Fe Deficiency Stress Research Articles

Mapping of the Quantitative Trait Loci and Candidate Genes Associated With Iron Efficiency in Maize.

Iron (Fe) is a mineral micronutrient for plants, and Fe deficiency is a major abiotic stress in crop production because of its low solubility under aerobic and alkaline conditions. In this study, 18 maize inbred lines were used to preliminarily illustrate the physiological mechanism underlying Fe deficiency tolerance. Then biparental linkage analysis was performed to identify the quantitative trait loci (QTLs) and candidate genes associated with Fe deficiency tolerance using the recombinant inbred line (RIL) population derived from the most Fe-efficient (Ye478) and Fe-inefficient (Wu312) inbred lines. A total of 24 QTLs was identified under different Fe nutritional status in the Ye478 × Wu312 RIL population, explaining 6.1–26.6% of phenotypic variation, and ten candidate genes were identified. Plants have evolved two distinct mechanisms to solubilize and transport Fe to acclimate to Fe deficiency, including reduction-based strategy (strategy I) and chelation-based strategy (strategy II), and maize uses strategy II. However, not only genes involved in Fe homeostasis verified in strategy II plants (strategy II genes), which included ZmYS1, ZmYS3, and ZmTOM2, but also several genes associated with Fe homeostasis in strategy I plants (strategy I genes) were identified, including ZmFIT, ZmPYE, ZmILR3, ZmBTS, and ZmEIN2. Furthermore, strategy II gene ZmYS1 and strategy I gene ZmBTS were significantly upregulated in the Fe-deficient roots and shoots of maize inbred lines, and responded to Fe deficiency more in shoots than in roots. Under Fe deficiency, greater upregulations of ZmYS1 and ZmBTS were observed in Fe-efficient parent Ye478, not in Fe-inefficient parent Wu312. Beyond that, ZmEIN2 and ZmILR3, were found to be Fe deficiency-inducible in the shoots. These findings indicate that these candidate genes may be associated with Fe deficiency tolerance in maize. This study demonstrates the use of natural variation to identify important Fe deficiency-regulated genes and provides further insights for understanding the response to Fe deficiency stress in maize.

Effects of Iron Deficiency Stress on Plant Growth and Quality in Flowering Chinese Cabbage and Its Adaptive Response

Iron (Fe) plays an important role in the growth and development of plants. The effects of different Fe concentrations, 1-aminocyclopropane-1-carboxylic acid (ACC), and cobalt chloride (Co2+) treatments on plant growth, quality and the adaptive response to Fe deficiency stress were investigated in flowering Chinese cabbage. The results revealed that Fe deficiency stress inhibited plant growth. The contents of vitamin C, soluble protein, and soluble sugar in leaves and stalks were significantly reduced under Fe deficiency stress, while the content of cellulose and nitrate was increased. Fe deficiency stress clearly reduced the net photosynthetic rate and nitrate reductase activity in the leaves. The balance system of active oxygen metabolism was destroyed due to Fe deficiency, resulting in the decrease in catalase activity, superoxide dismutase activity of roots and leaves, and peroxidase (POD) activity of leaves, while POD activity in roots and malonaldehyde content in roots and leaves were significantly increased. The treatments of Fe deficiency and ACC significantly reduced the pH value of the root medium, promoted the release of ethylene, and increased Fe3+ reductase activity, while Co2+ treatment showed results that were the opposite to those of Fe deficiency and ACC treatments. Thus, Fe deficiency stress affected nitrogen metabolism, photosynthesis, reactive oxygen metabolism, pH of root medium, and Fe3+ reductase activity, which was related to physiological adaptive response and tolerance mechanisms. We also found that ethylene could be involved in regulating the adaptive response to Fe deficiency stress in flowering Chinese cabbage.

MNB1 gene is involved in regulating the iron-deficiency stress response in Arabidopsis thaliana

BackgroundIron (Fe) is an essential mineral element that involves in many biological processes important for most plants growth and development. Fe-deficiency induces a complex series of responses in plants, involving physiological and developmental changes, to increase Fe uptake from soil. However, the molecular mechanism involved in plant Fe-deficiency is not well understood.ResultsHere, we found that the MNB1 (mannose-binding-lectin 1) gene is involved in the regulation of Fe-deficiency stress response in Arabidopsis thaliana. The expression abundance of MNB1 was inhibited by Fe-deficiency stress. Knockout of MNB1 led to enhanced Fe accumulation and tolerance, whereas the MNB1-overexpressing plants were sensitive to Fe-deficiency stress. Under conditions of normal and Fe-deficiency, lower H2O2 concentrations were detected in mnb1 mutant plants compared to wild type. On the contrary, higher H2O2 concentrations were found in MNB1-overexpressing plants, which was negatively correlated with malondialdehyde (MDA) levels. Furthermore, in mnb1 mutants, the transcription level of the Fe uptake- and translocation-related genes, FIT, IRT1, FRO2, ZIF, FRD3, NAS4, PYE and MYB72, were considerably elevated during Fe-deficiency stress, resulting in enhanced Fe uptake and translocation, thereby increasing Fe accumulation.ConclusionsTogether, our findings show that the MNB1 gene negatively controls the Fe-deficiency response in Arabidopsis via modulating reactive oxygen species (ROS) levels and the ROS-mediated signaling pathway, thereby affecting the expression of Fe uptake- and translocation-related genes.

Physiological and Molecular Changes in Cherry Red Tobacco in Response to Iron Deficiency Stress.

The genotype CR60 is a spontaneous Cherry Red variant (containing granular red dapples on flue-cured leaves) of the Yunyan 87 (Y87) tobacco; it accumulates higher concentration of iron (Fe) in leaves than Y87, but the physiological differences between them remain largely unknown. We investigated the physiological and molecular mechanisms of CR60 in response to Fe deficiency under hydroponic conditions. Our results showed no significant phenotypic difference between Y87 and CR60 at optimal (40 μM) and high Fe (160 and 320 μM) concentrations. By contrast, CR60 exhibited higher tolerance to Fe deficiency (0 μM) than Y87, as shown by higher concentrations of chlorophyll in CR60 leaves after 21-day Fe-deficiency stress. Transcriptome profiling coupled with RT-PCR analyses found that the expression of IRT1 and several genes associated with chlorophyll biosynthesis and photosynthesis (e.g., PRO, GSA, FD1, PsbO, and PC) was higher in CR60 than Y87. These results indicated that CR60 maintains sufficient Fe uptake, chlorophyll biosynthesis and photosynthetic rate when subjected to Fe starvation.

Identification of Malus halliana R2R3-MYB gene family under iron deficiency stress and functional characteristics of MhR2R3-MYB4 in Arabidopsis thaliana.

Iron (Fe) is an essential element for plant growth and development. Fe deficiency can trigger leaf chlorosis and reduce fruit yield. Therefore, it is necessary to explore transcription factors in response to Fe deficiency stress. A total of 29 MhR2R3-MYB transcription factors were identified based on the transcriptome of Malus halliana under Fe deficiency stress. A comprehensive analysis of physical and chemical properties, gene structures, conserved motif composition, evolutionary relationship and chromosome distribution was performed. Subsequently, based on the transcriptome, 14 genes with the most significant expression under Fe deficiency stress were screened for qRT-PCR verification. Among them,the functional characteristics of MhR2R3-MYB4 (MD05G1089600) were further studied in Arabidopsis thaliana. Expression of 13 out of these 14 genes was upregulated, only one was downregulated. Maximum upregulation of MhR2R3-MYB4 under Fe deficiency was 36.39-fold and 58.21-fold compared with day 0 in leaves and roots, respectively. Overexpression of MhR2R3-MYB4 enhanced tolerance to Fe deficiency in A. thaliana and led to multiple biochemical changes: transgenic lines have higher chl a, chl b and Fe2+ content, higher enzyme activity (SOD, POD, CAT and FCR) and lower chlorosis than the wild type in Fe deficiency conditions. We suggest that MhR2R3-MYB4 plays an important part in Fe deficiency stress, which may contribute to improve Fe deficiency tolerance of apple in future.

Nitric Oxide Prevents Fe Deficiency-Induced Photosynthetic Disturbance, and Oxidative Stress in Alfalfa by Regulating Fe Acquisition and Antioxidant Defense.

Iron (Fe) deficiency impairs photosynthetic efficiency, plant growth and biomass yield. This study aimed to reveal the role of nitric oxide (NO) in restoring Fe-homeostasis and oxidative status in Fe-deficient alfalfa. In alfalfa, a shortage of Fe negatively affected the efficiency of root andshoot length, leaf greenness, maximum quantum yield PSII (Fv/Fm), Fe, S, and Zn accumulation, as well as an increase in H2O2 accumulation. In contrast, in the presence of sodium nitroprusside (SNP), a NO donor, these negative effects of Fe deficiency were largely reversed. In response to the SNP, the expression of Fe transporters (IRT1, NRAMP1) and S transporter (SULTR1;2) genes increased in alfalfa. Additionally, the detection of NO generation using fluorescence microscope revealed that SNP treatment increased the level of NO signal, indicating that NO may act as regulatory signal in response to SNP in plants. Interestingly, the increase of antioxidant genes and their related enzymes (Fe-SOD, APX) in response to SNP treatment suggests that Fe-SOD and APX are key contributors to reducing ROS (H2O2) accumulation and oxidative stress in alfalfa. Furthermore, the elevation of Ascorbate-glutathione (AsA-GSH) pathway-related genes (GR and MDAR) Fe-deficiency with SNP implies that the presence of NO relates to enhanced antioxidant defense against Fe-deficiency stress.

Evaluation of the Potential Use of a Collagen-Based Protein Hydrolysate as a Plant Multi-Stress Protectant.

Protein hydrolysates (PHs) are a class of plant biostimulants used in the agricultural practice to improve crop performance. In this study, we have assessed the capacity of a commercial PH derived from bovine collagen to mitigate drought, hypoxic, and Fe deficiency stress in Zea mays. As for the drought and hypoxic stresses, hydroponically grown plants treated with the PH exhibited an increased growth and absorption area of the roots compared with those treated with inorganic nitrogen. In the case of Fe deficiency, plants supplied with the PH mixed with FeCl3 showed a faster recovery from deficiency compared to plants supplied with FeCl3 alone or with FeEDTA, resulting in higher SPAD values, a greater concentration of Fe in the leaves and modulation in the expression of genes related to Fe. Moreover, through the analysis of circular dichroism spectra, we assessed that the PH interacts with Fe in a dose-dependent manner. Various hypothesis about the mechanisms of action of the collagen-based PH as stress protectant particularly in Fe-deficiency, are discussed.

Melatonin enhances the tolerance to iron deficiency stress through scavenging ROS in apple

Iron (Fe) is an essential micronutrient for plants. Fe deficiency, resulting from poor availability induced by its insolubility in most soils, severely affects the growth and yield of apple (Malus domestica Borkh.). Except for the application of an Fe nutrition agent, there is a lack of efficient and environmently-friendly ways to relieve plants from Fe deficiency in a modern orchard. Here, we observed that melatonin (MT), as an efficient reactive oxygen species (ROS) scavenger, could alleviate the chlorosis of leaves in apple under Fe deficiency, following increased Fe content, decreased chlorophyll degradation and stable photosynthetic rate. Exogenous melatonin induced the synthesis of endogenous melatonin and improved the activities of antioxidant enzymes, which decreased the oxidative damage induced by Fe deficiency through properly scavenging O2•− and H2O2. In addition, exogenous melatonin promoted the expression of its synthetase genes, but decreased their protein level, inferring post-transcriptional regulation. In brief, melatonin improved the tolerance to Fe deficiency through ROS migration and chloroplast protection in apple. This work uncovered the role of melatonin on Fe deficiency tolerance and also provided a potential way to relieve plants from Fe deficiency stress for apple production.

Cloning and functional analysis of ZIP transporters in blueberry

Blueberry (Vaccinium spp., Vc) plants are highly susceptible to Fe deficiency stress. An understanding of the mechanisms involved in Fe as well as other mineral ions uptake and transportation is critical for the improvement of mineral ions use efficiency in the field practices. The functional roles of the VcZIPs in mineral ions uptake and transportation were not well understood. To elucidate the functions of ZIP transporter family that is involved in the uptake and transport of metal elements in blueberry, VcZIPs such as VcZIP1, VcZIP2, VcZIP6, VcZIP7, VcZIP8 and VcZIP11 were cloned and identified from blueberry genome. The results of functional complementarity and heterologous expression of yeast mutant verified that most of VcZIPs had the ability to transport Fe and Zn, and VcZIP1 and VcZIP7 could mediate the transport of Cd in yeast. Furthermore, higher chlorophyll contents and bigger crown diameter sizes were observed in VcZIP6, VcZIP7 and VcZIP8 over-expressed Arabidopsis thaliana at Fe deficient treatments. In this study, VcZIP1, VcZIP2, VcZIP6–VcZIP8 and VcZIP11 were Fe-deficient responsive genes in blueberry. VcZIP6–VcZIP8 participated in the uptake of Fe and likely contributed to Fe uptake and transportation in plants. VcZIP1, VcZIP7, VcZIP8 and VcZIP11 were involved transportation Zn in blueberry. Comparatively, higher Zn-transport abilities were observed in VcZIP1 and VcZIP7.

MxMPK6-2-bHLH104 interaction is involved in reactive oxygen species signaling in response to iron deficiency in apple rootstock.

Iron (Fe) is a trace element necessary for plant growth. Many land plants have evolved a set of mechanisms associated with the Fe absorption process to deal with the problem of insufficient Fe supply in the soil. During Fe absorption, reactive oxygen species (ROS) can be used as a signal to initiate a response to stress caused by Fe deficiency. However, the molecular mechanisms underlying the involvement of ROS in the Fe deficiency stress response remains unclear. In this study, we have identified a kinase, MxMPK6-2, from Malus xiaojinensis, an apple rootstock that is highly efficient at Fe absorption. MxMPK6-2 has been shown to be responsive to ROS signals during Fe deficiency, and MxMPK6-2 overexpression in apple calli enhanced its tolerance to Fe deficiency. We further screened for proteins in the Fe absorption pathway and identified MxbHLH104, a transcription factor which interacts with MxMPK6-2. MxbHLH104 can be phosphorylated by MxMPK6-2 in vivo, and we confirmed that its phosphorylation increased Fe absorption in apple calli under Fe deficiency, with the presence of ROS promoting this process. Overall, we have demonstrated that MxMPK6-2 is responsive to ROS signaling during Fe deficiency, and is able to control its response by regulating MxbHLH104.

Streptomyces hygroscopicus OsiSh-2-induced mitigation of Fe deficiency in rice plants

The limited availability of nutrient Fe severely impairs the health of almost all organisms. Endophytic actinobacteria can benefit the host plant in different ways. We previously inferred that the rice (Oryza) endophytic Streptomyces hygroscopicus OsiSh-2 possesses a highly efficient Fe-acquisition system. In this work, we first evaluated the effects of OsiSh-2 on the Fe-deficiency resilience of the host rice. The results demonstrated that the inoculation of OsiSh-2 considerably increased the plant biomass, Fe concentration and translocation factor, and chlorophyll content, and net leaf photosynthetic rate under Fe limiting condition. The expression of genes involved with Fe3+-reduction-related strategy in rice was up-regulated, while that involved with Fe3+-chelation-related strategy was down-regulated by OsiSh-2 treatment. Meanwhile, the OsiSh-2-rice symbiont showed enhancement of Fe3+-chelate reductase activity, total siderophore production, and acidification trend in the rhizosphere under Fe deficiency compared to plants without this endophyte. In conclusion, endophytic OsiSh-2 could protect plants against Fe-deficient stress by a sophisticated interaction with the host, including modulating Fe chelation, solubilization, reduction and translocation, ultimately leading to enhanced fitness of plant.

The bHLH protein OsIRO3 is critical for plant survival and iron (Fe) homeostasis in rice (Oryza sativa L.) under Fe-deficient conditions

ABSTRACT Iron (Fe) is an essential element for most organisms since it is involved in various biological reactions. Fe deficiency is a major constraint for plant growth and leads to low crop yields and poor nutritional quality. Fe uptake and translocation in plants require the coordinated expression of multiple genes, which is regulated by various transcription factors (TFs), especially members of the basic helix-loop-helix (bHLH) family. OsIRO3 was first reported as a repressor related to Fe homeostasis gene regulation in roots based on evidence in overexpressing rice. However, its functions in regulating rice growth and Fe homeostasis between roots and shoots during Fe deficiency is poorly understood. Here, we developed osiro3 knockout mutants by the CRISPR/Cas9 system. The leaves of osiro3 knockout mutants showed abnormal growth and development after Fe-deficiency treatment. Strong lesions occurred on the young leaves of osiro3 knockout mutants, which even led to plant death during severe Fe deficiency. Furthermore, accumulation of reactive oxygen species (ROS), Fe and manganese concentrations were all elevated in the shoots of osiro3 knockout mutants under the Fe deficiency stress. Quantitative RT-PCR showed that OsNAC4 for ROS induced plant hypersensitive cell death and OsFerritins for Fe storage and overload were all significantly activated in osiro3 knockout shoots after Fe deficiency treatment. In osiro3 knockout mutants, Fe-deficiency response genes were induced in roots, but suppressed in shoots, and furthermore Fe sufficiency/overload genes were induced in shoots under Fe-deficient conditions according to DNA microarray. Yeast two-hybrid analysis revealed a positive interaction between OsIRO3 and the homologous protein OsbHLH062, which was also transcriptionally increased in Fe-deficient roots. OsIRO3 is essential for maintaining plant survival in rice under Fe-deficient conditions and plays an important role in signal transmission from shoots to roots which is critical for plants to prevent Fe overload.

Effects of iron deficiency and exogenous sucrose on the intermediates of chlorophyll biosynthesis inMalushalliana.

Malus halliana is an iron (Fe)-efficient apple rootstock growing in calcareous soil that shows obvious 'greenness' traits during Fe deficiency. Recent studies have shown that exogenous sugars can be involved in abiotic stress. To identify the key regulatory steps of chlorophyll (Chl) biosynthesis in M. halliana under Fe deficiency and to verify whether exogenous sucrose (Suc) is involved in Fe deficiency stress, we determined the contents of the Chl precursor and the expression of several Chl biosynthetic genes in M. halliana. The results showed that Fe deficiency caused a significant increase in the contents of protoporphyrin IX (Proto IX), Mg-protoporphyrin IX (Mg-Proto IX) and protochlorophyllide (Pchlide) in M. halliana compared to the Fe-sensitive rootstock Malus hupehensis. Quantitative real-time PCR (RT-qPCR) also showed that the expression of protoporphyrinogen oxidase (PPOX), which synthesizes Proto IX, was upregulated in M. halliana and downregulated in M. hupehensis under Fe deficiency. Exogenous Suc application prominently enhanced the contents of porphobilinogen (PBG) and the subsequent precursor, whereas it decreased the level of δ-aminolaevulinic acid (ALA), suggesting that the transformation from ALA to PBG was catalyzed in M. halliana. Additionally, the transcript level of δ-aminolevulinate acid dehydratase (ALAD) was noticeably upregulated after exogenous Suc treatment. This result, combined with the precursor contents, indicated that Suc accelerated the steps of Chl biosynthesis by modulating the ALAD gene. Therefore, we conclude that PPOX is the key regulatory gene of M. halliana in response to Fe deficiency. Exogenous Suc enhances M. halliana tolerance to Fe deficiency stress by regulating Chl biosynthesis.

A long non-coding apple RNA, MSTRG.85814.11, acts as a transcriptional enhancer of SAUR32 and contributes to the Fe-deficiency response.

Iron (Fe) is an essential plant nutrient and its deficiency typically limits plant growth. Long non-coding (lnc) RNAs are involved in adaptive responses to nutrient stress; however, it is not known whether they function in the regulation of the canonical Fe-deficiency response. The expression of Malus domestica (apple) lncRNA MSTRG.85814 is induced by Fe deficiency, as identified by high-throughput strand-specific RNA-seq analysis of an apple homograft system. MSTRG.85814 has a complex structure, with 13 predicted RNA sequence variants, four of which are upregulated in the roots of plants experiencing Fe deficiency. We found that one MSTRG.85814 splice variant (MSTRG.85814.11) positively modulated its cis target mRNA derived from the small auxin upregulated gene SAUR32. This in turn promoted the expression of SAUR32 and caused an increase in the expression of a plasma membrane proton ATPase, AHA10. Using a pH imaging technique, a significant decrease in the apoplastic pH was observed to occur in the root tips of MSTRG.85814.11 or SAUR32-overexpressing apple plants. Thus MSTRG.85814.11 was shown to positively promote SAUR32 expression, which then activated proton extrusion involved in the Fe-deficiency response. These results reveal a mechanism by which lncRNA promotes environmental Fe-deficiency stress adaption.

Characterization of Fe deficiency induced RING finger family members in apple species

Iron (Fe) is a critical element for plants and Fe deficiency can cause adverse effects on their growth, development, yield and quality. RING finger family is a large group known for their role under abiotic stresses in plants. The main aim of this research work was to identify the RING finger family members that responded to Fe deficiency in apple species. Their genetic structure, molecular evolution, and expression levels were analyzed to study the underlying mechanism of RING finger genes under Fe deficiency stress. A total of 76 RING finger genes that responded to Fe deficiency were identified. Based on their structural characteristics and phylogenetic relationships, the identified genes were divided into four subfamilies: Group I, Group II, Group III and Group IV. Chromosomal localization demonstrated that the 76 RING finger genes were randomly distributed on 17 chromosomes. The genetic structure and amino-acid-motif encoded varied among different gene members. Fifteen pairs of RING finger genes were identified as segmental duplicated. Further, synteny analysis with Circos was performed to examine the evolutionary relationship between Malus domestica and other Rosaceae genomes. The results of qRT-PCR in Malus xiaojinensis showed expression levels of these genes under Fe deficiency, indicating that Fe deficiency could induce the expression of these genes, thus verifying the accuracy of transcriptome data. These results provided useful information about the evolutionary relationship of RING finger gene family, potentially important under Fe deficiency. Moreover, it will help to identify the function of these RING finger genes in future research.

Blueberry VcLon1 protease increases iron use efficiency by alleviating chloroplast oxidative stress

Aim to unveil the functions of VcLon1 in plant Fe use efficiency. RT-PCR was used to analyze the expression profile of VcLon1. VcLon1 was expressed in Nicotiana benthamiana, and its homologous tobacco gene was silenced using RNAi. The differences in biomass growth, oxidative stress and chloroplast ultrastructure between wild type and transgenic Nicotiana benthaminana were analyzed after being subjected to Fe deficiency stress. The RT-PCR showed that the expression of VcLon1 was significantly higher in young leaves than in old leaves or in leaves treated with Fe deficiency stress, indicating that VcLon1 is involved in reactive oxygen species (ROS) homeostasis induced by senescence or Fe deficiency. Compared with wild-type, overexpression of VcLon1 in Nicotiana benthamiana reduced damage to chloroplast structure induced by Fe deficiency. Furthermore, the contents of H2O2, MDA and carbonylated protein in leaves were kept at a low level, and antioxidant enzyme activities in chloroplasts such as SOD and APX are also generally higher in chloroplasts with VcLon1 overexpression. In contrast, the oxidative stress levels in NbLon1 RNAi silenced Nicotiana benthamiana leaves showed opposite trends. Under Fe deficiency stress, VcLon1 reduces oxidative damage in plants by degrading carbonylated proteins in organelles such as chloroplasts and effectively maintains the structure and function of organelles and the activity of functional proteins, contributing to Fe use efficiency in plants.

Silicon Alleviates Iron Deficiency in Barley by Enhancing Expression of Strategy II Genes and Metal Redistribution.

The beneficial effects of silicon (Si) have been shown on plants using reduction-based strategy for iron (Fe) acquisition. Here we investigated the influence of Si on Fe deficiency stress alleviation in barley (Hordeum vulgare), a crop plant which uses the chelation-based strategy for Fe acquisition. Analyses of chlorophyll content, ROS accumulation, antioxidative status, concentrations of Fe and other micronutrients, along with the expression of Strategy II genes were studied in response to Si supply. Si successfully ameliorated Fe deficiency in barley, diminishing chlorophyll and biomass loss, and improving the activity of antioxidative enzymes, resulting in lowered reactive oxidative species accumulation in the youngest leaves. Alleviation of Fe deficiency stress correlated well with the Si-induced increase of Fe content in the youngest leaves, while it was decreased in root. Moreover, Si nutrition lowered accumulation of other micronutrients in the youngest leaves of Fe deprived plants, by retaining them in the root. On the transcriptional level, Si led to an expedient increase in the expression of genes involved in Strategy II Fe acquisition in roots at the early stage of Fe deficiency stress, while decreasing their expression in a prolonged stress response. Expression of Strategy II genes was remarkably upregulated in the leaves of Si supplied plants. This study broadens the perspective of mechanisms of Si action, providing evidence for ameliorative effects of Si on Strategy II plants, including its influence on accumulation and distribution of microelements, as well as on the expression of the Strategy II genes.

Radiochemical evidence for the contribution of iron (using 59Fe) remobilization efficiency towards nitrogen (N) and Fe deficiency tolerance in wheat

Abstract Widespread deficiency of soil macro (N) and micro nutrient (Fe) limit crop productivity and nutritional quality of the produce worldwide. Iron is relatively immobile in plants however, its retranslocation can be facilitated by naturally produced chelator in the leaves. Synthesis of these metal-chelators depends on N nutrition of crops. The present study uses 59Fe tracer to measure the contribution of in-plant remobilization (from fully developed 2nd older leaf (OL) to a younger developing 3rd leaf (YL)) of relatively immobile iron towards N and Fe deficiency stress tolerance in Fe efficient bread and Fe inefficient durum wheat. Dual nutrient deficiency of nitrogen and iron induced senescence and hastened the process of chlorophyll degradation and induced a higher 59Fe remobilization from OL to YL. Further, 59Fe retranslocation was also highest under dual nutrient deficiency (N−Fe−). Percent 59Fe retranslocated into the YL of bread and durum wheat, respectively was higher in Fe deficient (N+Fe− and N−Fe−) than Fe sufficient (N+Fe+ and N+Fe−) treatments. Results clearly reveal that Fe deficiency tolerance response under N and Fe deficiency is chiefly determined an efficient Fe uptake and Fe retranslocation, respectively in the bread and the durum wheat.

Natural Variation in Physiological Responses of Tunisian Hedysarum carnosum Under Iron Deficiency.

Iron (Fe) is an essential element for plant growth and development. The cultivation of leguminous plants has generated strong interest because of their growth even on poor soils. Calcareous and saline soils with poor mineral availability are wide-spread in Tunisia. In an attempt to select better forage crops adapted to Tunisian soils, we characterized Fe deficiency responses of three different isolates of Hedysarum carnosum, an endemic Tunisian extremophile species growing in native stands in salt and calcareous soil conditions. H. carnosum is a non-model crop. The three isolates, named according to their habitats Karkar, Thelja, and Douiret, differed in the expression of Fe deficiency symptoms like morphology, leaf chlorosis with compromised leaf chlorophyll content and photosynthetic capacity and leaf metal contents. Across these parameters Thelja was found to be tolerant, while Karkar and Douiret were susceptible to Fe deficiency stress. The three physiological and molecular indicators of the iron deficiency response in roots, Fe reductase activity, growth medium acidification and induction of the IRON-REGULATED TRANSPORTER1 homolog, indicated that all lines responded to -Fe, however, varied in the strength of the different responses. We conclude that the individual lines have distinct adaptation capacities to react to iron deficiency, presumably involving mechanisms of whole-plant iron homeostasis and internal metal distribution. The Fe deficiency tolerance of Thelja might be linked with adaptation to its natural habitat on calcareous soil.

MdMYB58 Modulates Fe Homeostasis by Directly Binding to the MdMATE43 Promoter in Plants.

Nutrient element deprivation, such as iron (Fe) deficiency stress, is a major factor limiting plant survival and proliferation in marginal soils. To cope with a low Fe environment, plants have evolved elaborate mechanisms underlying Fe homeostasis via intricate transcriptional and post-transcriptional regulation. Here, we characterized the Fe deficiency-inducible MYB transcription factor MdMYB58 in apple plants. Overexpressing MdMYB58 resulted in the accumulation of Fe in the root of transgenic Arabidopsis and apple calli when they were exposed to low Fe available conditions. Further investigation revealed that MdMYB58 bound to the promoter of MdMATE43, and its homolog FRD3 in Arabidopsis. Transient expression and stable transgenic assays in apple calli indicated that MdMYB58 transcriptionally repressed MdMATE43 mRNA, as well as FRD3 in Arabidopsis. Interestingly, AtMYB58, the homolog of MdMYB58, possessed higher binding activities to MdMATE43 and FRD3, which suggests a potentially conserved feature of MYB58 binding to MATE transporters in plants. Additionally, MYB-MATE-mediated regulation of Fe homeostasis may be related to the PYE-related Fe deficiency regulatory network via MdSAT1, a member of the IVa subfamily of bHLH transcription factors. Co-overexpression of MdSAT1 competitively weakened MdMYB58-overexpression induced repression of MdMATE43 transcript abundancy by protein-protein interaction. Taken together, the newly identified MYB-bHLH transcription factor expands our understanding of multilevel molecular mechanisms that plants use to coordinate Fe demand with Fe uptake, transport, and tissue partitioning under low Fe conditions.