Iron transporter1 OsIRT1 positively regulates saline-alkaline stress tolerance in Oryza sativa.

Soil salinization-alkalization severely affects plant growth and crop yield worldwide, especially in the Songnen Plain of Northeast China. Saline-alkaline stress increases the pH around the plant roots, thereby limiting the absorption and transportation of nutrients and ions, such as iron (Fe). Fe is an essential micronutrient that plays important roles in many metabolic processes during plant growth and development, and it is acquired by the root cells via iron-regulated transporter1 (IRT1). However, the function of Oryza sativa IRT1 (OsIRT1) under soda saline-alkaline stress remains unknown. Therefore, in this study, we generated OsIRT1 mutant lines and OsIRT1-overexpressing lines in the background of the O. sativa Songjing2 cultivar to investigate the roles of OsIRT1 under soda saline-alkaline stress. The OsIRT1-overexpressing lines exhibited higher tolerance to saline-alkaline stress compared to the mutant lines during germination and seedling stages. Moreover, the expression of some saline-alkaline stress-related genes and Fe uptake and transport-related genes were altered. Furthermore, Fe and Zn contents were upregulated in the OsIRT1-overexpressing lines under saline-alkaline stress. Further analysis revealed that Fe and Zn supplementation increased the tolerance of O. sativa seedlings to saline-alkaline stress. Altogether, our results indicate that OsIRT1 plays a significant role in O. sativa by repairing the saline-alkaline stress-induced damage. Our findings provide novel insights into the role of OsIRT1 in O. sativa under soda saline-alkaline stress and suggest that OsIRT1 can serve as a potential target gene for the development of saline-alkaline stress-tolerant O. sativa plants.

Mitigating cadmium accumulation in dicotyledonous vegetables by iron fertilizer through inhibiting Fe transporter IRT1-mediated Cd uptake.

The solubility of cadmium (Cd) in soil and its transfer to plants are influenced by soil pH. While increasing soil pH reduces Cd solubility and accumulation in rice plants grown in acidic soils, its effect on Cd accumulation in vegetables remains inconclusive. Here, we investigated the impact of soil pH on Cd accumulation in dicotyledonous vegetables and elucidated the underlying molecular mechanisms. Soils collected from various locations were supplemented with varying quantities of lime to achieve soil pH values of around 5.0, 6.0, 7.0, and 8.0. Raising soil pH from around 5.0 to 8.0 markedly decreased extractable Cd. However, increasing soil pH tended to promote shoot Cd accumulation in dicotyledonous vegetable species including lettuce, pakchoi, and Chinese cabbage, and the model dicotyledonous plant Arabidopsis thaliana. Conversely, soil pH increase resulted in a monotonic decrease in rice Cd accumulation. In our hydroponic experiments, we discovered that iron (Fe) deficiency substantially increased Cd uptake and accumulation in dicotyledonous plants but not in rice. Increasing soil pH reduced soil Fe availability and induced the Fe transporter gene IRT1 expression in dicotyledonous vegetables roots, which led to an increase in IRT1-mediated Cd uptake and subsequently increased Cd accumulation as soil pH increases. A comprehensive model incorporating extractable Cd and root IRT1 expression better explained Cd accumulation in vegetable shoots. The application of 50 mg/kg of Fe fertilizer in neutral or alkaline soils resulted in a significant reduction in Cd accumulation by 34-58% in dicotyledonous vegetables. These findings reveal that increasing soil pH has two opposite effects, decreasing soil Cd availability while promoting Cd uptake through IRT1 upregulation, reconciling the inconsistency in its effect on Cd accumulation in dicotyledonous plants. Our findings provide important insights for understanding the factors affecting Cd uptake in plants and offer a practical solution to mitigate Cd contamination in vegetables.

The Distinguishing Factor in Soccer Players is Aerobic Performance, not the ACTN3 Gene / El Factor Distintivo en los Jugadores de Fútbol es el Rendimiento Aeróbico y no el gen ACTN3

SUMMARY: The purpose of this study was to reveal the differences between ACTN3 genotype (RR, RX, XX) and aerobic performance [Yo-Yo IRT1 (m), VO2 max (ml/kg/min)] in professional and regional amateur league soccer players and to reveal which of these parameters was a distinctive factor in these athletes.71 professional soccer players (age: 23.66 ± 4.11 years; body height: 1.79 ± 6.99 m; body weight: 76.02 ± 6.76 kg; body fat: 11.59±3.11 %) and 62 regional amateur soccer players (age: 23.63 ±3.77 years; body height: 1.81 ± 5.77 m; body weight: 76.36 ± 7.53 kg; body fat: 15.60±4.65 %) volunteered for the study. After DNA extraction from buccal epithelial cells via a commercial kit was performed for the genetic background of the athletes, Real-Time PCR was carried out for genotyping. Furthermore, Yo-Yo IRT1 test was performed to determine the aerobic performance of the soccer players. SPSS 23 (SPSS Inc., Chicago, IL, USA) package program was used for the statistical analysis of the data obtained in the tests. Shapiro-Wilk test for normality and Levene's test for homogeneity of variance were performed. Chi-Square, Independent Sample T Test and One Way ANOVA test were used in the analysis of the parameters. Statistical significance was set as p0.05); however, there was a statistical significance in favor of professional soccer players in terms of aerobic parameters (p<0.05). Consequently, it can be said that aerobic performance is the distinguishing factor, not the ACTN3 gene, in soccer players.

El objetivo de este estudio fue revelar las diferencias entre el genotipo ACTN3 (RR, RX, XX) y el rendimiento aeróbico [Yo-Yo IRT1 (m), VO2 max (ml/kg/min)] en jugadores de fútbol de ligas profesionales y amateurs regionales y determinar cuál de estos parámetros es un factor distintivo en estos deportistas. 71 futbolistas profesionales (edad: 23,66 ±4,11 años; altura corporal: 1,79 ± 6,99 m; peso corporal: 76,02 ± 6,76 kg; grasa corporal: 11,59±3,11 %) y 62 jugadores de fútbol amateur regionales (edad: 23,63 ± 3,77 años; altura corporal: 1,81 ± 5,77 m; peso corporal: 76,36 ± 7,53 kg; grasa corporal: 15,60 ± 4,65 %) se ofrecieron como voluntarios para el estudio. Después de realizar la extracción de ADN de las células epiteliales orales mediante un kit comercial para obtener los antecedentes genéticos de los atletas, se llevó a cabo una PCR en tiempo real para el genotipado. Además, se realizó la prueba Yo-Yo IRT1 para determinar el rendimiento aeróbico de los futbolistas. Para el análisis estadístico de los datos obtenidos en las pruebas se utilizó el programa SPSS 23 (SPSS Inc., Chicago, IL, EE. UU.). Se realizó la prueba de normalidad de Shapiro- Wilk y la prueba de homogeneidad de la varianza de Levene. En el análisis de los parámetros se utilizaron Chi-cuadrado, prueba T para muestra independiente y prueba ANOVA unidireccional. La significancia estadística se estableció en p0,05); sin embargo, hubo significación estadística a favor de los futbolistas profesionales en cuanto a los parámetros aeróbicos (p<0,05). En consecuencia, se puede decir que el rendimiento aeróbico es el factor distintivo, no el gen ACTN3, en los jugadores de fútbol.

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

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

Regulatory module WRKY33-ATL31-IRT1 mediates cadmium tolerance in Arabidopsis.

Cadmium (Cd) is one of the most dangerous environmental pollutants among heavy metals, and threatens food safety and human health by accumulating in plant sink tissues. Here, we report a novel regulatory cascade that profoundly influences Cd tolerance in Arabidopsis. Phenotypic analysis showed that an insertional knockdown mutation at the Arabidopsis Tóxicos en Levadura 31 (ATL31) locus resulted in hypersensitivity to Cd stress, most likely due to a significant increase in Cd accumulation. Consistently, ATL31-overexpressing lines exhibited enhanced Cd stress tolerance and reduced Cd accumulation. Further, IRON-REGULATED TRANSPORTER 1 (IRT1) was identified, and yeast two-hybrid, co-immunoprecipitation and bimolecular fluorescence complementation assays demonstrated its interaction with ATL31. Biochemical, molecular, and genetic analyses showed that IRT1 is targeted by ATL31 for ubiquitin-conjugated degradation in response to Cd stress. Intriguingly, transcription of ATL31 was strongly induced by Cd stress. In addition, transgenic and molecular analyses showed that WRKY33 directly activated the transcription of ATL31 in response to Cd stress and positively regulated Cd tolerance. Genetic analysis indicated that ATL31 acts upstream of IRT1 and downstream of WRKY33 to regulate Cd tolerance. Our study revealed that the WRKY33-ATL31-IRT1 module plays a crucial role in timely blocking Cd absorption to prevent metal toxicity in Arabidopsis.

The overexpression of LOW PHOSPHATE ROOT 1 (LPR1) negatively regulates Arabidopsis growth in response to Cadmium (Cd) stress.

Cadmium (Cd) is a highly toxic element that is easily absorbed by plant, and the mechanisms of the plant response to Cd toxicity are very complex. In this study, the role of LPR1 (LOW Phosphate Root 1) encoding a cell-wall-targeted ferroxidase in Cd stress was investigated. The results showed that the overexpression of LPR1 caused an average reduction of 23%-40% in the primary root lengths, 67%-73% in the fresh weights, 32%-46% in the lengths of the non-root hair zone (NRHZ) and 70%-71% in the chlorophyll contents in both LPR1-OX lines when compared with the wild type (WT), while there were no significant changes in these traits between the WT and mutant lpr1 lines under Cd stress (7.5 µmol/L CdSO4). Further investigation showed that the overexpression of LPR1 triggered reactive oxygen species (ROS) bursts and reduced the entry of available iron (Fe2+) into the cell, which induced the expression of iron-regulated transporter 1 (IRT1). The up-regulation of IRT1 contributed to the increase of Cd accumulation and growth retardation under Cd stress. Exogenous Fe and ROS scavengers down-regulated the IRT1's expression and alleviated the growth inhibition in LPR1-OX lines, indicating that LPR1-dependent ROS up-regulated IRT1, which subsequently exacerbated the Cd influx into plants. Our findings highlight a pathway of LPR1-mediated plant responding to Cd toxicity stress through the regulation of ROS and Fe homeostasis.

Establishment of hairy root system of transgenic IRT1 brassica campestris L. and preliminary study of its effect on cadmium enrichment.

Cadmium (Cd) is the main heavy metal pollutant in soil. The combination of genetic engineering technology and Rizobium rhizogenes mediated technology can effectively improve the enrichment efficiency of heavy metals in super accumulators and reduce soil heavy metal pollution. In this study, the transgenic hairy root system containing the IRT1 gene of Cd hyperaccumulator-Brassica campestris L. was successfully constructed by the R. rhizogenes mediated method (IRT1 gene come from Arabidopsis thaliana). The hairy roots of each subculture can grow stably within 6 weeks, and IRT1 gene will not be lost within 50 subcultures., which is detected using PCR method. The results of Cd enrichment experiments showed that after treatment with 100 µmol/L Cd for 14 days, the growth state of transgenic IRT1 hairy roots only showed slight browning. Also, the accumulation value of Cd reached 331.61 µg/g and the enrichment efficiency of transgenic IRT1 hairy roots was 13.8% higher than that of wild-type hairy roots. Western blotting results showed that the expression of IRT1 protein in transgenic hairy roots was significantly higher than that of wild-type hairy roots under Cd stress. The above results indicated that the overexpression of IRT1 gene can help B. campestris L. hairy roots to effectively cope with Cd stress and improve its ability to enrich Cd.

In this study, the transgenic hairy root system containing the IRT1 gene of Cd hyperaccumulator-Brassica campestris L. was successfully constructed by the Rizobium rhizogenes mediated method. At the same time, the growth state and cadmium enrichment efficiency of transgenic hairy roots under different concentrations of Cd stress were studied. Overexpression of IRT1 gene can effectively improve the tolerance of hairy root to Cd. The enrichment efficiency of transgenic IRT1 hairy roots was 13.8% higher than that of wild-type hairy roots. The transgenic IRT1 hairy root system established in this study can be used as a reliable experimental model for the study of Cd adsorption mechanism, and can be further regenerated to obtain transgenic IRT1 B. campestris L. plants for the study of heavy metal Cd pollution remediation.

Ferrous iron uptake via IRT1/ZIP evolved at least twice in green plants.

Iron (Fe) is essential for virtually all organisms, being irreplaceable because of its electrochemical properties that enable many biochemical processes, including photosynthesis. Besides its abundance, Fe is generally found in the poorly soluble form of ferric iron (Fe3+ ), while most plants uptake the soluble form Fe2+ . The model angiosperm Arabidopsis thaliana, for example, captures Fe through a mechanism that lowers rhizosphere pH through proton pumping that increases Fe3+ solubility, which is then reduced by a membrane-bound reductase and transported into the cell by the zinc-regulated, iron-regulated transporter-like protein (ZIP) family protein AtIRT1. ZIP proteins are transmembrane transporters of divalent metals such as Fe2+ , Zn2+ , Mn2+ , and Cd2+ . In this work, we investigated the evolution of functional homologs of IRON-REGULATED TRANSPORTER 1/ZIP in the supergroup Archaeplastida (Viridiplantae + Rhodophyta + Glaucophyta) using 51 genomes of diverse lineages. Our analyses suggest that Fe is acquired through deeply divergent ZIP proteins in land plants and chlorophyte green algae, indicating that Fe2+ uptake by ZIP proteins evolved independently at least twice throughout green plant evolution. Our results indicate that the archetypical IRON-REGULATED TRANSPORTER (IRT) proteins from angiosperms likely emerged before the origin of land plants during early streptophyte algae terrestrialization, a process that required the evolution of Fe acquisition in terrestrial subaerial settings.

Birth, life and death of the Arabidopsis IRT1 iron transporter: the role of close friends and foes.

MAIN CONCLUSION: IRT1 intracellular dynamics and function are finely controlled through protein-protein interactions. In plants, iron uptake from the soil is tightly regulated to allow optimal growth and development. Iron acquisition in Arabidopsis root epidermal cells requires the IRT1 transporter, which also mediates the entry of non-iron metals. In this mini-review, we describe how protein-protein interactions regulate IRT1 intracellular dynamics and IRT1-mediated metal uptake to maintain iron homeostasis. Recent interactomic data provided interesting clues on IRT1 secretion and the putative involvement of COPI- and COPII-mediated pathways. Once delivered to the plasma membrane, IRT1 can interact with other components of the iron uptake machinery to form an iron acquisition complex that likely optimizes iron entrance in root epidermal cells. Then, IRT1 may be internalized from the plasma membrane. In the past decade, IRT1 endocytosis emerged as an essential mechanism to control IRT1 subcellular localization and thus to tune iron uptake. Interestingly, IRT1 endocytosis and degradation are regulated by its non-iron metal substrates in an ubiquitin-dependent manner, which requires a set of interacting-proteins including kinases, E3 ubiquitin ligases and ESCRT complex subunits. This mechanism is essential to avoid non-iron metal overload in Arabidopsis when the iron is scarce.

Differential metal sensing and metal-dependent degradation of the broad spectrum root metal transporter IRT1.

Iron is an essential micronutrient for plant growth and development. Under low iron conditions, Arabidopsis plants take up soil iron using the root iron transporter IRT1. In addition to iron, IRT1 also transports others divalent metals, including cadmium, which consequently accumulates into plant tissues and enters the food chain. IRT1 expression was shown to be regulated at the transcriptional and post-translational levels by its essential metal substrates to maximize iron uptake while limiting the accumulation of zinc, manganese, or cobalt. Here, we characterized the regulation of IRT1 by cadmium. A short-term exposure to cadmium decreased the cell surface levels of IRT1 through endocytosis and degradation, but with a lower efficiency than observed for other IRT1 metal substrates. We demonstrated that IRT1 endocytosis in response to cadmium is mediated through the direct binding of cadmium to histidine residues within the regulatory loop of IRT1. However, we revealed that the affinity of the metal sensing motif is much lower for cadmium compared to other metal substrates of IRT1. Finally, we proved that cadmium-induced IRT1 degradation takes place through ubiquitin-mediated endocytosis driven by the UBC35/36 E2 ubiquitin-conjugating enzymes and the IDF1 E3 ubiquitin ligase. Altogether, this work sheds light on the mechanisms of cadmium-mediated downregulation of IRT1 and provides an additional molecular basis for cadmium accumulation and toxicity in plants.

Different pathways for exogenous ABA-mediated down-regulation of cadmium accumulation in plants under different iron supplies.

Exogenous abscisic acid (ABA) could inhibit cadmium (Cd) accumulation in plants; however, its performance in an uneven iron (Fe) background remains unknown. Here, we found that the inhibitory effects of ABA on Cd accumulation in plants were optimal under nonlimiting Fe availability (25 and 50 µM), causing a reduction of 25-50 %, whereas only a 0-29 % decrease was observed in a Fe-free or -deficient (5 µM) medium. Although ABA significantly inhibited the expression of IRT1 under different Fe supplies, the inhibitory effects of ABA on Cd accumulation were lower (or absent) in irt1-mutants than in wild-type plants growing under nonlimiting Fe availability, whereas no significant difference was found under Fe deficiency. The mechanisms by which ABA reduces Cd accumulation under different Fe environments may differ. Furthermore, under Fe sufficiency, ABA increased Fe levels of root apoplasts by 91 % without changing the activity level of root ferric reductase (FCR). In contrast, ABA resulted in a 17 % decrease in Fe concentration in apoplasts and a 37 % decrease in FCR activity under Fe-deficient conditions. Thus, under Fe sufficiency, plants may show a reduced accumulation of Cd by accumulating more Fe in the apoplasts, which in turn inhibits the expression of IRT1. However, plants are more prone to redirect apoplastic Fe to prevent Cd accumulation under Fe deficiency. The different mechanisms of inhibition of Cd accumulation by ABA under different Fe supplies revealed in this study may provide guidelines for the precise regulation of Cd accumulation in crops via ABA-based strategies.

TpIRT1 from Polish wheat (Triticum polonicum L.) enhances the accumulation of Fe, Mn, Co, and Cd in Arabidopsis.

Uptake and internal transport of micronutrients are essential for plant growth, development, and yield. In this regard, Iron Regulated Transporters (IRTs) from the Zinc Regulated Transporter (ZRT)/IRT-related protein (ZIP) family play an important role in transition metal uptake. Most studies have been focused on IRT1-like proteins in diploid species. Information on IRT1-like proteins in polyploids is limited. Here, we studied the function of TpIRT1A and TpIRT1B homoeologs in a tetraploid crop, Polish wheat (Triticum polonicum L.). Our results highlighted the importance of TpIRT1 in mediating the uptake and translocation of Fe, Mn, Co, and Cd with direct implications for wheat yield potential. Both TpIRT1A and TpIRT1B were located at the plasma membrane and internal vesicle-like organelle in protoplasts of Arabidopsis thaliana L. and increased Cd and Co sensitivity in yeast. The over-expression of TpIRT1B in A. thaliana increased Fe, Mn, Co, and Cd concentration in its tissues and improved plant growth under Fe, Mn, and Co deficiencies, while increased the sensitivity to Cd compared to wild type. Functional analysis of IRT1 homoeologs from tetraploid and diploid ancestral wheat species in yeast disclosed four distinct amino acid residues in TdiIRT1B (T. dicoccum L. (Schrank)) and TtuIRT1B (T. turgidum L.). Together, our results increase the knowledge of IRT1 function in a globally important crop, wheat.

Fe acquisition at the crossroad of calcium and reactive oxygen species signaling.

Due to its redox properties, iron is both essential and toxic. Therefore, soil iron availability variations pose a significant problem for plants. Recent evidence suggests that calcium and reactive oxygen species coordinate signaling events related to soil iron acquisition. Calcium was found to affect directly IRT1-mediated iron import through the lipid-binding protein EHB1 and to trigger a CBL-CIPK-mediated signaling influencing the activity of the key iron-acquisition transcription factor FIT. In parallel, under prolonged iron deficiency, reactive oxygen species both inhibit FIT function and depend on FIT through the function of the catalase CAT2. We discuss the role of calcium and reactive oxygen species signaling in iron acquisition, with post-translational mechanisms influencing the localization and activity of iron-acquisition regulators and effectors.

The effect of endophytic fungi on growth and nickel accumulation in Noccaea hyperaccumulators.

The role of endophytic fungi isolated from different populations of European Ni hyperaccumulators was investigated in regard to the microorganisms' ability to enhance the hyperaccumulation of Ni in Noccaea caerulescens. Effects of particular species of endophytic fungi on adaptation of N. caerulescens to excess Ni were tested by co-cultivation with single strains of the fungi. Seven of these had a positive effect on plant biomass production, whereas two of the tested species inhibited plant growth; biomass production of inoculated plants was significantly different compared to non-inoculated control. Inoculation with six fungal strains: Embellisia thlaspis, Pyrenochaeta cava, Phomopsis columnaris, Plectosphaerella cucumerina, Cladosporium cladosporioides and Alternaria sp. stimulated the plant to uptake and accumulate more Ni in both roots and shoots, compared to non-inoculated control. P. columnaris was isolated from all plant species sampled. Strains isolated from Noccaea caerulescens and Noccaea goesingensis increased Ni root and shoot accumulation of their native hosts (compared to non-inoculated control). Inoculation of different populations of Noccaea with P. columnaris of foreign origin did not cause its host to accumulate more Ni, with the exception of the Ni-unadapted ecotype of N. goesingensis. Inoculation with P. columnaris from N. caerulescens significantly improved Ni uptake, but the effect of the fungus was not as prominent as in the case of N. caerulescens. By comparing the transcriptomes of N. caerulescens and N. goesingensis from Flatz inoculated with P. columnaris, we showed that enhanced uptake and accumulation of Ni in the plants is accompanied by an upregulation of several genes mainly involved in plant stress protection and metal uptake and compartmentation.

Endocytosis in plants: Peculiarities and roles in the regulated trafficking of plant metal transporters.

The removal of transmembrane proteins from the plasma membrane via endocytosis has emerged as powerful strategy in the regulation of receptor signalling and molecule transport. In the last decade, IRON-REGULATED TRANSPORTER1 (IRT1) has been established as one of the key plant model proteins for studying endomembrane trafficking. The use of IRT1 and additional other metal transporters has uncovered novel factors involved in plant endocytosis and facilitated a better understanding of the role of endocytosis in the fine balancing of plant metal homoeostasis. In this review, we outline the specifics of plant endocytosis compared to what is known in yeast and mammals, and based on several examples, we demonstrate how studying metal transport has contributed to extending our knowledge of endocytic trafficking by shedding light on novel regulatory mechanisms and factors.

Melatonin alleviates cadmium toxicity by reducing nitric oxide accumulation and IRT1 expression in Chinese cabbage seedlings.

Melatonin (MT) is reported as a kind of phytohormone, exerts various biological activities, mediating plant growth and development and responding to abiotic stresses. In the present research, we examined the possibility that MT could involve in the alleviation of cadmium (Cd) toxicity by reducing the accumulation of nitric oxide (NO). The research indicated that the addition of MT significantly increased the biomass and photosynthetic parameters of plants compared with the control treated under Cd stress. Besides, we found that compared with the control treatment, MT also reduced the level of Cd-induced nitric oxide, and at the same time, the enzyme activity related to NO synthesis and the expression of related genes were decreased. In addition, MT treatment significantly reduced the Cd content in Chinese cabbage seedlings compared with the control, which was partially reversed by the addition of SNP (NO donor). PTIO (NO scavenger) addition could reduce the Cd content when seedlings were exposed to Cd stress. At the same time, compared with the Cd stress, the concentration of Cd in MT-treated plants decreased significantly, and the expression levels of related transport genes IRT1 also decreased significantly. Taken together, these results further support the idea that under the stress of Cd, NO increases the expression of IRT1, thus further increasing the absorption of Cd and aggravating the stress of Cd in plants, while exogenously added MT can inhibit the synthesis of NO, reduce the content of Cd, and alleviate the stress caused by Cd.

Iron deficiency triggered transcriptome changes in bread wheat.

A series of complex transport, storage and regulation mechanisms control iron metabolism and thereby maintain iron homeostasis in plants. Despite several studies on iron deficiency responses in different plant species, these mechanisms remain unclear in the allohexaploid wheat, which is the most widely cultivated commercial crop. We used RNA sequencing to reveal transcriptomic changes in the wheat flag leaves and roots, when subjected to iron limited conditions. We identified 5969 and 2591 differentially expressed genes (DEGs) in the flag leaves and roots, respectively. Genes involved in the synthesis of iron ligands i.e., nicotianamine (NA) and deoxymugineic acid (DMA) were significantly up-regulated during iron deficiency. In total, 337 and 635 genes encoding transporters exhibited altered expression in roots and flag leaves, respectively. Several genes related to MAJOR FACILITATOR SUPERFAMILY (MFS), ATP-BINDING CASSETTE (ABC) transporter superfamily, NATURAL RESISTANCE ASSOCIATED MACROPHAGE PROTEIN (NRAMP) family and OLIGOPEPTIDE TRANSPORTER (OPT) family were regulated, indicating their important roles in combating iron deficiency stress. Among the regulatory factors, the genes encoding for transcription factors of BASIC HELIX-LOOP-HELIX (bHLH) family were highly up-regulated in both roots and the flag leaves. The jasmonate biosynthesis pathway was significantly altered but with notable expression differences between roots and flag leaves. Homoeologs expression and induction bias analysis revealed subgenome specific differential expression. Our findings provide an integrated overview on regulated molecular processes in response to iron deficiency stress in wheat. This information could potentially serve as a guideline for breeding iron deficiency stress tolerant crops as well as for designing appropriate wheat iron biofortification strategies.

Phospho-mutant activity assays provide evidence for alternative phospho-regulation pathways of the transcription factor FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR.

The key basic helix-loop-helix (bHLH) transcription factor in iron (Fe) uptake, FER-LIKE IRON DEFICIENCY-INDUCED TRANSCRIPTION FACTOR (FIT), is controlled by multiple signaling pathways, important to adjust Fe acquisition to growth and environmental constraints. FIT protein exists in active and inactive protein pools, and phosphorylation of serine Ser272 in the C-terminus, a regulatory domain of FIT, provides a trigger for FIT activation. Here, we use phospho-mutant activity assays and study phospho-mimicking and phospho-dead mutations of three additional predicted phosphorylation sites, namely at Ser221 and at tyrosines Tyr238 and Tyr278, besides Ser 272. Phospho-mutations at these sites affect FIT activities in yeast, plant, and mammalian cells. The diverse array of cellular phenotypes is seen at the level of cellular localization, nuclear mobility, homodimerization, and dimerization with the FIT-activating partner bHLH039, promoter transactivation, and protein stability. Phospho-mimicking Tyr mutations of FIT disturb fit mutant plant complementation. Taken together, we provide evidence that FIT is activated through Ser and deactivated through Tyr site phosphorylation. We therefore propose that FIT activity is regulated by alternative phosphorylation pathways.

The bifunctional transporter-receptor IRT1 at the heart of metal sensing and signalling.

Transporters are at the centre of regulatory modules allowing optimal assimilation, distribution or efflux of substrate molecules. The IRT1 root metal transporter represents a textbook example in which detailed regulatory networks have been shown to integrate several endogenous and exogenous cues at various levels to regulate its expression and to fine tune iron uptake. Here, we summarise recent advances in the dissection of the transcriptional and posttranslational control of IRT1 by its various metals substrates and discuss the emerging role of IRT1 in the direct sensing of non-iron metals flowing through IRT1 to drive its degradation. We propose that transporters that also act as receptors are likely to be a common theme in the regulation of nutrient transport by sensing local nutrient concentrations.