Tolerance To Fe Deficiency Research Articles

An iron-deficiency tolerant genotype of sorghum effectively localizes iron to the thylakoid membranes of the bundle sheath cells

ABSTRACT Although sorghum (Sorghum bicolor L.), a C4 grass plant, requires a higher iron (Fe) concentration in its leaves for sufficient growth compared to C3 grass plants, there are differences in Fe-deficiency tolerance among sorghum genotypes. C4 plant sorghum localizes Fe in bundle sheath (BS) cells as a major site for CO2 assimilation; however, the response of chloroplasts in BS cells to Fe deficiency remains unknown. We compared the allocation of Fe and proteins involved in the photosystems between Fe-deficiency-tolerant and Fe-deficiency-susceptible sorghum genotypes. The distribution patterns of the Fe-requiring core proteins of photosystems I and II were the same in both genotypes, whereas the tolerant genotype, line D100, allocated more Fe to the BS thylakoid membranes than the susceptible genotype, regardless of Fe nutritional status and leaf Fe content. These results suggest that the tolerant D100 sorghum line has mechanisms to supply sufficient Fe to the BS thylakoid membranes.

Grain and shoot iron (Fe) content and root phytosiderophore release are the major determinants of Fe-deficiency tolerance index (FeDTI) and the reliable screening markers to breed Fe-efficient rice (Oryza sativa L.)

There is a need to exploit the genetic variability in rice to improve the Fe deficiency tolerance, particularly under aerobic conditions, and to improve the Fe uptake and accumulation in the grain to facilitate biofortification. The present research was conducted to ascertain the regulators and determinants of Fe-deficiency tolerance in rice. Fifty-seven diverse genotypes were investigated under Fe-deficient (1 µM, FDS, -Fe) and Fe-sufficient (100 µM, FSS, +Fe) nutrient solution cultures for growth and physiological attributes, Fe uptake and accumulation and root release of phytosiderophores (PS), etc., and Fe-deficiency tolerance index (FeDTI). A strong positive correlation was observed between root traits and the PS release. Further, a higher release of PS was evidenced as a major determinant of shoot Fe and grain Fe in rice particularly under Fe deficiency. Based on FeDTI, a total of ten rice genotypes were identified, and their Fe deficiency response was further validated on Fe deficient (∼2.1 ppm Fe, FeDS) and Fe-sufficient soils (∼10 ppm Fe, FeSS) in pot culture. Maintenance of high active Fe content and consequently a higher leaf chlorophyll content throughout the plant growth were extremely important determinants of grain yield and grain Fe fortification in rice under Fe deficiency than under the Fe sufficient condition. Based on the FeDTI, this study further identifies the Fe-deficiency tolerant rice genotypes which can be exploited through conventional and molecular breeding approaches to improve the Fe uptake efficiency and grain Fe content of the high-yielding rice genotypes.

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.

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.

Molecular cloning and functional characterization of MhHEC2-like genes in Malus halliana reveals it enhances Fe (iron) deficiency tolerance.

The basic helix-loop-helix (bHLH) family, as one of the largest families of transcription factors (TFs) in plants, plays crucial roles in regulating growth, development, and abiotic stress responses. However, studies on the association of the bHLH genes with apple iron (Fe) deficiency are limited. Here, multiple bHLH genes that responded to Fe deficiency were selected for quantitative real-time PCR in Malus halliana. The results showed that the expression of HEC2-like gene exerted more values compared to other genes under Fe deficiency stress, but the mechanism by which it regulates Fe deficiency stress is unclear. Subsequently, MhHEC2-like gene (ID: 103,455,961) was cloned from M. halliana for functional identification. We found that both transgenic Arabidopsis thaliana and tobacco displayed less chlorosis and more robust growth than wild-type (WT) controls under Fe deficiency stress. At the same time, the overexpressed apple calli grew prominently larger and better under Fe deficiency compared to the wild type. On the other hand, physiological index measurements revealed that overexpressed MhHEC2-like gene enhanced tolerance to Fe deficiency stress in A. thaliana and tobacco by promoting the synthesis of photosynthetic pigments, improving antioxidant enzyme activity, and enhancing Fe reduction, and strengthened tolerance to Fe deficiency stress in apple calli by reducing pH, boosting Fe reduction, and increasing antioxidant enzyme activity. To sum up, the overexpression of MhHEC2-like gene strengthened tolerance to Fe deficiency stress in Arabidopsis thaliana, tobacco, and apple calli.

Genome-Wide Association Analysis Reveals the Genetic Basis of Iron-Deficiency Stress Tolerance in Maize.

Iron (Fe) is an essential trace element for almost all organisms and is often the major limiting nutrient for normal growth. Fe deficiency is a worldwide agricultural problem, which affects crop productivity and product quality. Understanding the Fe-deficiency response in plants is necessary for improving both plant health and the human diet. In this study, Fe-efficient (Ye478) and Fe-inefficient maize inbred lines (Wu312) were used to identify the genotypic difference in response to low Fe stress during different developmental stages and to further determine the optimal Fe-deficient Fe(II) supply level which leads to the largest phenotypic difference between Ye478 and Wu312. Then, genome-wide association analysis was performed to further identify candidate genes associated with the molecular mechanisms under different Fe nutritional statuses. Three candidate genes involved in Fe homeostasis of strategy II plants (strategy II genes) were identified, including ZmDMAS1, ZmNAAT1, and ZmYSL11. Furthermore, candidate genes ZmNAAT1, ZmDMAS1, and ZmYSL11 were induced in Fe-deficient roots and shoots, and the expression of ZmNAAT1 and ZmDMAS1 responded to Fe deficiency more in shoots than in roots. Beyond that, several genes that may participate in Fe homeostasis of strategy I plants (strategy I genes) were identified, which were either encoding Fe transporters (ZmIRT1 and ZmZIP4), or acting as essential ethylene signal transducers (ZmEBF1). Interestingly, ZmIRT1, ZmZIP4, and ZmEBF1 were significantly upregulated under low Fe stress, suggesting that these genes may be involved in Fe-deficiency tolerance in maize which is considered as strategy II plant. This study demonstrates the use of natural variation in the association population to identify important genes associated with Fe-deficiency tolerance and may further provide insights for understanding the molecular mechanism underlying the tolerance to Fe-deficiency stress in maize.

Genome-Wide Identification and Transcript Analysis Reveal Potential Roles of Oligopeptide Transporter Genes in Iron Deficiency Induced Cadmium Accumulation in Peanut.

The oligopeptide transporter (OPT) family is a group of proton-coupled symporters that play diverse roles, including metal homeostasis. However, little is known about this family of peanuts. To reveal the potential roles of AhOPT genes in Fe/Cd interactions, peanut AhOPT genes were genome-widely identified, and the relationships between gene expression and Cd accumulation were detected in two contrasting peanut cultivars (Fenghua 1 and Silihong) under Fe-sufficient or Fe-deficient conditions. A total of 40 AhOPT genes were identified in peanuts, which were divided into two subfamilies (PT and YS). Most AhOPT genes underwent gene duplication events predominated by whole-genome duplication. Clustered members generally have similar protein structures. However, gene structural divergences occurred in most of the duplicated genes. Transcription analysis revealed that AhOPT3.2/3.4 and AhYSL3.1/3.2 might be responsible for Fe deficiency tolerance, while AhOPT3.1/3.4, AhOPT7.1/7.2, and AhYSL1.1 be involved in Fe/Cd interactions. These genes might be regulated by transcription factors, including ATHB-12, ATHB-6, DIVARICATA, MYB30, NAC02, DOF3.4, IDD7, and LUX. Reduced expressions of AhYSL3.1/3.2 and higher expressions of AhOPT3.4 might contribute to higher Fe-deficiency tolerance in Silihong. Higher expression of AhOPT7.3 and AhOPT6.1 might be responsible for low Cd accumulation in Fenghua 1. Our results confirmed that AhOPT3/6/7 and AhYSL1/3 might be involved in the transport of Fe and/or Cd in peanuts and provided new clues to understanding potential mechanisms of Fe/Cd interactions.

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.

Identification of Quantitative Trait Loci Associated With Iron Deficiency Tolerance in Maize.

Iron (Fe) is a limiting factor in crop growth and nutritional quality because of its low solubility. However, the current understanding of how major crops respond to Fe deficiency and the genetic basis remains limited. In the present study, Fe-efficient inbred line Ye478 and Fe-inefficient inbred line Wu312 and their recombinant inbred line (RIL) population were utilized to reveal the physiological and genetic responses of maize to low Fe stress. Compared with the Fe-sufficient conditions (+Fe: 200 μM), Fe-deficient supply (−Fe: 30 μM) significantly reduced shoot and root dry weights, leaf SPAD of Fe-efficient inbred line Ye478 by 31.4, 31.8, and 46.0%, respectively; decreased Fe-inefficient inbred line Wu312 by 72.0, 45.1, and 84.1%, respectively. Under Fe deficiency, compared with the supply of calcium nitrate (N1), supplying ammonium nitrate (N2) significantly increased the shoot and root dry weights of Wu312 by 37.5 and 51.6%, respectively; and enhanced Ye478 by 23.9 and 45.1%, respectively. Compared with N1, N2 resulted in a 70.0% decrease of the root Fe concentration for Wu312 in the −Fe treatment, N2 treatment reduced the root Fe concentration of Ye478 by 55.8% in the −Fe treatment. These findings indicated that, compared with only supplying nitrate nitrogen, combined supply of ammonium nitrogen and nitrate nitrogen not only contributed to better growth in maize but also significantly reduced Fe concentration in roots. In linkage analysis, ten quantitative trait loci (QTLs) associated with Fe deficiency tolerance were detected, explaining 6.2–12.0% of phenotypic variation. Candidate genes considered to be associated with the mechanisms underlying Fe deficiency tolerance were identified within a single locus or QTL co-localization, including ZmYS3, ZmPYE, ZmEIL3, ZmMYB153, ZmILR3 and ZmNAS4, which may form a sophisticated network to regulate the uptake, transport and redistribution of Fe. Furthermore, ZmYS3 was highly induced by Fe deficiency in the roots; ZmPYE and ZmEIL3, which may be involved in Fe homeostasis in strategy I plants, were significantly upregulated in the shoots and roots under low Fe stress; ZmMYB153 was Fe-deficiency inducible in the shoots. Our findings will provide a comprehensive insight into the physiological and genetic basis of Fe deficiency tolerance.

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.

Increase in root branching enhanced ferric-chelate reductase activity under iron stress in potato (Solanum tuberosum)

In response to Fe-deficiency, various dicots increase their root branching to improve ferric-chelate reductase activity. It still remains unclear, whether the response caused by Fe-deficiency ultimately improves the plant's ability to withstand Fe-deficiency. In this experiment conducted at ICAR-Central Potato Research Institute, Regional Station, Shillong during 2020, we demonstrated a substantial increase in the growth of the lateral root of potato genotype (CP 3443), when grown in the iron-stress, in relation to control plants, and the total lateral root number is well linked to ferric-chelate reductase (FCR) activity. These findings showed that FCR is involved in root Fe uptake in potato (Solanum tuberosum L.) and they suggest a role in Fe distribution throughout the plant. In view of these findings, the Fe-deficiency induced increases in the lateral roots suggested that these play a significant role in Fe-deficiency tolerance in potato, which can serve as useful trait for the identification of chlorosis tolerance and/or nutrient-deficiency stress.

The microbial siderophore desferrioxamine B inhibits Fe and Zn uptake in three spring wheat genotypes grown in Fe-deficient nutrient solution

While phytosiderophores (PS) are known to chelate Fe, the role that microbial siderophores play in iron and zinc transport in graminaceous plants has not been sufficiently investigated. The aim of this study was to assess the influence of the microbial siderophore DFOB (desferal, desferrioxamine B) in Fe and Zn transport and chlorosis resistance in three hard red spring wheat genotypes (Triticum aestivum L. cvs. 2375, Marquis, and Waldron). Plants were grown in Fe deficient nutrient solutions containing two DFOB levels (0 and 30 µM) for 6 weeks. Phytosiderophore concentrations were determined after 1, 2, 4 and 6 weeks of Fe deficiency. After 6 weeks plants were harvested and separated to root and shoot tissue to determine the dry matter and Fe and Zn content of the genotypes. There was no positive relationship between the amount of phytosiderophore exudation and differential tolerance of the wheat genotypes to Fe deficiency. Across most weeks, Fe-inefficient genotypes, Marquis and 2375, had no significant difference in the rate of phytosiderophore exudation compared to Fe-efficient genotype, Waldron, and only at 6 weeks in -DFOB treatment and 4 weeks in + DFOB treatment Waldron had a significantly higher rate of phytosiderophore exudation compared to Marquis and 2375. These findings suggested that mechanisms other than phytosiderophores might be involved in Fe deficiency tolerance of the wheat genotypes. There was not a strong correlation between phytosiderophore secretion and Fe and Zn transport to shoots of the studied wheat genotypes. Even though in most weeks Fe-inefficient genotype, Marquis, had the lowest phytosiderophore exudation among the studied genotypes, its ability to transport Fe and Zn to shoot was higher than Fe-efficient genotype, Waldron. These results also revealed that the relationship between Fe and Zn transport and tolerance to Fe deficiency was poor. Addition of DFOB decreased overall tolerance to Fe deficiency of the wheat genotype. In general, DFOB decreased Fe and Zn transport to the shoots of the Marquis and Waldron genotypes and only Zn transport to the shoots of the 2375 genotype. Further studies are needed to investigate the ability of these chelators in tolerance to Fe deficiency and Fe and Zn transport to shoot of wheat genotypes

Identification and function prediction of iron-deficiency-responsive microRNAs in citrus leaves.

The online version contains supplementary material available at 10.1007/s13205-021-02669-z.

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.

Physiological, transcriptomic, and metabolomic analyses reveal zinc oxide nanoparticles modulate plant growth in tomato

ZnO NPs increased metal nutrient accumulation and reprogrammed carbohydrate and amino acid metabolism in tomato plants. They also improved Fe deficiency tolerance by improving Fe accumulation, antioxidative capacity and contents of sugars and amino acids.

Ethylene Response Factors MbERF4 and MbERF72 Suppress Iron Uptake in Woody Apple Plants by Modulating Rhizosphere pH.

Iron (Fe) deficiency limits the yield of fruit trees. When subjected to Fe deficiency, H+ secretion increases in the rhizosphere of dicotyledonous plants and pH decreases. This leads to the acidification of the soil and promotes Fe3+ to Fe2+ conversion, which plants can better uptake. This study investigated the relationship between two inhibitory transcription factors (ethylene response factors MbERF4 and MbERF72) and the H+-ATPase gene MbHA2. Two species of apple woody plants were studied: the Fe-inefficient Malus baccata and the Fe-efficient Malus xiaojinensis. Yeast one-hybrid and electrophoretic mobility shift assays showed that both MbERF4 and MbERF72 bind to the GCC cassette (AGCCGCC) of the MbHA2 promoter. Moreover, yeast two-hybrid and bimolecular fluorescence complementation assays showed that MbERF4 interacts with MbERF72. Furthermore, β-glucuronidase and luciferase reporter assays showed that the MbERF4- and MbERF72-induced repression of MbHA2 expression is synergistic. Virus-induced gene silencing of MbERF4 or MbERF72 increased MbHA2 expression, and thus lowered the rhizosphere pH in M. baccata. Consequently, the high expressions of MbERF4 and MbERF72 induced by Fe deficiency contributed to the Fe sensitivity of M. baccata. Moreover, the low expressions of MxERF4 and MxERF72 contributed to the Fe-deficiency tolerance of M. xiaojinensis via different binding conditions to the HA2 promoter. In summary, this study identified the relationship of two inhibitory transcription factors with the H+-ATPase gene and proposed a model in which ERF4 and ERF72 affect the rhizosphere pH in response to Fe deficiency.

Comparative transcriptome analysis reveals key genes responsible for the homeostasis of iron and other divalent metals in peanut roots under iron deficiency

This study defines key genes involved in Fe homeostasis and reveals cultivar differences in Fe deficiency responses in peanuts. A comparative transcriptome analysis was conducted on two peanut cultivars, Silihong and Fenghua 1, under Fe-sufficient and -deficient conditions. Plant growth and metal contents were measured. Silihong is more tolerant to Fe-deficiency than Fenghua 1. Fe deficiency increased the uptake of Zn, Mn, Mg, Ca and Cu in peanut plants. A total of 56 and 19 transporter genes were identified to be differentially expressed genes in Silihong and Fenghua 1 respectively. Two cultivars shared twelve common differentially expressed genes encoding OPT3, FRO2, Nramp3, YSL3, IRT1, FER3 and FRO7. Silihong showed higher expressions of AHA4, COPT1, FRO2, IRT1, MTP4, MTP9, Nramp5, OPT3 and VITH4, while Fenghua 1 exhibited higher expressions of ATX1, HMA5, MPT1, OPT6, YSL3, YSL7, ZIP1, ZIP4, ZIP5 and ZIP11 under Fe deficiency. Peanuts overcome Fe deficiency by increasing Fe uptake and altering its transport pathway, in which FRO2, IRT1, Nramp3, YSL3 and OPT3 are involved. Higher expression of AHA4, FRO2, IRT1 and Nramp5 might be responsible for higher Fe-deficiency tolerance in Silihong. Induction of IRT1, Nramp5 and COPT1 by Fe deficiency contribute to increased metal uptake in peanut plants.

Enhancement of Iron Acquisition in Rice by the Mugineic Acid Synthase Gene With Ferric Iron Reductase Gene and OsIRO2 Confers Tolerance in Submerged and Nonsubmerged Calcareous Soils.

Iron (Fe) is an essential micronutrient for plants. Plants encounter Fe deficiency when grown in calcareous soil with low Fe availability, leading to reduced crop yield and agricultural problem. Rice acquires Fe from the soil via Strategy I–related system (ferrous ion uptake by OsIRT1) and Strategy II system (ferric ion uptake by chelation). However, rice plants have a weak ability in Fe(III) reduction and phytosiderophore secretion. We previously produced an Fe deficiency–tolerant rice harboring OsIRT1 promoter-refre1/372 (for higher Fe(III) reductase ability) and a 35S promoter-OsIRO2 (for higher phytosiderophore secretion). In this study, we produced a new Fe deficiency–tolerant rice by the additional introduction of a barley IDS3 genome fragment with refre1/372 and OsIRO2 (named as IRI lines) for further enhancement in Strategy II phytosiderophore productivity and better growth performance in various environments. Our results show that an enhanced tolerance was observed in OsIRO2 introduced line at the early growth stage, refre1/372 introduced line in the late stage, and RI line in all stages among five types of cultivation method. Moreover, we demonstrated that new IRI rice lines exhibited enhanced tolerance to Fe deficiency compared to nontransgenic (NT) rice and rice lines harboring the overexpressing OsIRO2 or the IDS3 fragment under submerged calcareous soil. The yields of IRI lines were ninefold higher than the NT line. Furthermore, under Fe-limited nonsubmerged calcareous soil condition (a new cultivation condition), IRI lines also conferred enhanced tolerance than NT, lines introducing only the OsIRT1 promoter-refre1/372 or overexpressing OsIRO2, and lines harboring both. Our results demonstrate that further enhancement of the Strategy II Fe uptake system by the mugineic acid synthase gene in addition to Fe uptake by enhanced ferric Fe reduction and phytosiderophore production in rice contributes Fe deficiency tolerance and broaden its utility in calcareous soil cultivation under paddy or nonpaddy field conditions.

Biodiversity within Medicago truncatula genotypes toward response to iron deficiency: Investigation of main tolerance mechanisms

AbstractIron (Fe) deficiency is one of the major environmental stresses affecting plant production in the world. The selection of tolerant genotypes is considered an effective remediation strategy for this stress. The present study was carried out in order to investigate the biodiversity within Medicago truncatula plants in response to Fe deficiency, to identify tolerant genotypes and to assess the main tolerance mechanisms. To do this, a screening test was performed on 20 M. truncatula genotypes cultivated in minimal medium. Biometric and physiological markers were analyzed, including plant biomass, chlorophyll and root architecture. Results showed a biodiversity among the 20 genotypes. Interestingly, Fe deficiency tolerance was highest in TN8.20 and A17 genotypes. However, the lowest tolerance behavior was observed in TN1.11 and TN6.18. In order to investigate the main tolerance mechanisms, an experiment was conducted in the hydroponic system on already selected genotypes. Assessment of Fe deficiency tolerance was performed mainly on plant growth parameters, Fe (III)‐chelate‐reductase activity, rhizosphere acidification and antioxidant system defense. The relative better tolerance of A17 and TN8.20 to Fe deficiency was positively correlated with their capacity to maintain higher Fe‐acquisition efficiency in roots via rhizosphere acidification and the stimulation of Fe (III)‐chelate‐reductase activity. Moreover, tolerant genotypes showed the lowest decreases in chlorophyll content and photosynthetic activity (CO2 assimilation) compared to the sensitive ones. The efficiency of antioxidant capacity of the tolerant genotypes was revealed in stimulation of catalase (CAT) and peroxidase (POX) activities as well as accumulation of polyphenols, leading to the maintenance of cell integrity under Fe deficiency.

Responses of aerobically grown iron chlorosis tolerant and susceptible rice (Oryza sativa L.) genotypes to soil iron management in an Inceptisol

ABSTRACT Iron deficiency is a serious nutritional disorder in aerobic rice, causing chlorosis, poor yields and reduced grain nutritional quality. The problem can be managed by complementing the use of Fe-efficient plant type with a suitable Fe management strategy. In the present paper, we report the effect of eight iron management practices to resolve the problem of iron (Fe) chlorosis through the use of an iron deficiency tolerant (IDTR) and iron deficiency susceptible (IDSR) rice genotype, i.e. Pusa 33 and ADT 39, respectively. Fe deficiency tolerance of these genotypes was related to the root release of PS which enabled a higher uptake of Fe in the IDTR than the IDSR under Fe deficiency. In general, IDTR performed better than the IDSR as evident from a significant increase in total iron, active iron, chlorophyll content and grain and straw yield. IDSR produced the highest grain and straw yield under slow iron release nano clay complex source. Grain Fe content of the IDTR and IDSR increased by 18.9 and 13.4%, respectively, under recommended dose of Fe. The results identified the most effective soil management strategies for the alleviating Fe deficiency chlorosis and improving Fe nutrition of both IDTR and IDSR genotypes.