots with increased IAA and Fe2+ content in chlorotic pear leaves, whereas its transient silencing does the opposite in normal pear leaves. In addition, cytoplasm-localized PbrSAUR72 exhibits root expression preferences and displays high homology to AtSAUR40/72. This promotes salt tolerance in plants, indicating a putative role for PbrSAUR72 in abiotic stress responses. Indeed, transgenic plants of Solanum lycopersicum and Arabidopsis thaliana overexpressing PbrSAUR72 displayed less sensitivity to Fe deficiency, accompanied by substantially elevated expression of Fe-induced genes, such as FER/FIT, HA, and bHLH39/100. These result in higher ferric chelate reductase and root pH acidification activities, thereby hastening Fe absorption in transgenic plants under an Fe-deficient condition. Moreover, the ectopic overexpression of PbrSAUR72 inhibited reactive oxygen species production in response to Fe deficiency. These findings contribute to a new understanding of PbrSAURs and its involvement in Fe deficiency, providing new insights for the further study of the regulatory mechanisms underlying the Fe deficiency response.

Barley Cultivar Sarab 1 Has a Characteristic Region on the Thylakoid Membrane That Protects Photosystem I under Iron-Deficient Conditions.

The barley cultivar Sarab 1 (SRB1) can continue photosynthesis despite its low Fe acquisition potential via roots and dramatically reduced amounts of photosystem I (PSI) reaction-center proteins under Fe-deficient conditions. We compared the characteristics of photosynthetic electron transfer (ET), thylakoid ultrastructure, and Fe and protein distribution on thylakoid membranes among barley cultivars. The Fe-deficient SRB1 had a large proportion of functional PSI proteins by avoiding P700 over-reduction. An analysis of the thylakoid ultrastructure clarified that SRB1 had a larger proportion of non-appressed thylakoid membranes than those in another Fe-tolerant cultivar, Ehimehadaka-1 (EHM1). Separating thylakoids by differential centrifugation further revealed that the Fe-deficient SRB1 had increased amounts of low/light-density thylakoids with increased Fe and light-harvesting complex II (LHCII) than did EHM1. LHCII with uncommon localization probably prevents excessive ET from PSII leading to elevated NPQ and lower PSI photodamage in SRB1 than in EHM1, as supported by increased Y(NPQ) and Y(ND) in the Fe-deficient SRB1. Unlike this strategy, EHM1 may preferentially supply Fe cofactors to PSI, thereby exploiting more surplus reaction center proteins than SRB1 under Fe-deficient conditions. In summary, SRB1 and EHM1 support PSI through different mechanisms during Fe deficiency, suggesting that barley species have multiple strategies for acclimating photosynthetic apparatus to Fe deficiency.

Regulation of the iron-deficiency response by IMA/FEP peptide.

Iron (Fe) is an essential micronutrient for plant growth and development, participating in many significant biological processes including photosynthesis, respiration, and nitrogen fixation. Although abundant in the earth's crust, most Fe is oxidized and difficult for plants to absorb under aerobic and alkaline pH conditions. Plants, therefore, have evolved complex means to optimize their Fe-acquisition efficiency. In the past two decades, regulatory networks of transcription factors and ubiquitin ligases have proven to be essential for plant Fe uptake and translocation. Recent studies in Arabidopsis thaliana (Arabidopsis) suggest that in addition to the transcriptional network, IRON MAN/FE-UPTAKE-INDUCING PEPTIDE (IMA/FEP) peptide interacts with a ubiquitin ligase, BRUTUS (BTS)/BTS-LIKE (BTSL). Under Fe-deficient conditions, IMA/FEP peptides compete with IVc subgroup bHLH transcription factors (TFs) to interact with BTS/BTSL. The resulting complex inhibits the degradation of these TFs by BTS/BTSL, which is important for maintaining the Fe-deficiency response in roots. Furthermore, IMA/FEP peptides control systemic Fe signaling. By organ-to-organ communication in Arabidopsis, Fe deficiency in one part of a root drives the upregulation of a high-affinity Fe-uptake system in other root regions surrounded by sufficient levels of Fe. IMA/FEP peptides regulate this compensatory response through Fe-deficiency-triggered organ-to-organ communication. This mini-review summarizes recent advances in understanding how IMA/FEP peptides function in the intracellular signaling of the Fe-deficiency response and systemic Fe signaling to regulate Fe acquisition.

Site-Differentiated MnIIFeII Complex Reproducing the Selective Assembly of Biological Heterobimetallic Mn/Fe Cofactors.

Class Ic ribonucleotide reductases (RNRIc) and R2-like ligand-binding oxidases (R2lox) are known to contain heterobimetallic MnIIFeII cofactors. How these enzymes assemble MnIIFeII cofactors has been a long-standing puzzle due to the weaker binding affinity of MnII versus FeII. In addition, the heterobimetallic selectivity of RNRIc and R2lox has yet to be reproduced with coordination complexes, leading to the hypothesis that RNRIc and R2lox overcome the thermodynamic preference for coordination of FeII over MnII with their carefully constructed three-dimensional protein structures. Herein, we report the selective formation of a heterobimetallic MnIIFeII complex accomplished in the absence of a protein scaffold. Treatment of the ligand Py4DMcT (L) with equimolar amounts of FeII and MnII along with two equivalents of acetate (OAc) affords [LMnIIFeII (OAc)2(OTf)]+ (MnIIFeII) in 80% yield, while the diiron complex [LFeIIFeII(OAc)2(OTf)]+ (FeIIFeII) is produced in only 8% yield. The formation of MnIIFeII is favored regardless of the order of addition of FeII and MnII sources. X-ray diffraction (XRD) of single crystals of MnIIFeII reveals an unsymmetrically coordinated carboxylate ligand─a primary coordination sphere feature shared by both RNRIc and R2lox that differentiates the two metal binding sites. Anomalous XRD studies confirm that MnIIFeII exhibits the same site selectivity as R2lox and RNRIc, with the FeII (d6) center preferentially occupying the distorted octahedral site. We conclude that the successful assembly of MnIIFeII originates from (1) Fe-deficient conditions, (2) site differentiation, and (3) the inability of ligand L to house a dimanganese complex.

Identification of reference genes for RT-qPCR analysis across kiwifruit species under iron deficiency conditions

Selecting appropriate reference genes is crucial for the accuracy of gene expression analysis. Although rootstock species play vital roles in kiwifruit production, the reference genes has not been identified in kiwifruit roots and across kiwifruit species. Additionally, iron (Fe) deficiency has been frequently observed in kiwifruit orchards, but the reference genes is not validated. Here, we assessed ten candidate reference genes: actin (ACT), actin-depolymerizing factor family protein (ADF), ADP-ribosylation factor (ARF), eukaryotic translation initiation factor 5A (eIF5A), ribosomal protein L19 (RPL19), 40S ribosomal protein S17 (RPS17), suppressor of G2 allele of SKP1 (SGT1), translationally-controlled tumor protein (TCTP), translation initiation factor 2-γ (TIF2-γ) and ubiquitin-conjugating enzyme E2 variant (UBE2V), for their suitability as reliable internal controls in roots, stems and leaves of four kiwifruit species (Actinidia chinensis, A. macrosperma, A. polygama, and A. valvata) under direct and bicarbonate-induced Fe deficiency conditions. The expression stability of the candidate genes was evaluated by four statistical algorithms (geNorm, NormFinder, BestKeeper, and RefFinder). Based on the comprehensive ranking, we recommended TCTP + UBE2V as the best reference genes for roots, UBE2V + ACT for stems, RPL19 + ARF for leaves, and UBE2V + RPL19 for all the tissues. The reliability of the recommended reference genes was verified by six target genes involved in Fe uptake and transport. These results provide a basis for improving the accuracy of gene expression analysis and elucidating the molecular mechanisms of Fe deficiency adaptation in kiwifruit species.