Fe-deficiency Stress Response Research Articles

Transcription factors dealing with Iron-deficiency stress in plants: focus on the bHLH transcription factor family.

Iron (Fe), as an important micronutrient element necessary for plant growth and development, not only participates in multiple physiological and biochemical reactions in cells but also exerts a crucial role in respiration and photosynthetic electron transport. Since Fe is mainly present in the soil in the form of iron hydroxide, Fe deficiency exists universally in plants and has become an important factor triggering crop yield reduction and quality decline. It has been shown that transcription factors (TFs), as an important part of plant signaling pathways, not only coordinate the internal signals of different interaction partners during plant development, but also participate in plant responses to biological and abiotic stresses, such as Fe deficiency stress. Here, the role of bHLH transcription factors in the regulation of Fe homeostasis (mainly Fe uptake) is discussed with emphasis on the functions of MYB, WRKY and other TFs in the maintenance of Fe homeostasis. This review provides a theoretical basis for further studies on the regulation of TFs in Fe deficiency stress response.

The transcription factor MYC1 interacts with FIT to negatively regulate iron homeostasis in Arabidopsis thaliana.

Iron (Fe) is an indispensable trace mineral element for the normal growth of plants, and it is involved in different biological processes; Fe shortage in plants can induce chlorosis and yield loss. The objective of this research is to identify novel genes that participated in the regulation of Fe-deficiency stress in Arabidopsis thaliana. A basic helix-loop-helix (bHLH) transcription factor (MYC1) was identified to be interacting with the FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT) using a yeast-two-hybrid assay. Transcript-level analysis showed that there was a decrease in MYC1 expression in Arabidopsis to cope with Fe-deficiency stress. Functional deficiency of MYC1 in Arabidopsis leads to an increase in Fe-deficiency tolerance and Fe-accumulation, whereas MYC1-overexpressing plants have an enhanced sensitivity to Fe-deficiency stress. Additionally, MYC1 inhibited the formation of FIT and bHLH38/39 heterodimers, which suppressed the expressed level for Fe acquisition genes FRO2 and IRT1 during Fe-deficiency stress. These results showed that MYC1 functions as a negative modulator of the Fe-deficiency stress response by inhibiting the formation of FIT and bHLH38/39 heterodimers, thereby suppressing the binding of FIT and bHLH38/39 heterodimers to the promoters of FRO2 and IRT1 to modulate Fe intake during Fe-deficiency stress. Overall, the findings of this study elucidated the role of MYC1 in coping with Fe-deficiency stress, and provided potential targets for the developing of crop varieties resistant to Fe-deficiency stress.

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.

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.

Iron-Deficiency Responses in Cereal Seedlings

ABSTRACT Acidity release as a characteristic of iron (Fe) deficiency stress responses was investigated during early seedling establishment of maize (Zea mays L.), barley (Hordeum vulgare L.), winter wheat (Triticum aestivum L.), and winter rye (Secale cereale L.). Ferric reduction as another characteristic of Fe deficiency stress responses was also investigated in maize. This has previously been considered a process only occurring in iron-stressed dicotyledonous plants. Measurements were made of the Fe efflux from maize endosperm under Fe-deficient and non-limiting conditions. The scutellum of Fe-stressed cereal seedlings (all species investigated) increased agar acidification by 30–40%, while manganese (Mn) or zinc (Zn) stressed seedlings did not demonstrate this reaction. Among the maize genotypes studied (‘VIR-7569’ and ‘VIR-7882’), the Fe-stressed acid release was more prolonged in relatively less Fe-efficient cv. ‘VIR-7569.’ In maize, the induced enhancement of acid release was accompanied by an increase in Fe efflux from endosperm. Conversely, maize scutellum Fe3 +-reductase activity was not deficiency-dependent on Fe, indicating that enhanced acidity release is a biological phenomenon facilitating Fe supply at early development of graminaceous plants. In cereal seedlings, the coexistence of two marker responses to Fe-deficiency (Strategy I and Strategy II), which are usually typical of different taxonomic groups (dicotyledonous and graminaceous plants) can be regarded as evidence in favour of the hypothesis of common genesis in dicotyledonous and graminaceous plants.

Ethylene involvement in the regulation of the H +-ATPase CsHA1 gene and of the new isolated ferric reductase CsFRO1 and iron transporter CsIRT1 genes in cucumber plants

In previous works using ethylene inhibitors and precursors, it has been shown that ethylene participates in the regulation of several Fe deficiency stress responses by Strategy I plants, such as enhanced ferric reductase activity, rhizosphere acidification and subapical root hair development. Furthermore, recent evidence suggests that ethylene could regulate the expression of both the ferric reductase and the iron transporter genes of Strategy I plants by affecting the FER (or FER-like) transcription factor. Recently, two H +-ATPase genes have been isolated from cucumber roots, CsHA1 and CsHA2. CsHA1 is up-regulated under Fe deficiency while CsHA2 is constitutively expressed. In this work we have cloned and characterized the sequences of the ferric reductase ( CsFRO1) and the iron transporter ( CsIRT1) genes from cucumber ( Cucumis sativus L. cv Ashley). Expression of CsHA1, CsFRO1 and CsIRT1 is diminished in Fe-deficient roots by treatment with ethylene inhibitors, like Co (cobalt) or AOA (aminooxyacetic acid). Treatment with ethylene precursors, like ACC (1-aminocyclopropane-1-carboxylic acid) or Ethephon (2-chloroethylphosphonic acid), resulted in increased CsHA1, CsFRO1 and CsIRT1 transcript levels and increased ferric reductase activity during early stages of Fe deficiency. These results suggest that ethylene is involved in the regulation of CsHA1, CsFRO1 and CsIRT1 gene expression.

Physiological responses of tomato roots grown in organ culture to iron-deficiency stress

Roots of the Fe-efficient tomato (Lycopersicon esculentum Mill., cultivar Floradel) were cultured in an inorganic medium supplemented with glycine, thiamine, pyridoxine, and nicotinic acid, with sucrose as an energy and carbon source. Iron was supplied as ferric hydroxyethylethylenediaminetriacetic acid (FeHEDTA) and the initial PH was 5.5. Root growth was limited when less than 40 μm FeHEDTA was supplied. Roots grown at lower Fe concentrations decreased the pH of the FCR assay medium to a greater extent than did roots grown at higher Fe concentrations. Cultured roots grown with 10 μm FeHEDTA had increased levels of ferric chelate reductase (FCR) activity compared to roots grown with either lower or higher concentrations of FeHEDTA. Low FCR activity of roots grown at 2.5 or 5 μm FeHEDTA was attributed either to impaired metabolism due to Fe-deficiency or the lack of sufficient Fe for enhanced FCR formation. Roots of hydroponically grown tomato plants exhibited typical increases in FCR activity with Fe-deficiency. Based on these preliminary results, cultured roots were found to exhibit similar Physiological responses to Fe-deficiency stress as intact root systems. Cultured roots should provide a useful system for the investigation of the role of the root in plant Fe-deficiency stress responses as previously suggested by Bienfait et al.(Plant Physiol., 83, 244–247, 1987).

Ethylene involvement in the regulation of Fe-deficiency stress responses by Strategy I plants.

Plants have developed different mechanisms for the acquisition of iron (Fe). Depending on the mechanisms, plants are classified into two groups: Strategy I and Strategy II. Strategy I plants include all higher plants except the Gramineae, while Strategy II plants comprise the Gramineae. When plants suffer from Fe-deficiency, they develop several morphological and physiological changes in their roots, known as Fe-deficiency stress responses, which disappear when the plants acquire enough Fe. In Strategy I plants, these changes include subapical swelling with abundant root hairs, transfer cells, acidification of the rhizosphere, enhancement of the capacity to reduce Fe3+ to Fe2+, enhancement of the capacity for Fe2+ uptake, release of flavins, and others. The regulation of these responses is not fully understood but in recent years there has been evidence suggesting the involvement of ethylene in this process. This review summarises different results that support a role for this hormone in the regulation of Fe-deficiency stress responses by Strategy I plants.

Simultaneous Fe- and Cu-deficiency synergically accelerates the induction of several Fe-deficiency stress responses in Strategy I plants

Under Fe-deficiency, Strategy I plants develop certain Fe-deficiency stress responses in their roots, such as enhancement of ferric reducing capacity, acidification of the medium, release of flavins and development of subapical swollen root tips. Some of these Fe-deficiency stress responses are also induced by Cu-deficiency. The aim of this work was to test whether both deficiencies, when applied simultaneously, interact in the induction of enhanced ferric reducing capacity, and also of other Fe-deficiency stress responses. The experiments were carried out with soybean ( Glycine max L.), pea ( Pisum sativum L.), cucumber ( Cucumis sativus L.) and arabidopsis ( Arabidopsis thaliana L.) plants grown in nutrient solution lacking Fe, Cu or Fe and Cu simultaneously. After treatments, ferric reducing capacity and other Fe-deficiency stress responses were determined through time. At the end of the experiments, roots and young leaves from the different treatments were collected to determine their Fe content. Results suggest that both deficiencies (Fe and Cu) interact synergically in the induction of enhanced ferric reducing capacity and of other Fe-deficiency stress responses. The induction of these responses was faster when both deficiencies were applied simultaneously than when any of the deficiencies was applied alone. To explain these results, different hypotheses are suggested and discussed.

Iron deficiency enhances the levels of ascorbate, glutathione, and related enzymes in sugar beet roots.

The effects of Fe deficiency stress on the levels of ascorbate and glutathione, and on the activities of the enzymes ferric chelate reductase, glutathione reductase (EC 1.6.4.2), ascorbate free-radical reductase (EC 1.6.5.4) and ascorbate peroxidase (EC 1.11.1.11), have been investigated in sugar beet ( Beta vulgaris L.) roots. Plasma membrane vesicles and cytosolic fractions were isolated from the roots of the plants grown in nutrient solutions in the absence or presence of Fe for two weeks. Plants responded to Fe deficiency not only with a 20-fold increase in root ferric chelate reductase activity, but also with moderately increased levels of the general reductants ascorbate (2-fold) and glutathione (1.6-fold). The enzymes of the ascorbate-glutathione cycle in roots were also affected by Fe deficiency. Glutathione reductase activity was enhanced 1.4-fold with Fe deficiency, associated to an increased ratio of reduced to oxidized glutathione, from 3.1 to 5.2. The plasma membrane fraction from iron-deficient roots showed 1.7-fold higher ascorbate free-radical reductase activity, whereas in the cytosolic fraction the enzyme activity was not affected by Fe deficiency. The activity of the cytosolic hemoprotein ascorbate peroxidase decreased approximately by 50% with Fe deprivation. These results show that sugar beet responds to Fe deficiency with metabolic changes affecting components of the ascorbate-glutathione cycle in root cells. This suggests that the ascorbate-glutathione cycle would play certain roles in the general Fe deficiency stress responses in strategy I plants.

EFFECT OF IRON DEFICIENCY STRESS ON IRON-REDUCTASE ACTIVITY AT PLASMALEMMA OF APPLE ROOT CELLS

ABSTRACT Using two phase systems, plasma membrane (PM) of root cells was separated and purified from Malus xiaojinensis Cheng et Jiang, and iron (Fe)-reductase activities on PM analyzed, under conditions of both the normal Fe level (+Fe) and the Fe deficiency stress (−Fe) were compared. The results showed that FeCN-reductase on PM depended on NADH as the electron donor. The FeCN-reductase activity was 2.66 μmol L−1 mg−1 min−1 at +Fe, while the reductase activity was 4.92 μmol L−1 mg−1 min−1 at −Fe. Fe-EDTA-reductase could depend on either NADH or NADPH as the electron donor. There were no differences in Fe-EDTA-reductase activities on PM at either +Fe or −Fe, when the electron donor was NADPH. NADH being as the electron donor, however, the Fe-EDTA-reductase activity was 4.06 μmol L−1 mg−1 min−1 at −Fe, while the reductase activity was 2.73 μmol L−1 mg−1 min−1 at +Fe. Therefore, Fe3+ reduction on PM by Fe-reductase systems could be induced and also enhanced in M. xiaojinensis by Fe deficiency stress, which indicated that M. xiaojinensis had a stronger Fe deficiency stress response, and it was an Fe-efficient fruit genotype.

Iron resupply-mediated deactivation of Fe-deficiency stress responses in roots of sugar beet

Different root zones with or without increased Fe-reducing activities have been studied in Fe-deficient sugar beet (Beta vulgaris L.) plants after Fe resupply to the nutrient solution. The subapical regions of roots from Fe-deficient plants decreased by 19 and 88% their capacity to reduce ferric chelates after 24 and 96 h of Fe resupply, respectively. Iron resupply caused 52 and 96% decreases in phosphoenolpyruvate carboxylase activity in root extracts after 24 and 96 h, respectively, and also caused general decreases in other enzyme activities involved in carboxylic acid metabolism. The large pools of carboxylic acids in Fe-deficient roots decreased by 9 and 48% after 24 and 96 h of Fe resupply, respectively. The activities of pyruvate decarboxylase and lactate dehydrogenase, enzymes related to anaerobic metabolism, decreased by 88% after 24 h of Fe resupply. The mitochondrial quinone and pyridine nucleotide pools became more oxidised in the Fe-deficient root tips after Fe resupply. Iron resupply caused a 70% decrease in root oxygen consumption rates 96 h after Fe resupply. Results indicate that deactivation of the Fe deficiency stress responses of sugar beet roots upon Fe resupply occurs in a progressive manner in a time scale of several days.

Ethylene Production by Fe-deficient Roots and its Involvement in the Regulation of Fe-deficiency Stress Responses by Strategy I Plants

Species that showed marked morphological and physiological responses by their roots to Fe-deficiency (Strategy I plants) were compared with others that do not exhibit these responses (Strategy II plants). Roots from Fe-deficient cucumber (Cucumis sativusL. ‘Ashley’), tomato (Lycopersicon esculentumMill. T3238FER) and pea (Pisum sativumL. ‘Sparkle’) plants produced more ethylene than those of Fe-sufficient plants. The higher production of ethylene in Fe-deficient cucumber and pea plants occurred before Fe-deficient plants showed chlorosis symptoms and was parallel to the occurrence of Fe-deficiency stress responses. The addition of either the ethylene precursor ACC, 1-aminocyclopropane-1-carboxylic acid, or the ethylene releasing substance, Ethephon, to several Fe-sufficient Strategy I plants [cucumber, tomato, pea, sugar beet (Beta vulgarisL.),Arabidopsis (Arabidopsis thaliana(L.) Heynh ‘Columbia’), plantago (Plantago lanceolataL.)] promoted some of their Fe-deficiency stress responses: enhanced root ferric-reducing capacity and swollen root tips. By contrast, Fe-deficient roots from several Strategy II plants [maize (Zea maysL. ‘Funo’), wheat (Triticum aestivumL. ‘Yécora’), barley (Hordeum vulgareL. ‘Barbarrosa’)] did not produce more ethylene than the Fe-sufficient ones. Furthermore, ACC had no effect on the reducing capacity of these Strategy II plants and, except in barley, did not promote swelling of root tips. In conclusion, results suggest that ethylene is involved in the regulation of Fe-deficiency stress responses by Strategy I plants.

In-vitro-cultured subclover root can develop Fe-deficiency stress response

In-vitro-cultured subclover root can develop Fe-deficiency stress response

Fe-deficiency stress response in Fe-deficiency resistant and susceptible subterranean clover: importance of induced H+release

Plants can exhibit Fe-deficiency stress response when they are exposed to Fe-deficiency conditions. The relative importance of the individual Fe-deficiency stress-response reactions, for example, increased release of H+ from roots, enhanced root plasma membrane-bound Fe3+ -reductase activity, and release of reductant, in Fe-deficiency resistance is not understood. To address this problem, the Fe-deficiency stress response of two cultivars of subterranean clover (subclover), Koala (Trifolium brachycalycinum Katzn. and Morley) (Fe-deficiency resistant) and Karridale (T. subterraneum L.) (Fe-deficiency susceptible), were evaluated. The plants were cultured hydroponically at 0 (−Fe) and 30 (+Fe) μM Fe3+ EDTA conditions. After 6 d Fe treatment, the −Fe Koala and Karridale decreased the pH of the nutrient solution by 1.83 and 0.79 units, respectively, while the +Fe plants increased the pH of the nutrient solution. The H+ -release rate of the −Fe Koala determined 7 d after Fe treatment initiation was more than three times higher than that of the −Fe Karridale. The −Fe plants had a significantly enhanced Fe3+ -reduction rate compared with the +Fe plants for each cultivar, but the resistant cultivar did not exhibit a higher root Fe3+ -reduction rate than the susceptible cultivar at each Fe treatment. Reductant release from the roots of subclover was negligible. These results indicate that Fe-deficiency-induced H+ release may be the predominant factor influencing Fe-deficiency resistance in subclover.

Iron-Deficiency Stress Responses in Cucumber (Cucumis sativus L.) Roots (A Possible Role for Ethylene?).

Most dicotyledonous species respond to Fe deficiency by developing several mechanisms known as Fe-deficiency stress responses. To study the regulation of these responses, young cucumber plants (Cucumis sativus L. cv Ashley) were grown in nutrient solution for 11 d, being deprived of Fe during the last 4 or 5 d. Inhibitors of ethylene synthesis (2 or 10 [mu]M aminoethoxyvinylglycine; 10 or 20 [mu]M aminooxyacetic acid; 1, 2, 5, or 10 [mu]M Co2+ as CoCl2) or action (50, 200, or 800 [mu]M Ag+ as silver thiosulfate) were added to the nutrient solution at different times during this period of growth with no Fe. After this period, the reduction of Fe3+ ethylenedi-aminetetraacetate by the roots of entire plants was measured with ferrozine by reading the absorbance at 562 nm after 2 h. The presence of the ethylene inhibitors in the nutrient solution inhibited the Fe-deficiency stress responses ferric-reducing capacity and subapical root swelling. In another experiment, the addition of 1 [mu]M 1-aminocyclopropane-1-carboxylic acid (ACC), a precursor of ethylene synthesis, to the nutrient solution of plants having low ferric-reducing activity increased notably the ferric-reducing capacity and subapical root swelling. Here we show evidence that ethylene plays a role in the development of Fe-deficiency stress responses, since when ethylene synthesis or action was inhibited, the responses were also inhibited, and when a precursor of ethylene (ACC) was added, the responses were increased.

Iron Deficiency Stress Response of Epipremnum aureum and Philodendron scandens Subspecies Oxycardium

Summary Philodendron [ Philodendron scandens Koch, C. and H. Sello subspecies oxycardium (Schott) Bunt.] grown in Hoagland Solution Number 1, with all N supplied as nitrate, lowered solution pH from 5.1 to below 3 when the solution contained no Fe, 0.1 mM FeEDTA, or 6.3 mM Fe 2 O 3 . Philodendron with no Fe became severely chlorotic, while plants with Fe 2 O 3 or FeEDTA remained green. Reductant levels in the philodendron solutions did not differ regardless of Fe treatment. Pothos [ Epipremnum aureum (Linden and Andre) Bunt.] caused the solution pH to rise above 7 with FeEDTA, but the pH dropped with no Fe and at least initially with Fe 2 O 3 . With no Fe, pothos became severely chlorotic. With Fe 2 O 3 , pothos became slightly chlorotic but regreened as the pH dropped. After regreening of plants, the solution pH increased to above 7. Solutions of chlorotic pothos plants had reductant concentrations 10 to 25 times as high as those of Fe-sufficient plants. A macronutrient charge balance of leaf tissue indicated excess anion uptake only for the pothos receiving FeEDTA, which was consistent with the rise in nutrient solution pH. All other pothos and all philodendron treatments had excess cation uptake, which was consistent with the drop in nutrient solution pH in these treatments. Pothos had a strong Strategy I Fe-deficiency stress response, i.e. pH decrease and production of Fe reductant. Philodendron had some aspects of a Strategy I Fe-deficiency stress response but was unique because it lowered the pH of an all nitrate-N solution, regardless of Fe availability or plant Fe status.

An examination of Fe deficiency stress response in relation to Fe uptake in two sorghum hybrids and their parent cultivars

Abstract Two sorghum (Sorghum bicolor L. Moench) hybrids CSH‐10 and ‐ 11 and their parent cultivars 296‐A, SB‐1055 and MR‐715 were examined for their tolerance to Fe‐deficiency stress, and also Fe uptake. It was observed that there was greater reduction of pH of the nutrient media and more rapid recovery from chlorosis only in the female parent 296‐A, and to some degree in the hybrids, but not in the male parents. The results indicated that Fe uptake‐translocation were inversely related to their Fe stress tolerance.