RESUMEN
Strigolactones (SLs) are a class of plant hormones that control plant architecture. SL levels in roots are determined by the nutrient conditions in the rhizosphere, especially the levels of nitrogen (N) and phosphorus (P). Our previous research showed that SL production is induced in response to deficiency of sulfur (S) as well as of N and P, and inhibits shoot branching, accelerates leaf senescence, and regulates lamina joint angle in rice. Here we show biomass, total S contents, and SL levels in rice under S-sufficient and S-deficient conditions using a split-root system. When one part of the root system was cultured in S-sufficient medium and the other in S-deficient medium (+S/-S), shoot fresh weight was unaffected relative to the +S/+S condition. The shoot weight significantly decreased in -S/-S condition. In contrast, there was no significant difference in root fresh weight between +S and -S conditions. In +S/-S condition, SL levels were systemically reduced in both parts, the shoot S content increased, but the root S content in S-deficient medium was unaffected relative to the -S/-S condition. These results suggest that shoots, not roots, recognize S deficiency, which induces SL production in roots.
Asunto(s)
Lactonas/metabolismo , Raíces de Plantas/metabolismo , Brotes de la Planta/metabolismo , Azufre/metabolismo , Biomasa , Plantones/metabolismoRESUMEN
MAIN CONCLUSION: Site-specific changes of photosynthesis, a relatively new concept, can be used to improve the productivity of critical food crops to mitigate the foreseen food crisis. Global food security is threatened by an increasing population and the effects of climate change. Large yield improvements were achieved in major cereal crops between the 1950s and 1980s through the Green Revolution. However, we are currently experiencing a significant decline in yield progress. Of the many approaches to improved cereal yields, exploitation of the mode of photosynthesis has been intensely studied. Even though the C4 pathway is considered the most efficient, mainly because of the carbon concentrating mechanisms around the enzyme ribulose-1,5-bisphosphate carboxylase/oxygenase, which minimize photorespiration, much is still unknown about the specific gene regulation of this mode of photosynthesis. Most of the critical cereal crops, including wheat and rice, are categorized as C3 plants based on the photosynthesis of major photosynthetic organs. However, recent findings raise the possibility of different modes of photosynthesis occurring at different sites in the same plant and/or in plants grown in different habitats. That is, it seems possible that efficient photosynthetic traits may be expressed in specific organs, even though the major photosynthetic pathway is C3. Knowledge of site-specific differences in photosynthesis, coupled with site-specific regulation of gene expression, may therefore hold a potential to enhance the yields of economically important C3 crops.
Asunto(s)
Carbono/metabolismo , Regulación de la Expresión Génica de las Plantas , Oryza/fisiología , Fotosíntesis/genética , Triticum/fisiología , Evolución Biológica , Cambio Climático , Productos Agrícolas , Grano Comestible , Ingeniería Genética , Variación Genética , Oryza/genética , Triticum/genéticaRESUMEN
Increased concentrations of atmospheric CO2 are predicted to reduce the content of essential elements such as protein, zinc, and iron in C3 grains and legumes, threatening the nutrition of billions of people in the next 50 years. However, this prediction has mostly been limited to grain crops, and moreover, we have little information about either the underlying mechanism or an effective intervention to mitigate these reductions. Here, we present a broader picture of the reductions in elemental content among crops grown under elevated CO2 concentration. By using a new approach, flow analysis of elements, we show that lower absorption and/or translocation to grains is a key factor underlying such elemental changes. On the basis of these findings, we propose two effective interventions-namely, growing C4 instead of C3 crops, and genetic improvements-to minimize the elemental changes in crops, and thereby avoid an impairment of human nutrition under conditions of elevated CO2.
Asunto(s)
Atmósfera/química , Dióxido de Carbono/fisiología , Producción de Cultivos/métodos , Productos Agrícolas/fisiología , Fotosíntesis/fisiología , Producción de Cultivos/tendencias , Productos Agrícolas/química , Fabaceae/química , Fabaceae/fisiología , Conducta Alimentaria/fisiología , Abastecimiento de Alimentos , Humanos , Micronutrientes/administración & dosificación , Micronutrientes/fisiología , Oryza/química , Oryza/fisiología , Plantas Modificadas Genéticamente/química , Plantas Modificadas Genéticamente/fisiologíaRESUMEN
Fish embryo toxicology is important because embryos are more susceptible than adults to toxicants. In addition, the aquatic toxicity of chemicals depends on water quality. We examined the toxicities to medaka embryos of three types of silver-AgNO3, silver nanocolloids (SNCs), and silver ions from silver nanoparticle plates (SNPPs)-under three pH conditions (4.0, 7.0, and 9.0) in embryo-rearing medium (ERM) or ultrapure water. Furthermore, we tested the later-life-stage effects of SNCs on medaka and their population growth. "Later-life-stage effects" were defined here as delayed toxic effects that occurred during the adult stage of organisms that had been exposed to toxicant during their early life stage only. AgNO3, SNCs, and silver ions were less toxic in ERM than in ultrapure water. Release of silver ions from the SNPPs was pH dependent: in ERM, silver toxicity was decreased owing to the formation of silver chloro-complexes. SNC toxicity was higher at pH 4.0 than at 7.0 or 9.0. AgNO3 was more toxic than SNCs. To observe later-life effects of SNCs, larvae hatched from embryos exposed to 0.01 mg/L SNCs in ultrapure water were incubated to maturity under clean conditions. The mature medaka were then allowed to reproduce for 21 days. Calculations using survival ratios and reproduction data indicated that the intrinsic population growth rate decreased after exposure of embryos to SNC. SNC exposure reduced the extinction time as a function of the medaka population-carrying capacity.
Asunto(s)
Embrión no Mamífero/efectos de los fármacos , Nanopartículas del Metal/toxicidad , Nitrato de Plata/toxicidad , Plata/toxicidad , Animales , Colorantes , Larva/efectos de los fármacos , Oryzias/embriología , Oryzias/crecimiento & desarrollo , Crecimiento Demográfico , Pruebas de Toxicidad , Contaminantes Químicos del Agua/toxicidadRESUMEN
Rice (Oryza sativa) secretes 2'-deoxymugineic acid (DMA) to acquire insoluble iron (Fe) from the rhizosphere. In rice, DMA is synthesized by DMA synthase 1 (OsDMAS1), a member of the aldo-keto reductase super family. We screened OsDMAS1 paralogs for DMA synthesis. None of these paralogs displayed in vitro DMA synthesis activity, suggesting that rice only harbors one functional DMAS. We further characterized OsDMAS1 mutant plants. We failed to screen homozygous knock-out plants (dmas-1), so we characterized DMAS knock-down plants (dmas-kd1 and dmas-kd2). Under Fe-deficient conditions, dmas-kd1 plants were more chlorotic compared to the wild-type (WT) plants, and the expression of OsNAS3, OsYSL2, OsIRT1, and OsIRO2 was significantly up-regulated in the dmas-kd1 mutant, indicating that metal homeostasis was significantly disturbed. The secretion of DMA in dmas-kd1 was not significantly reduced. The dmas-kd1 plants accumulated less Fe in their roots compared to WT plants when grown with 10 µM FeSO4. The dmas-kd1 plants accumulated more Zn in their roots compared to WT plants under Fe-deficient, Fe-EDTA, and FeSO4 conditions. In both dehusked rice seeds (brown rice) and polished rice, no differences were observed for Fe, Cu, or Mn accumulation, whereas dmas-kd1 seeds significantly accumulated more Zn in brown rice. Our data suggests that rice only harbors one functional gene for DMA synthesis. In addition, the knock-down of OsDMAS1 significantly up-regulates the genes involved in Fe uptake and homeostasis.
Asunto(s)
Ácido Azetidinocarboxílico/análogos & derivados , Regulación de la Expresión Génica de las Plantas , Hierro/metabolismo , Oryza/fisiología , Proteínas de Plantas/genética , Ácido Azetidinocarboxílico/metabolismo , Transporte Biológico , Homeostasis , Oryza/genética , Proteínas de Plantas/metabolismoRESUMEN
To investigate the effects of salinity on the behavior and toxicity of functionalized single-walled carbon nanotubes (SWCNTs), which are chemical modified nanotube to increase dispersibility, medaka embryos were exposed to non-functionalized single-walled carbon nanotubes (N-SWCNTs), water-dispersible, cationic, plastic-polymer-coated, single-walled carbon nanotubes (W-SWCNTs), or hydrophobic polyethylene glycol-functionalized, single-walled carbon nanotubes (PEG-SWCNTs) at different salinities, from freshwater to seawater. As reference nanomaterials, we tested dispersible chitin nanofiber (CNF), chitosan-chitin nanofiber (CCNF) and chitin nanocrystal (CNC, i.e. shortened CNF). Under freshwater conditions, with exposure to 10 mg l-1 W-SWCNTs, the yolk sacks of 57.8% of embryos shrank, and the remaining embryos had a reduced heart rate, eye diameter and hatching rate. Larvae had severe defects of the spinal cord, membranous fin and tail formation. These toxic effects increased with increasing salinity. Survival rates declined with increasing salinity and reached 0.0% in seawater. In scanning electron microscope images, W-SWCNTs, CNF, CCNF and CNC were adsorbed densely over the egg chorion surface; however, because of chitin's biologically harmless properties, only W-SWCNTs had toxic effects on the medaka eggs. No toxicity was observed from N-SWCNT and PEG-SWCNT exposure. We demonstrated that water dispersibility, surface chemistry, biomedical properties and salinity were important factors in assessing the aquatic toxicity of nanomaterials. Copyright © 2016 John Wiley & Sons, Ltd.
Asunto(s)
Embrión no Mamífero/patología , Nanotubos de Carbono/toxicidad , Oryzias/fisiología , Salinidad , Anomalías Inducidas por Medicamentos/patología , Animales , Quitina/química , Corion/química , Corion/patología , Desarrollo Embrionario/efectos de los fármacos , Agua Dulce/química , Larva , Nanotubos de Carbono/química , Agua de Mar/química , Saco Vitelino/patologíaRESUMEN
Iron is an essential metal element for all living organisms. Graminaceous plants produce and secrete mugineic acid family phytosiderophores from their roots to acquire iron in the soil. Phytosiderophores chelate and solubilize insoluble iron hydroxide in the soil. Subsequently, plants take up iron-phytosiderophore complexes through specific transporters on the root cell membrane. Phytosiderophores are also thought to be important for the internal transport of various transition metals, including iron. In this study, we analyzed TOM2 and TOM3, rice homologs of transporter of mugineic acid family phytosiderophores 1 (TOM1), a crucial efflux transporter directly involved in phytosiderophore secretion into the soil. Transgenic rice analysis using promoter-ß-glucuronidase revealed that TOM2 was expressed in tissues involved in metal translocation, whereas TOM3 was expressed only in restricted parts of the plant. Strong TOM2 expression was observed in developing tissues during seed maturation and germination, whereas TOM3 expression was weak during seed maturation. Transgenic rice in which TOM2 expression was repressed by RNA interference showed growth defects compared with non-transformants and TOM3-repressed rice. Xenopus laevis oocytes expressing TOM2 released (14)C-labeled deoxymugineic acid, the initial phytosiderophore compound in the biosynthetic pathway in rice. In onion epidermal and rice root cells, the TOM2-GFP fusion protein localized to the cell membrane, indicating that the TOM2 protein is a transporter for phytosiderophore efflux to the cell exterior. Our results indicate that TOM2 is involved in the internal transport of deoxymugineic acid, which is required for normal plant growth.
Asunto(s)
Proteínas Portadoras/metabolismo , Hierro/metabolismo , Proteínas de la Membrana/metabolismo , Oryza/metabolismo , Proteínas de Plantas/metabolismo , Animales , Ácido Azetidinocarboxílico/análogos & derivados , Ácido Azetidinocarboxílico/metabolismo , Transporte Biológico , Proteínas Portadoras/genética , Regulación de la Expresión Génica de las Plantas , Orden Génico , Genes de Plantas , Proteínas de la Membrana/genética , Oryza/genética , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente/genética , Plantas Modificadas Genéticamente/metabolismo , Regiones Promotoras Genéticas , Sideróforos/metabolismo , Distribución Tisular , Xenopus laevisRESUMEN
Strigolactones (SLs) act as plant hormones that inhibit shoot branching and stimulate secondary growth of the stem, primary root growth, and root hair elongation. In the moss Physcomitrella patens, SLs regulate branching of chloronemata and colony extension. In addition, SL-deficient and SL-insensitive mutants show delayed leaf senescence. To explore the effects of SLs on leaf senescence in rice (Oryza sativa L.), we treated leaf segments of rice dwarf mutants with a synthetic SL analogue, GR24, and evaluated their chlorophyll contents, ion leakage, and expression levels of senescence-associated genes. Exogenously applied GR24 restored normal leaf senescence in SL-deficient mutants, but not in SL-insensitive mutants. Most plants highly produce endogenous SLs in response to phosphate deficiency. Thus, we evaluated effects of GR24 under phosphate deficiency. Chlorophyll levels did not differ of in the wild-type between the sufficient and deficient phosphate conditions, but increased in the SL-deficient mutants under phosphate deficiency, leading in the strong promotion of leaf senescence by GR24 treatment. These results indicate that the mutants exhibited increased responsiveness to GR24 under phosphate deficiency. In addition, GR24 accelerated leaf senescence in the intact SL-deficient mutants under phosphate deficiency as well as dark-induced leaf senescence. The effects of GR24 were stronger in d10 compared to d17. Based on these results, we suggest that SLs regulate leaf senescence in response to phosphate deficiency.
Asunto(s)
Envejecimiento/efectos de los fármacos , Oryza/efectos de los fármacos , Oryza/metabolismo , Fosfatos/deficiencia , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Compuestos Heterocíclicos con 3 Anillos/farmacología , Lactonas/farmacología , Reguladores del Crecimiento de las Plantas/metabolismoRESUMEN
Graminaceous plants release mugineic acid family phytosiderophores to acquire iron from the soil. Recently, we reported that particular vesicles are involved in deoxymugineic acid (DMA) and nicotianamine (NA) biosynthesis and in DMA secretion from rice roots. A fusion protein of rice NA synthase 2 (OsNAS2) and synthetic green fluorescent protein (sGFP) was observed in a dot-like pattern, moving dynamically within the cell. OsNAS2 mutated in the tyrosine motif or di-leucine motif, which was reported to be involved in cellular transport, caused a disruption in vesicular movement and vesicular localization, respectively. Unlike OsNAS2, Arabidopsis NA synthases AtNAS1-4 were distributed uniformly in the cytoplasm with no localization in dot-like structures when transiently expressed in tobacco BY-2 cells. Interestingly, Fe deficiency-inducible genes were upregulated in the OsNAS2-sGFP plants, and the amounts of NA and DMA produced and DMA secreted by the OsNAS2-sGFP plants were significantly higher than in those by the non-transformants and domain-mutated lines. We propose a model for OsNAS2-localized vesicles in rice, and discuss why the introduction of OsNAS2-sGFP caused a disturbance in Fe homeostasis.
RESUMEN
Graminaceous plants release mugineic acid family phytosiderophores (MAs) to acquire iron from the soil. Here, we show that deoxymugineic acid (DMA) secretion from rice roots fluctuates throughout the day, and that vesicles accumulate in roots before MAs secretion. We developed transgenic rice plants that express rice nicotianamine (NA) synthase (NAS) 2 (OsNAS2) fused to synthetic green fluorescent protein (sGFP) under the control of its own promoter. In root cells, OsNAS2-sGFP fluorescence was observed in a dot-like pattern, moving dynamically within the cell. This suggests that these vesicles are involved in NA and DMA biosynthesis. A tyrosine motif and a di-leucine motif, which have been reported to be involved in cellular transport, are conserved in all identified NAS proteins in plants. OsNAS2 mutated in the tyrosine motif showed NAS activity and was localized to the vesicles; however, these vesicles stuck together and did not move. On the other hand, OsNAS2 mutated in the di-leucine motif lost NAS activity and did not localize to these vesicles. The amounts of NA and DMA produced and the amount of DMA secreted by OsNAS2-sGFP plants were significantly higher than in non-transformants and domain-mutated lines, suggesting that OsNAS2-sGFP, but not the mutated forms, was functional in vivo. Overall, the localization of NAS to vesicles and the transport of these vesicles are crucial steps in NA synthesis, leading to DMA synthesis and secretion in rice.
Asunto(s)
Transferasas Alquil y Aril/metabolismo , Hierro/metabolismo , Mutación , Oryza/enzimología , Raíces de Plantas/enzimología , Transferasas Alquil y Aril/química , Transferasas Alquil y Aril/genética , Microscopía Electrónica , Raíces de Plantas/metabolismo , Raíces de Plantas/ultraestructuraRESUMEN
Iron is essential for most living organisms. Plants transcriptionally induce genes involved in iron acquisition under conditions of low iron availability, but the nature of the deficiency signal and its sensors are unknown. Here we report the identification of new iron regulators in rice, designated Oryza sativa Haemerythrin motif-containing Really Interesting New Gene (RING)- and Zinc-finger protein 1 (OsHRZ1) and OsHRZ2. OsHRZ1, OsHRZ2 and their Arabidopsis homologue BRUTUS bind iron and zinc, and possess ubiquitination activity. OsHRZ1 and OsHRZ2 are susceptible to degradation in roots irrespective of iron conditions. OsHRZ-knockdown plants exhibit substantial tolerance to iron deficiency, and accumulate more iron in their shoots and grains irrespective of soil iron conditions. The expression of iron deficiency-inducible genes involved in iron utilization is enhanced in OsHRZ-knockdown plants, mostly under iron-sufficient conditions. These results suggest that OsHRZ1 and OsHRZ2 are iron-binding sensors that negatively regulate iron acquisition under conditions of iron sufficiency.
Asunto(s)
Hierro/metabolismo , Oryza/metabolismo , Proteínas de Plantas/metabolismo , Ubiquitina-Proteína Ligasas/metabolismo , Técnicas de Silenciamiento del Gen , Oryza/enzimología , Oryza/genética , Proteínas de Plantas/genética , Raíces de Plantas/enzimología , Raíces de Plantas/metabolismo , Ubiquitina-Proteína Ligasas/genética , Regulación hacia Arriba/genética , Zinc/metabolismoRESUMEN
In plants, iron (Fe) is essential for mitochondrial electron transport, heme, and Fe-Sulphur (Fe-S) cluster synthesis; however, plant mitochondrial Fe transporters have not been identified. Here we show, identify and characterize the rice mitochondrial Fe transporter (MIT). Based on a transfer DNA library screen, we identified a rice line showing symptoms of Fe deficiency while accumulating high shoot levels of Fe. Homozygous knockout of MIT in this line resulted in a lethal phenotype. MIT localized to the mitochondria and complemented the growth of Δmrs3Δmrs4 yeast defective in mitochondrial Fe transport. The growth of MIT-knockdown (mit-2) plants was also significantly impaired despite abundant Fe accumulation. Further, the decrease in the activity of the mitochondrial and cytosolic Fe-S enzyme, aconitase, indicated that Fe-S cluster synthesis is affected in mit-2 plants. These results indicate that MIT is a mitochondrial Fe transporter essential for rice growth and development.
Asunto(s)
Proteínas de Transporte de Catión/metabolismo , Hierro/metabolismo , Proteínas Mitocondriales/metabolismo , Oryza/crecimiento & desarrollo , Oryza/metabolismo , Proteínas de Plantas/metabolismo , Transporte Biológico , Proteínas de Transporte de Catión/genética , Mitocondrias/genética , Mitocondrias/metabolismo , Proteínas Mitocondriales/genética , Oryza/genética , Proteínas de Plantas/genética , Transporte de ProteínasRESUMEN
It has been thought that phosphorus in biominerals made of amorphous calcium carbonate (ACC) might be related to ACC formation, but no such phosphorus-containing compounds have ever been identified. Crustaceans use ACC biominerals in exoskeleton and gastroliths so that they will have easy access to calcium carbonate inside the body before and after molting. We have identified phosphoenolpyruvate and 3-phosphoglycerate, intermediates of the glycolytic pathway, in exoskeleton and gastroliths and found them important for stabilizing ACC.
Asunto(s)
Carbonato de Calcio/metabolismo , Crustáceos/metabolismo , Animales , Calcificación Fisiológica , Carbonato de Calcio/química , Ácidos Glicéricos/química , Ácidos Glicéricos/metabolismo , Glucólisis , Espectroscopía de Resonancia Magnética , Microscopía Electrónica de Rastreo , Fosfoenolpiruvato/química , Fosfoenolpiruvato/metabolismoRESUMEN
Morphology and crystallographic orientations of coccoliths, Pleurochrysis carterae, at the various growth stages were investigated using electron back-scattered diffraction analyses and scanning electron microscope (SEM) stereo-photogrammetry to understand the developments of two different coccolith units, namely V and R units. SEM observation indicates that the immature coccolith units at the earliest stage were not perfectly fixed on the organic base plates and several units were often lacked. The all units showed platy morphology and often lay parallel to the organic base plate. Their crystal orientations were close to that of the mature R units. With further growth, the platy morphology changes to a trapezoid to anvil-shape for both units, resulting in the interlocking structure of VR units. Morphological analyses present that the edges of the platy crystals parallel to the organic base plate were estimated as <48 1>, and their inner/upper surfaces were estimated as {10 14}. As they interlocked further, R units inclined more outward to develop the inner tube elements with {10 1 4} and then each unit develops differently distal and proximal shield elements, which are respectively estimated as {10 14} in the distal view and {2 1 10} planes in the proximal view. Based on the above results, the formation of different coccolith units and their growth were discussed.
Asunto(s)
Haptophyta/crecimiento & desarrollo , Haptophyta/ultraestructura , Microscopía Electrónica de Rastreo , Microscopía Electrónica de Transmisión , FotogrametríaRESUMEN
Eukaryotic organisms have developed diverse mechanisms for the acquisition of iron, which is required for their survival. Graminaceous plants use a chelation strategy. They secrete phytosiderophore compounds, which solubilize iron in the soil, and then take up the resulting iron-phytosiderophore complexes. Bacteria and mammals also secrete siderophores to acquire iron. Although phytosiderophore secretion is crucial for plant growth, its molecular mechanism remains unknown. Here, we show that the efflux of deoxymugineic acid, the primary phytosiderophore from rice and barley, involves the TOM1 and HvTOM1 genes, respectively. Xenopus laevis oocytes expressing TOM1 or HvTOM1 released (14)C-labeled deoxymugineic acid but not (14)C-labeled nicotianamine, a structural analog and biosynthetic precursor of deoxymugineic acid, indicating that the TOM1 and HvTOM1 proteins are the phytosiderophore efflux transporters. Under conditions of iron deficiency, rice and barley roots express high levels of TOM1 and HvTOM1, respectively, and the overexpression of these genes increased tolerance to iron deficiency. In rice roots, the efficiency of deoxymugineic acid secretion was enhanced by overexpression of TOM1 and decreased by its repression, providing further evidence that TOM1 encodes the efflux transporter of deoxymugineic acid. We have also identified two genes encoding efflux transporters of nicotianamine, ENA1 and ENA2. Our identification of phytosiderophore efflux transporters has revealed the final piece in the molecular machinery of iron acquisition in graminaceous plants.
Asunto(s)
Hordeum/metabolismo , Hierro/metabolismo , Proteínas de Transporte de Membrana/metabolismo , Oryza/metabolismo , Proteínas de Plantas/metabolismo , Sideróforos/metabolismo , Secuencia de Aminoácidos , Animales , Ácido Azetidinocarboxílico/metabolismo , Transporte Biológico/fisiología , Expresión Génica , Hordeum/genética , Proteínas de Transporte de Membrana/genética , Datos de Secuencia Molecular , Oocitos , Oryza/genética , Proteínas de Plantas/genética , Sideróforos/genética , Xenopus laevisRESUMEN
Iron uptake and translocation in plants are important processes for both plant and human nutrition, whereas relatively little is known about the molecular mechanisms of iron transport within the plant body. Several reports have shown that yellow stripe 1 (YS1) and YS1-like (YSL) transporters mediate metal-phytosiderophore uptake and/or metal-nicotianamine translocation. Among the 18 YSL genes in rice (OsYSLs), OsYSL18 is predicted to encode a polypeptide of 679 amino acids containing 13 putative transmembrane domains. An OsYSL18-green fluorescent protein (GFP) fusion was localized to the plasma membrane when transiently expressed in onion epidermal cells. Electrophysiological measurements using Xenopus laevis oocytes showed that OsYSL18 transports iron(III)-deoxymugineic acid, but not iron(II)-nicotianamine, zinc(II)-deoxymugineic acid, or zinc(II)-nicotianamine. Reverse transcriptase PCR analysis revealed more OsYSL18 transcripts in flowers than in shoots or roots. OsYSL18 promoter-beta-glucuronidase (GUS) analysis revealed that OsYSL18 was expressed in reproductive organs including the pollen tube. In vegetative organs, OsYSL18 was specifically expressed in lamina joints, the inner cortex of crown roots, and phloem parenchyma and companion cells at the basal part of every leaf sheath. These results suggest that OsYSL18 is an iron-phytosiderophore transporter involved in the translocation of iron in reproductive organs and phloem in joints.
Asunto(s)
Ácido Azetidinocarboxílico/análogos & derivados , Compuestos Férricos/metabolismo , Proteínas de Transporte de Membrana/metabolismo , Oryza/metabolismo , Proteínas de Plantas/metabolismo , Secuencia de Aminoácidos , Animales , Ácido Azetidinocarboxílico/metabolismo , Secuencia de Bases , Transporte Biológico Activo , Cartilla de ADN/genética , Femenino , Expresión Génica , Genes de Plantas , Técnicas In Vitro , Proteínas de Transporte de Membrana/genética , Datos de Secuencia Molecular , Oocitos/metabolismo , Oryza/anatomía & histología , Oryza/genética , Floema/metabolismo , Filogenia , Proteínas de Plantas/genética , Plantas Modificadas Genéticamente , Proteínas Recombinantes de Fusión/genética , Proteínas Recombinantes de Fusión/metabolismo , Homología de Secuencia de Aminoácido , Sideróforos/genética , Sideróforos/metabolismo , Distribución Tisular , Xenopus laevisRESUMEN
Typical for a graminaceous plant, barley secretes mugineic acid-family phytosiderophores (MAs) to acquire iron (Fe). Under Fe-deficient conditions, MAs secretion from barley roots increases markedly. Secretion shows a diurnal pattern, with a clear peak 2-3 h after sunrise and cessation within a few hours. Microarray analyses were performed to profile the Fe deficiency-inducible genes in barley roots and diurnal changes in the expression of these genes. Genes encoding enzymes involved in MAs biosynthesis, the methionine cycle, and methionine biosynthesis were highly induced by Fe deficiency. The expression of sulfate transporters was also upregulated by Fe deficiency. Therefore, all of the genes participating in the MAs pathway from sulfur uptake and assimilation to the biosynthesis of MAs were upregulated in Fe-deficient barley roots. In contrast to MAs secretion, the transcript levels of these genes did not show diurnal changes. The amount of endogenous MAs gradually increased during the day after MAs secretion ceased, and was highest before secretion began. These results show that MAs biosynthesis, including the supply of the substrate methionine, occurs throughout the day, and biosynthesized MAs likely accumulate in barley roots until their secretion into the rhizosphere. In contrast, the levels of transcripts encoding an Fe(III)-MAs complex transporter, two putative metal-MAs complex transporters, and HvYS1 were also increased in Fe-deficient barley roots, and the levels of two of these transcripts showed diurnal rhythms. The Fe(III)-MAs complex transporters may absorb Fe(III)-MAs diurnally, synchronous with the diurnal secretion of MAs.
Asunto(s)
Regulación de la Expresión Génica de las Plantas , Hordeum/genética , Deficiencias de Hierro , Raíces de Plantas/genética , Ácido Azetidinocarboxílico/análogos & derivados , Ácido Azetidinocarboxílico/química , Northern Blotting , Ritmo Circadiano/genética , Ritmo Circadiano/efectos de la radiación , Regulación de la Expresión Génica de las Plantas/efectos de la radiación , Genes de Plantas , Hordeum/efectos de la radiación , Luz , Metionina/metabolismo , Raíces de Plantas/efectos de la radiación , Regiones Promotoras Genéticas/genética , ARN Mensajero/genética , ARN Mensajero/metabolismo , Sideróforos/metabolismo , Factores de Tiempo , Regulación hacia Arriba/genética , Regulación hacia Arriba/efectos de la radiaciónRESUMEN
Transmission electron microscopy revealed the presence of electron-dense bodies (EDB) in the cytosol of the acidophilic, thermophilic red alga Cyanidium caldarium. These bodies contain almost exclusively Fe, P, and O and can play a role in Fe storage. (31)P-nuclear magnetic resonance analysis identified a sharp signal at -23.3 ppm, which was attributed to the phosphate groups of the inner portions of polyphosphate chains. From this evidence, as well as that of a previous ESR study (Nagasaka et al., BioMetals 16:465-470, 2003), it can be concluded that polyphosphates are the major anionic constituents of the EDB. Omission of Fe from the culture medium resulted in substantially decreased polyphosphate levels, demonstrating the control of cellular polyphosphate content by the Fe status of the culture medium.
Asunto(s)
Hierro/farmacología , Polifosfatos/análisis , Rhodophyta/efectos de los fármacos , Medios de Cultivo/metabolismo , Medios de Cultivo/farmacología , Hierro/metabolismo , Espectroscopía de Resonancia Magnética , Microscopía Electrónica de Transmisión , Polifosfatos/metabolismo , Rhodophyta/crecimiento & desarrollo , Rhodophyta/metabolismoRESUMEN
Glutathione reductase (GR) plays an important role in the response to biotic and abiotic stresses in plants. We studied the expression patterns and enzyme activities of GR in graminaceous plants under Fe-sufficient and Fe-deficient conditions by isolating cDNA clones for chloroplastic GR (HvGR1) and cytosolic GR (HvGR2) from barley. We found that the sequences of GR1 and GR2 were highly conserved in graminaceous plants. Based on their nucleotide sequences, HvGR1 and HvGR2 were predicted to encode polypeptides of 550 and 497 amino acids, respectively. Both proteins showed in vitro GR activity, and the specific activity for HvGR1 was 3-fold that of HvGR2. Northern blot analyses were performed to examine the expression patterns of GR1 and GR2 in rice (Os), wheat (Ta), barley (Hv), and maize (Zm). HvGR1, HvGR2, and TaGR2 were upregulated in response to Fe-deficiency. Moreover, HvGR1 and TaGR1 were mainly expressed in shoot tissues, whereas HvGR2 and TaGR2 were primarily observed in root tissues. The GR activity increased in roots of barley, wheat, and maize and shoot tissues of rice, barley, and maize in response to Fe-deficiency. Furthermore, it appeared that GR was not post-transcriptionally regulated, at least in rice, wheat, and barley. These results suggest that GR may play a role in the Fe-deficiency response in graminaceous plants.
Asunto(s)
Glutatión Reductasa/genética , Hordeum/enzimología , Regulación hacia Arriba/genética , Secuencia de Aminoácidos , Northern Blotting , Western Blotting , Cloroplastos/enzimología , Clonación Molecular , Citosol/enzimología , ADN Complementario/química , ADN Complementario/genética , Regulación Enzimológica de la Expresión Génica/efectos de los fármacos , Regulación de la Expresión Génica de las Plantas/efectos de los fármacos , Glutatión/metabolismo , Glutatión Reductasa/metabolismo , Hierro/metabolismo , Hierro/farmacología , Isoenzimas/genética , Isoenzimas/metabolismo , Modelos Biológicos , Datos de Secuencia Molecular , Oryza/genética , Filogenia , Análisis de Secuencia de ADN , Homología de Secuencia de Aminoácido , Triticum/genética , Regulación hacia Arriba/efectos de los fármacos , Zea mays/genéticaRESUMEN
Graminaceous plants have evolved a unique mechanism to acquire iron through the secretion of a family of small molecules, called mugineic acid family phytosiderophores (MAs). All MAs are synthesized from l-Met, sharing the same pathway from l-Met to 2'-deoxymugineic acid (DMA). DMA is synthesized through the reduction of a 3''-keto intermediate by deoxymugineic acid synthase (DMAS). We have isolated DMAS genes from rice (OsDMAS1), barley (HvDMAS1), wheat (TaD-MAS1), and maize (ZmDMAS1). Their nucleotide sequences indicate that OsDMAS1 encodes a predicted polypeptide of 318 amino acids, whereas the other three orthologs all encode predicted polypeptides of 314 amino acids and are highly homologous (82-97.5%) to each other. The DMAS proteins belong to the aldo-keto reductase superfamily 4 (AKR4) but do not fall within the existing subfamilies of AKR4 and appear to constitute a new subfamily within the AKR4 group. All of the proteins showed DMA synthesis activity in vitro. Their enzymatic activities were highest at pH 8-9, consistent with the hypothesis that DMA is synthesized in subcellular vesicles. Northern blot analysis revealed that the expression of each of the above DMAS genes is up-regulated under iron-deficient conditions in root tissue, and that of the genes OsDMAS1 and TaDMAS1 is up-regulated in shoot tissue. OsDMAS1 promoter-GUS analysis in iron-sufficient roots showed that its expression is restricted to cells participating in long distance transport and that it is highly up-regulated in the entire root under iron-deficient conditions. In shoot tissue, OsDMAS1 promoter drove expression in vascular bundles specifically under iron-deficient conditions.