Iron Homeostasis in Rice: Deficit and Excess

Soil and Mineral Nutrients in Plant Health: A Prospective Study of Iron and Phosphorus in the Growth and Development of Plants

Plants being sessile are exposed to different environmental challenges and consequent stresses associated with them. With the prerequisite of minerals for growth and development, they coordinate their mobilization from the soil through their roots. Phosphorus (P) and iron (Fe) are macro- and micronutrient; P serves as an important component of biological macromolecules, besides driving major cellular processes, including photosynthesis and respiration, and Fe performs the function as a cofactor for enzymes of vital metabolic pathways. These minerals help in maintaining plant vigor via alterations in the pH, nutrient content, release of exudates at the root surface, changing dynamics of root microbial population, and modulation of the activity of redox enzymes. Despite this, their low solubility and relative immobilization in soil make them inaccessible for utilization by plants. Moreover, plants have evolved distinct mechanisms to cope with these stresses and coregulate the levels of minerals (Fe, P, etc.) toward the maintenance of homeostasis. The present study aims at examining the uptake mechanisms of Fe and P, and their translocation, storage, and role in executing different cellular processes in plants. It also summarizes the toxicological aspects of these minerals in terms of their effects on germination, nutrient uptake, plant-water relationship, and overall yield. Considered as an important and indispensable component of sustainable agriculture, a separate section covers the current knowledge on the cross-talk between Fe and P and integrates complete and balanced information of their effect on plant hormone levels.

Deciphering the regulation of transporters and mitogen-activated protein kinase in arsenic and iron exposed rice

This study investigates the influence of arsenic (As) and iron (Fe) on the molecular aspects of rice plants. The mRNA-abundance of As (OsLsi, OsPHT, OsNRAMP1, OsABCC1) and Fe (OsIRT, OsNRAMP1, OsYSL, OsFRDL1, OsVIT2, OsSAMS1, OsNAS, OsNAAT1, OsDMAS1, OsTOM1, OsFER) related genes has been observed in 12-d old As and Fe impacted rice varieties. Analyses of phytosiderophores synthesis and Fe-uptake genes affirm the existence of specialized Fe-uptake strategies in rice with varieties PB-1 and Varsha favouring strategy I and II, respectively. Expression of OsNAS3, OsVIT2, OsFER and OsABCC1 indicated PB-1's tolerance towards Fe and As. Analysis of mitogen-activated protein kinase cascade members (OsMKK3, OsMKK4, OsMKK6, OsMPK3, OsMPK4, OsMPK7, and OsMPK14) revealed their importance in the fine adjustment of As/Fe in the rice system. A conditional network map was generated based on the gene expression pattern that unfolded the differential dynamics of both rice varieties. The mating based split ubiquitin system determined the interaction of OsIRT1 with OsMPK3, and OsLsi1 with both OsMPK3 and OsMPK4. In-silico tools also confirmed the binding affinities of OsARM1 with OsLsi1, OsMPK3 and OsMPK4, and of OsIDEF1/OsIRO2 with OsIRT1 and OsMPK3, supporting our hypothesis that OsARM1, OsIDEF1, OsIRO2 were active in the connections discovered by mbSUS.

Iron (Fe) toxicity, uptake, translocation, and physio-morphological responses in Catharanthus roseus

Iron (Fe) toxicity in plant species depends on the availability of Fe in the soil, uptake ability by the root system, and translocation rate to other parts of the plant. The aim of this study was to assess Fe uptake by root tissues of Catharanthus roseus, translocation rate to leaf tissues, and the impairment of plant physio-morphological characteristics. Fe uptake by the roots (~ 700 µg g-1 DW) of C. roseus was observed during the early exposure period (1 week), and translocation factor from root to shoot was fluctuated as an independent strategy. A high level of Fe content in the root tissues significantly inhibited root length and root dry weight. Under acidic pH condition, an enrichment of Fe in the shoots (~ 400 µg g-1 DW) led to increase in leaf temperature (> 2.5 °C compared to control) and crop stress index (> 0.6), resulting in stomatal closure, subsequently decreasing CO2 assimilation rate and H2O transpiration rate. An increment of CSI in Fe-stressed plants was negatively related to stomatal conductance, indicating stomatal closure with an increase in Fe in the leaf tissues. High Fe levels in the leaf tissues directly induced toxic symptoms including leaf bronzing, leaf spotting, leaf necrosis, leaf chlorosis, and leaf senescence in C. roseus plants. In summary, C. roseus was identified as a good candidate plant for Fe phytoextraction, depending on Fe bioaccumulation, therefore 50 mM Fe treatment was designated as an excess Fe to cause the growth inhibition, especially in the prolonged Fe incubation periods.

Graphical abstract

Supplementary Information

The online version contains supplementary material available at 10.1007/s12298-023-01379-5.

Understanding the Mechanisms of Fe Deficiency in the Rhizosphere to Promote Plant Resilience

One of the most significant constraints on agricultural productivity is the low availability of iron (Fe) in soil, which is directly related to biological, physical, and chemical activities in the rhizosphere. The rhizosphere has a high iron requirement due to plant absorption and microorganism density. Plant roots and microbes in the rhizosphere play a significant role in promoting plant iron (Fe) uptake, which impacts plant development and physiology by influencing nutritional, biochemical, and soil components. The concentration of iron accessible to these live organisms in most cultivated soil is quite low due to its solubility being limited by stable oxyhydroxide, hydroxide, and oxides. The dissolution and solubility rates of iron are also significantly affected by soil pH, microbial population, organic matter content, redox processes, and particle size of the soil. In Fe-limiting situations, plants and soil microbes have used active strategies such as acidification, chelation, and reduction, which have an important role to play in enhancing soil iron availability to plants. In response to iron deficiency, plant and soil organisms produce organic (carbohydrates, amino acids, organic acids, phytosiderophores, microbial siderophores, and phenolics) and inorganic (protons) chemicals in the rhizosphere to improve the solubility of poorly accessible Fe pools. The investigation of iron-mediated associations among plants and microorganisms influences plant development and health, providing a distinctive prospect to further our understanding of rhizosphere ecology and iron dynamics. This review clarifies current knowledge of the intricate dynamics of iron with the end goal of presenting an overview of the rhizosphere mechanisms that are involved in the uptake of iron by plants and microorganisms.

The rhizosphere bacterial community contributes to the nutritional competitive advantage of weedy rice over cultivated rice in paddy soil

Background

Weedy rice competes for nutrients and living space with cultivated rice, which results in serious reductions in rice production. The rhizosphere bacterial community plays an important role in nutrient competition between species. It is therefore important to clarify the differences in the diversities of the inter rhizosphere bacterial community between cultivated rice and weedy rice. The differences in compositions and co-occurrence networks of the rhizosphere bacterial community of cultivated rice and weedy rice are largely unknown and thus the aim of our study.

Results

In our study, the different rhizosphere bacterial community structures in weedy rice (AW), cultivated rice (AY) and cultivated rice surrounded by weedy rice (WY) were determined based on 16S rRNA gene sequencing. The majority of the WY rhizosphere was enriched with unique types of microorganisms belonging to Burkholderia. The rhizosphere bacterial community showed differences in relative abundance among the three groups. Network analysis revealed a more complex co-occurrence network structure in the rhizosphere bacterial community of AW than in those of AY and WY due to a higher degree of Microbacteriaceae and Micrococcaceae in the network. Both network analysis and functional predictions reveal that weedy rice contamination dramatically impacts the iron respiration of the rhizosphere bacterial community of cultivated rice.

Conclusions

Our study shows that there are many differences in the rhizosphere bacterial community of weedy rice and cultivated rice. When cultivated rice was disturbed by weedy rice, the rhizosphere bacterial community and co-occurrence network also changed. The above differences tend to lead to a nutritional competitive advantage for weedy rice in paddy soils.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12866-022-02648-1.

An insight into the act of iron to impede arsenic toxicity in paddy agro-system

Surplus research on the widespread arsenic (As) revealed its disturbing role in obstructing the metabolic function of plants. Also, the predilection of As towards rice has been an interesting topic. Contrary to As, iron (Fe) is an essential micronutrient for all life forms. Past findings propound about the enhanced As-resistance in rice plants during Fe supplementation. Thus, considering the severity of As contamination and resulting exposure through rice crops, as well as the studied cross-talks between As and Fe, we found this topic of relevance. Keeping these in view, we bring this review discussing the presence of As-Fe in the paddy environment, the criticality of Fe plaque in As sequestration, and the effectiveness of various Fe forms to overcome As toxicity in rice. This type of interactive analysis for As and Fe is also crucial in the context of the involvement of Fe in cellular redox activities such as oxidative stress. Also, this piece of work highlights Fe biofortification approaches for better rice varieties with optimum intrinsic Fe and limited As. Though elaborated by others, we lastly present the acquisition and transport mechanisms of both As and Fe in rice tissues. Altogether we suggest that Fe supply and Fe plaque might be a prospective agronomical tool against As poisoning and for phytostabilization, respectively.

In silico analysis of comparative affinity of phytosiderophore and bacillibactin for iron uptake by YSL15 and YSL18 receptors of Oryza sativa

Iron is an important micronutrient for plant growth and development. In the case of Oryza sativa, iron is made available primarily with the help of iron chelators called phytosiderophores i.e. variants of deoxymugineic acid (DMA). They bind with ferric ions and get internalized through Yellow Stripe Like transporters viz. YSL15 and YSL18. However, due to low amount of secretion of phytosiderophores, rice suffers from iron deficiency. Alternatively, siderophores of plant growth promoting rhizobacteria may support iron uptake and make it available to plants via transporting ferric ions possibly through the same transporters. Present study aims to assess comparative binding of DMA and a xenosiderophore (siderophores used by organisms other than the ones producing them) of rhizobacteria i.e. bacillibactin with Fe³⁺ ion and subsequent transporters of rice. Protein-protein interaction and gene expression analysis predicts uptake of Fe³⁺ by YSL15 from the rhizosphere region and further distribution through YSL18 with the help of various predicted functional partners. Docking studies confirm the thermodynamically more favourable structure of bacillibactin-Fe³⁺ complex than DMA-Fe³⁺ complex. Molecular modelling of YSL15 and YSL18 was done through ab initio method and their evaluation by Ramachandran plot, ProSA, ERRAT value and verify 3 D score revealed a good quality models. Comparative binding assessment through docking and molecular dynamics simulation suggests better binding energies of YSL transporters with bacillibactin-Fe³⁺ complex as compared to DMA-Fe³⁺ complex. The current study suggests possible application of xenosiderophores of PGPR origin in supporting plant growth via iron uptake and distribution in rice.Communicated by Ramaswamy H. Sarma.

Genetic biofortification of wheat with zinc: Opportunities to fine-tune zinc uptake, transport and grain loading

Zinc (Zn) is an important micronutrient in the human body, and health complications associated with insufficient dietary intake of Zn can be overcome by increasing the bioavailable concentrations in edible parts of crops (biofortification). Wheat (Triticum aestivum L) is the most consumed cereal crop in the world; therefore, it is an excellent target for Zn biofortification programs. Knowledge of the physiological and molecular processes that regulate Zn concentration in the wheat grain is restricted, inhibiting the success of genetic Zn biofortification programs. This review helps break this nexus by advancing understanding of those processes, including speciation regulated uptake, root to shoot transport, remobilisation, grain loading and distribution of Zn in wheat grain. Furthermore, new insights to genetic Zn biofortification of wheat are discussed, and where data are limited, we draw upon information for other cereals and Fe distribution. We identify the loading and distribution of Zn in grain as major bottlenecks for biofortification, recognising anatomical barriers in the vascular region at the base of the grain, and physiological and molecular restrictions localised in the crease region as major limitations. Movement of Zn from the endosperm cavity into the modified aleurone, aleurone and then to the endosperm is mainly regulated by ZIP and YSL transporters. Zn complexation with phytic acid in the aleurone limits Zn mobility into the endosperm. These insights, together with synchrotron-X-ray-fluorescence microscopy, support the hypothesis that a focus on the mechanisms of Zn loading into the grain will provide new opportunities for Zn biofortification of wheat.

Physio-biochemical and molecular assessment of Iron (Fe2+) toxicity responses in contrasting indigenous aromatic Joha rice cultivars of Assam, India

Iron (Fe) toxicity is one of the major abiotic stresses which limits the yield of lowland rice. This study aims to investigate the physiological, biochemical, and molecular aspects of two contrasting aromatic Joha rice, viz., Keteki and Kola Joha of Assam. Oxidative damage caused due to Fe²⁺ toxicity was quantitatively determined. Fe²⁺ toxicity in the growth medium increases the level of ROS and anti-oxidative enzyme activity. Along with the aforementioned damage caused due to Fe²⁺ toxicity, chlorophyll content decreases in both the rice varieties. Detection of Fe³⁺ and Fe²⁺ was also conducted by Perls' Prussian and Turnbull blue method, respectively. In addition, spectrophotometric quantification of Fe²⁺ was determined by 2, 2'-Bipyridyl (Bpy). Above 2.5 mM, Fe²⁺ toxicity was found to be lethal in rice seedlings affecting their total growth and biomass. Gene expression analysis of iron-regulated transporter 1 (OsIRT1), Yellow Stripe-Like 15 (OsYSL15), and ferritin 1 (OsFer1) revealed the differential gene expression over a time period of Fe²⁺ toxicity. Our study suggested that the different parameters which are considered here can be helpful for the better understanding of how aromatic Joha rice performed under Fe²⁺ toxicity which can also help to reveal broader aspects that how gene players are involved in the iron homeostasis mechanism in Joha rice in coming future.

Chelators of iron and their role in plant's iron management

Proper transport of metal and their homeostasis is very crucial for the growth and development of plants. Plants root are the primary organs which comes in contact with the stress and thus few modifications occurs, often determining the nutrient efficiency or sometimes as a stress tolerance mechanism. Plant utilizes two strategies for the uptake of iron viz, strategy I-reduction based and strategy II-chelation based. In this review we attempted for a better understanding of how the chelators acts in the mechanism of iron uptake from soils to plants and how iron is distributed in the plants.

Tolerance of Iron-Deficient and -Toxic Soil Conditions in Rice

Iron (Fe) deficiency and toxicity are the most widely prevalent soil-related micronutrient disorders in rice (Oryza sativa L.). Progress in rice cultivars with improved tolerance has been hampered by a poor understanding of Fe availability in the soil, the transportation mechanism, and associated genetic factors for the tolerance of Fe toxicity soil (FTS) or Fe deficiency soil (FDS) conditions. In the past, through conventional breeding approaches, rice varieties were developed especially suitable for low- and high-pH soils, which indirectly helped the varieties to tolerate FTS and FDS conditions. Rice-Fe interactions in the external environment of soil, internal homeostasis, and transportation have been studied extensively in the past few decades. However, the molecular and physiological mechanisms of Fe uptake and transport need to be characterized in response to the tolerance of morpho-physiological traits under Fe-toxic and -deficient soil conditions, and these traits need to be well integrated into breeding programs. A deeper understanding of the several factors that influence Fe absorption, uptake, and transport from soil to root and above-ground organs under FDS and FTS is needed to develop tolerant rice cultivars with improved grain yield. Therefore, the objective of this review paper is to congregate the different phenotypic screening methodologies for prospecting tolerant rice varieties and their responsible genetic traits, and Fe homeostasis related to all the known quantitative trait loci (QTLs), genes, and transporters, which could offer enormous information to rice breeders and biotechnologists to develop rice cultivars tolerant of Fe toxicity or deficiency. The mechanism of Fe regulation and transport from soil to grain needs to be understood in a systematic manner along with the cascade of metabolomics steps that are involved in the development of rice varieties tolerant of FTS and FDS. Therefore, the integration of breeding with advanced genome sequencing and omics technologies allows for the fine-tuning of tolerant genotypes on the basis of molecular genetics, and the further identification of novel genes and transporters that are related to Fe regulation from FTS and FDS conditions is incredibly important to achieve further success in this aspect.