Iron (Fe) is an essential micronutrient for crop productivity, but its low availability in alkaline and calcareous soils limits the growth of rice (Oryza sativa L.), which employs a combined strategy for its acquisition based on the release of phytosiderophores (PS) and the use of specific transporters. In this study, the effect of the rhizospheric bacterium Pseudomonas simiae WCS417 and the halotolerant yeast Debaryomyces hansenii CBS767 as inducers of responses to Fe deficiency in rice grown under hydroponic conditions was evaluated. Plants were inoculated in nutrient solutions with and without Fe, and PS production and the expression of genes associated with biosynthesis and transport were determined by qRT-PCR. The results showed that both microorganisms significantly increased PS production compared to controls, especially under Fe-deficient conditions, although P. simiae also exerted an effect under Fe sufficiency. Furthermore, induction of key genes (OsNAAT, OsIRO2, OsTOM1, OsYSL15, and OsIRT1), as well as genes related to the ethylene pathway (OsEIN2, OsACS2, and OsACO3), was observed, pointing to a regulatory role for this hormone in the response. In conclusion, P. simiae and D. hansenii act as inducers of Fe acquisition mechanisms in rice, offering a sustainable biotechnological approach to improve iron nutrition in limiting environments.

Coumarin-facilitated iron transport: An IRT1-independent strategy for iron acquisition in Arabidopsis thaliana

Sulphur (S) deficiency is known to hinder iron (Fe) uptake and distribution in wheat, mainly by reducing phytosiderophores (PS) synthesis and release. This study investigated the impact of S supply on Fe accumulation in four tetraploid wheat genotypes with different genetic backgrounds: a modern genotype, Svevo (Triticum turgidum subsp. durum), two ancient Khorasan wheats, Turanicum_21 and Etrusco (T. turgidum subsp. turanicum) and an ancient Polish wheat, Polonicum_2 (T.turgidum subsp. polonicum). Plants were grown hydroponically for 20 days under adequate (S = 1.2 mM) or limiting (L = 0.06 mM) sulfate levels, while receiving sufficient Fe (80 μM). Most genotypes exhibited reduced Fe accumulation under low S conditions, as expected. However, Polonicum_2 showed a unique response, accumulating significantly more Fe in both shoots and roots. This increased Fe accumulation was associated with a higher rate of PS release and upregulation of both TdYSL15 and TdIRO2 in roots of Polonicum_2, suggesting altered regulation of Fe deficiency responses. However, the expression pattern of TdIDEF1 was not correlated with TdYSL15 expression in this plant, suggesting the involvement of additional regulatory pathways beyond Fe supply. Finally, there was a strong correlation between O-acetylserine(thiol)lyase activity in shoot tissues and PS release rate across all genotypes. There is increased interest in Khorasan and Polish wheats as alternative crops for marginal areas, hence, these findings are noteworthy from a biofortification perspective and could potentially lead to innovations in agriculture that benefit food security.

The multifaceted role of YSL proteins: Iron transport and emerging functions in plant metal homeostasis.

ABSTRACTBackgroundStrategy‐II, as a response mechanism, is limited to grasses under Fe deficiency and is based on the secretion of phytosiderophores (PS) into the rhizosphere, in conjunction with the induction of a high‐affinity system for Fe(III)‐PS uptake. This strategy has a significant ecological impact and is essential for sustainable agriculture.AimsIn this work, we studied the physiological and metabolic responses of Poa pratensis L., Lolium perenne L., and Festuca rubra L. when grown in nutrient solution under Fe deficiency.MethodsAfter chlorosis appeared, we analyzed leaf pigment concentrations, biomass, and ferric chelate reductase (FCR) activity of root tips. We also screened the metabolites released by root exudates using liquid chromatography coupled to high‐resolution mass spectrometry (LC–HRMS).ResultsPlants grown with low or no Fe availability had significantly lower fresh weight (FW) and leaf chlorophyll (Chl) but higher FCR activity as compared to control plants. The root exudates contain carboxylic acids, phenolic acids, polyphenols, and peptides, among others. An increase in carboxylic acid content was correlated with Fe chlorosis in all species studied. However, the specific compounds that were upregulated varied depending on the species. Root exudates contained several upregulated metabolites that were identified as small peptides and/or peptide derivates based on their spectral data and formulas that are compatible with small peptides and/or peptide derivatives.ConclusionsThese results, together with the metal binding/chelation properties of many peptides, highlight the release of these compounds and/or their derivatives as a response of grasses to increase the Fe bioavailability.

Bacterial endophytes (120) were isolated from six halophytes (Distichlis spicata, Cynodon dactylon, Eragrostis obtusiflora, Suaeda torreyana, Kochia scoparia, and Baccharis salicifolia). These halophiles were molecularly identified and characterized with or without NaCl conditions. Characterization was based on tests such as indole acetic acid (IAA), exopolysaccharides (EPS), and siderophores (SID) production; solubilization of phosphate (P), potassium (K), zinc (Zn), and manganese (Mn); mineralization of phytate; enzymatic activity (acid and alkaline phosphatase, phytases, xylanases, and chitinases) and the mineralization/solubilization mechanisms involved (organic acids and sugars). Moreover, compatibility among bacteria was assessed. Eleven halophiles were characterized as highly tolerant to NaCl (2.5 M). The bacteria isolated were all different from each other. Two belonged to Bacillus velezensis and one to B. pumilus while the rest of bacteria were identified up to the genus level as belonging to Bacillus, Halobacillus, Halomonas, Pseudomonas, Nesterenkonia, and three strains of Oceanobacillus. The biochemical responses of nutrient solubilization and enzymatic activity were different between bacteria and were influenced by the presence of NaCl. Organic acids were involved in P mineralization and nutrient solubilization. Tartaric acid was common in the solubilization of P, Zn, and K. Maleic and vanillic acid were only detected in Zn and K solubilization, respectively. Furthermore, sugars appeared to be involved in the solubilization of nutrients; fructose was detected in the solubilization tests. Therefore, these biochemical bacterial characteristics should be corroborated in vivo and tested as a consortium to mitigate saline stress in glycophytes under a global climate change scheme that threatens to exacerbate soil salinity.

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

BackgroundCurrently, clinical laboratories lack an effective method to differentiate between classical Klebsiella pneumoniae (cKP) and hypervirulent Klebsiella pneumoniae (hvKP) strains, leading to delays in diagnosing and treating hvKP infections. Previous studies have identified peg-344, iroB, iucA, prmpA, prmpA2, and siderophores (SP) yields greater than 30 μg/ml as reliable markers for distinguishing hvKP from cKp strains. However, these diagnostic tests were conducted on a relatively small study population and lacked sufficient clinical data support. In this study, hvKP strains were identified by biomarker analysis and the Galleria mellonella model. Combined with in vitro and in vivo experiments, the reliability of clinical identification method of hvKP was verified, which provided an experimental basis for timely diagnosis of hvKP infection.ResultsAccording to the clinical data, a total of 108 strains of hvKP were preliminary screened. Among them, 94 strains were further identified using PCR analysis of biomarkers and quantitative determination of SP. The high virulence of hvKP was subsequently confirmed through infection experiments on Galleria mellonella. Additionally, susceptibility testing revealed the identification of 58 carbapenem-resistant hvKP (CR-hvKP) strains and 36 carbapenem-sensitive hvKP (CS-hvKP) strains. By comparing molecular diagnostic indexes, molecular characteristics such as high SP production of CR-hvKP were found.ConclusionThe combination of clinical data and molecular diagnostic index analysis effectively enables the identification of hvKP, particularly CR-hvKP. This study provides a scientific basis for accurate clinical identification and timely treatment of hvKP.

Phytosiderophores (PS) are root exudates released by grass species (Poaceae) that play a pivotal role in iron (Fe) plant nutrition. A direct determination of PS in biological samples is of paramount importance in understanding micronutrient acquisition mediated by PS. To date, eight plant-born PS have been identified; however, no analytical procedure is currently available to quantify all eight PS simultaneously with high analytical confidence. With access to the full set of PS standards for the first time, we report comprehensive methods to both fully characterize (IM-QTOFMS) and quantify (LC-ESI-MS/MS) all eight naturally occurring PS belonging to the mugineic acid family. The quantitative method was fully validated, yielding linear results for all eight analytes, and no unwanted interferences with soil and plant matrices were observed. LOD and LOQ values determined for each PS were below 11 and 35 nmol L−1, respectively. The method's precision under reproducibility conditions (intra- and inter-day) of measurement was less than 2.5% RSD for all analytes. Additionally, all PS were annotated with high-resolution mass spectrometric fragment spectra and further characterized via drift tube ion mobility-mass spectrometry. The collision cross-sections obtained for primary ion species yielded a valuable database for future research focused on in-depth PS studies. The new quantitative method was applied to analyse root exudates from Fe-controlled and deficient barley, oat, rye, and sorghum plants. All eight PS, including mugineic acid (MA), 3"-hydroxymugineic acid (HMA), 3"-epi-hydroxymugineic acid (epi-HMA), hydroxyavenic acid (HAVA), deoxymugineic acid (DMA), 3"-hydroxydeoxymugineic acid (HDMA), 3"-epi-hydroxydeoxymugineic acid (epi-HDMA) and avenic acid (AVA) were for the first time successfully identified and quantified in root exudates of various graminaceous plants using a single analytical procedure. These newly developed methods can be applied to studies aimed at improving crop yield and micronutrient grain content for food consumption via plant-based biofortification.

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

Siderophores produced in soil by plant growth-promoting rhizobacteria (PGPRs) play several roles, including nutrient mobilizers and can be useful as plants defense elicitors. We investigated the role of a synthetic mixed ligand bis-catechol-mono-hydroxamate siderophore (SID) that mimics the chemical structure of a natural siderophore, fimsbactin, produced by Acinetobacter spp. in the resistance against the phytopathogen Pseudomonas syringaepv tomato DC3000 (Pst DC3000), in Arabidopsis thaliana. We first tested the antibacterial activity of SID against Pst DC3000 in vitro. After confirming that SID had antibacterial activity against Pst DC3000, we tested whether the observed in vitro activity could translate into resistance of Arabidopsis to Pst DC3000, using bacterial loads as endpoints in a plant infection model. Furthermore, using quantitative polymerase chain reaction, we explored the molecular actors involved in the resistance of Arabidopsis induced by SID. Finally, to assure that SID would not interfere with PGPRs, we tested in vitro the influence of SID on the growth of a reference PGPR, Bacillus subtilis. We report here that SID is an antibacterial agent as well as an inducer of systemic priming of resistance in A. thaliana against Pst DC3000, and that SID can, at the same time, promote growth of a PGPR.

Cover Feature: Azido‐Desferrioxamine Siderophores as Functional Click‐Chemistry Probes Generated in Culture upon Adding a Diazo‐Transfer Reagent (ChemBioChem 10/2020)

In the present study, eight rhizobial strains (RH-1 to RH-8) were isolated from root nodules of cowpea which grows in acidic soils of Wayanad. They were characterized based on morphological, physiological, biochemical and molecular characteristics. The results on plant growth promoting traits showed all isolates positive to IAA production, four positive to ammonia production and five positive for in vitro siderophore production. Three isolates exhibited antagonistic activity and none of them showed volatile cyanogen production. The 16S rRNA gene sequence analysis revealed all the isolates to show similarity to Rhizobium sp. While rhizobia generally have a pH range of 6.5–7.5 for optimum growth, the isolates RH-1. RH-2, RH-4 and RH-8 grew in a liquid yeast extract-mannitol agar medium at pH-4, suggesting acid tolerance in the strain of Rhizobium. The isolates were authenticated for their nodulation and growth promotion of cowpea in a paper cup experiment and four isolates (RH-2, RH-3, RH-4 and RH-5) were evaluated for their growth promotion in cowpea under field condition. It was observed that inoculation of Rhizobium increased nodulation, growth parameters and yield of cowpea compared to uninoculated control. This study showed that these rhizobial isolates with plant growth promoting traits can be used to promote the growth and yield of cow peain acidic soils of Kerala.

Research Progress of Antibiotics Conjugated with Siderophores

Many soils of the inter-tropical regions are P-deficient because of their high fixing power and low P content. Rock phosphate resources used to produce the phosphate fertilizers are exhausted and chemical fertilizer are causing environmental degradation. This issue raised the question of sustainability of fertilization and subsequently has enhanced the interest in the use of microorganisms as biofertilizers. The aim of this study is to isolate and characterize potential P solubilizing bacteria (PSB) from two P deficient agricultural regions in Senegal. Twelve potential PSB were selected and further screened for other plant growth promoting traits (Indole-3-acetic acid (auxin) and siderophore production) and characterized by 16S rDNA sequencing. All the isolates produced auxin and seven of them produced siderophore. DNA sequencing showed that five isolates were affiliated to the genus Bacillus, four to the genus Staphylococcus, two to the genus Microbacterium and one isolate showed high similarities with members of the genus Burkholderia. The selected bacteria will further be tested on some plants to assess their biofertilization potential. Key words: 16S rDNA, indole-3-acetic-acid (IAA), phosphate solubilizing bacteria (PSB), siderophore.

Rice is staple food of nearly half the world’s population. Rice yields must therefore increase to feed ever larger populations. By colonising rice and other plants, Herbaspirillum spp. stimulate plant growth and productivity. However the molecular factors involved are largely unknown. To further explore this interaction, the transcription profiles of Nipponbare rice roots inoculated with Herbaspirillum seropedicae were determined by RNA-seq. Mapping the 104 million reads against the Oryza sativa cv. Nipponbare genome produced 65 million unique mapped reads that represented 13,840 transcripts each with at least two-times coverage. About 7.4% (1,014) genes were differentially regulated and of these 255 changed expression levels more than two times. Several of the repressed genes encoded proteins related to plant defence (e.g. a putative probenazole inducible protein), plant disease resistance as well as enzymes involved in flavonoid and isoprenoid synthesis. Genes related to the synthesis and efflux of phytosiderophores (PS) and transport of PS-iron complexes were induced by the bacteria. These data suggest that the bacterium represses the rice defence system while concomitantly activating iron uptake. Transcripts of H. seropedicae were also detected amongst which transcripts of genes involved in nitrogen fixation, cell motility and cell wall synthesis were the most expressed.

ABSTRACTWeed control based on herbicides is essential to guarantee high levels of crop productivity. However, these compounds can affect ecosystems and non-target crops. Therefore, a research was carried out in order to investigate the effect of metribuzin (ME) on the capacity of Zea mays L. (maize) to acquire iron (Fe). ME reduced the chlorophyll content, the concentration of phytosiderophores (PSs) released by roots and their Fe content. Both the shoots and roots of ME-treated plants showed increases in ammonia () concentrations. This effect was ascribed to the decreases in the activity of glutamine synthetase (GS; EC 6.3.1.2) and glutamine amide-2-oxoglutarate aminotransferase (GOGAT; EC 1.4.1.14). The results indicate that the interference exerted by ME on nitrogen organication was the cause of the drop in the PSs release and of the reduction in the Fe content.

Abstract Despite numerous studies on phytosiderophores (PS) there is still an open question whether nickel (Ni) deficiency induces release of PS from graminaceous plant roots. Seedlings of two wheat cultivars (Triticum aestivum L. cvs. Rushan and Kavir) and a triticale cultivar (X. triticosecale) were grown in Ni‐free nutrient solution (Ni‐deficient, Ni–) and with 10 µM NiSO4 (Ni‐sufficient, Ni+, control). Root exudates were collected weekly for 4 weeks and the amount of PS in the root exudates was measured. The response to Ni deficiency on the release of PS differed between species. Roots of Rushan and triticale exuded higher PS in response to Ni‐deficient conditions. Nickel deficiency significantly enhanced shoot Fe and Zn concentrations in wheat, while it decreased shoot Fe and Zn concentrations in triticale. In Kavir, PS exudation was decreased by Ni deficiency at weeks 3 and 4 and the reduced release of PS from roots of Kavir was accompanied by lower concentrations of Fe and Zn in plant roots but higher Fe and Zn concentrations in shoot tissue. The PS release by Kavir was triggered by a Ni‐induced Zn deficiency particularly in the shoots. According to the results, it is suggested that in the studies concerning the phytosiderophore release under Ni deficiency, special attention should be given to different responses among and within cereals and to the plant Zn or Fe nutritional status.

Determination of Siderophore from Bacillus Mojavensis Using Liquid Chromatography quadrupole Time-of-flight Tandem Mass Spectrometry