Plant iron nutrition in the long road from soil to seeds

Iron (Fe) is an essential plant micronutrient since photosynthesis, respiration, the scavenging of reactive oxygen species and many other cellular processes depend on adequate Fe levels. Nonetheless, non-complexed Fe ions can be dangerous for cells, as they can act as a pro-oxidant. Therefore, plants possess a complex homeostatic control system for safely taking up Fe from the soil, transporting it to the various cellular destinations and for its subcellular compartmentalization. At the end of the plant’s life cycle, maturing seeds are loaded with the required amount of Fe for germination and early seedling establishment. In this review, we discuss recent findings on how the microbiota in the rhizosphere influence and interact with the strategies adopted by plants to take up iron from the soil. We also focus on the process of seed loading with Fe and take into account the Fe metabolism in wild crops’ relatives. These aspects of plant Fe nutrition can represent promising avenues for a better comprehension of the long road of Fe from soil to seeds.

Importance of the Rhizosphere Microbiota in Iron Biofortification of Plants

Increasing the iron content of plant products and iron assimilability represents a major issue for human nutrition and health. This is also a major challenge because iron is not readily available for plants in most cultivated soils despite its abundance in the Earth’s crust. Iron biofortification is defined as the enhancement of the iron content in edible parts of plants. This biofortification aims to reach the objectives defined by world organizations for human nutrition and health while being environment friendly. A series of options has been proposed to enhance plant iron uptake and fight against hidden hunger, but they all show limitations. The present review addresses the potential of soil microorganisms to promote plant iron nutrition. Increasing knowledge on the plant microbiota and plant-microbe interactions related to the iron dynamics has highlighted a considerable contribution of microorganisms to plant iron uptake and homeostasis. The present overview of the state of the art sheds light on plant iron uptake and homeostasis, and on the contribution of plant-microorganism (plant-microbe and plant-plant-microbe) interactions to plant nutritition. It highlights the effects of microorganisms on the plant iron status and on the co-occurring mechanisms, and shows how this knowledge may be valued through genetic and agronomic approaches. We propose a change of paradigm based on a more holistic approach gathering plant and microbial traits mediating iron uptake. Then, we present the possible applications in plant breeding, based on plant traits mediating plant-microbe interactions involved in plant iron uptake and physiology.

Inflammatory Mechanisms in the Pathophysiology of Diabetic Peripheral Neuropathy (DN)—New Aspects

The pathogenesis of diabetic neuropathy is complex, and various pathogenic pathways have been proposed. A better understanding of the pathophysiology is warranted for developing novel therapeutic strategies. Here, we summarize recent evidence from experiments using animal models of type 1 and type 2 diabetes showing that low-grade intraneural inflammation is a facet of diabetic neuropathy. Our experimental data suggest that these mild inflammatory processes are a likely common terminal pathway in diabetic neuropathy associated with the degeneration of intraepidermal nerve fibers. In contrast to earlier reports claiming toxic effects of high-iron content, we found the opposite, i.e., nutritional iron deficiency caused low-grade inflammation and fiber degeneration while in normal or high non-heme iron nutrition no or only extremely mild inflammatory signs were identified in nerve tissue. Obesity and dyslipidemia also appear to trigger mild inflammation of peripheral nerves, associated with neuropathy even in the absence of overt diabetes mellitus. Our finding may be the experimental analog of recent observations identifying systemic proinflammatory activity in human sensorimotor diabetic neuropathy. In a rat model of type 1 diabetes, a mild neuropathy with inflammatory components could be induced by insulin treatment causing an abrupt reduction in HbA1c. This is in line with observations in patients with severe diabetes developing a small fiber neuropathy upon treatment-induced rapid HbA1c reduction. If the inflammatory pathogenesis could be further substantiated by data from human tissues and intervention studies, anti-inflammatory compounds with different modes of action may become candidates for the treatment or prevention of diabetic neuropathy.

Pseudomonas palmensis sp. nov., a Novel Bacterium Isolated From Nicotiana glauca Microbiome: Draft Genome Analysis and Biological Potential for Agriculture

A novel Pseudomonas, designated strain BBB001T, an aerobic, rod-shaped bacterium, was isolated from the rhizosphere of Nicotiana glauca in Las Palmas Gran Canaria, Spain. Genomic analysis revealed that it could not be assigned to any known species of Pseudomonas, so the name Pseudomonas palmensis sp. nov. was proposed. A 16S rRNA gene phylogenetic analysis suggested affiliation to the Pseudomonas brassicae group, being P. brassicae MAFF212427 T the closest related type strain. Upon genomic comparisons of both strains, all values were below thresholds established for differentiation: average nucleotide identity (ANI, 88.29%), average amino acid identity (AAI, 84.53%), digital DNA-DNA hybridization (dDDH, 35.4%), and TETRA values (0.98). When comparing complete genomes, a total of 96 genes present exclusively in BBB001T were identified, 80 of which appear associated with specific subsystems. Phenotypic analysis has shown its ability to assimilate glucose, potassium gluconate, capric acid malate, trisodium citrate, and phenylacetic acid; it was oxidase positive. It is able to produce auxins and siderophores in vitro; its metabolic profile based on BIOLOG Eco has shown a high catabolic capacity. The major fatty acids accounting for 81.17% of the total fatty acids were as follows: C16:0 (33.29%), summed feature 3 (22.80%) comprising C16:1 ω7c and C16:1 ω6c, summed feature 8 (13.66%) comprising C18:1 ω7c, and C18:1ω6c and C17:0 cyclo (11.42%). The ability of this strain to improve plant fitness was tested on tomato and olive trees, demonstrating a great potential for agriculture as it is able to trigger herbaceous and woody species. First, it was able to improve iron nutrition and growth on iron-starved tomatoes, demonstrating its nutrient mobilization capacity; this effect is related to its unique genes related to iron metabolism. Second, it increased olive and oil yield up to 30% on intensive olive orchards under water-limiting conditions, demonstrating its capacity to improve adaptation to adverse conditions. Results from genomic analysis together with differences in phenotypic features and chemotaxonomic analysis support the proposal of strain BBB001T (=LMG 31775T = NCTC 14418T) as the type strain of a novel species for which the name P. palmensis sp. nov is proposed.

Supraoptimal Iron Nutrition of Brassica napus Plants Suppresses the Iron Uptake of Chloroplasts by Down-Regulating Chloroplast Ferric Chelate Reductase

Iron (Fe) is an essential micronutrient for plants. Due to the requirement for Fe of the photosynthetic apparatus, the majority of shoot Fe content is localised in the chloroplasts of mesophyll cells. The reduction-based mechanism has prime importance in the Fe uptake of chloroplasts operated by Ferric Reductase Oxidase 7 (FRO7) in the inner chloroplast envelope membrane. Orthologue of Arabidopsis thaliana FRO7 was identified in the Brassica napus genome. GFP-tagged construct of BnFRO7 showed integration to the chloroplast. The time-scale expression pattern of BnFRO7 was studied under three different conditions: deficient, optimal, and supraoptimal Fe nutrition in both leaves developed before and during the treatments. Although Fe deficiency has not increased BnFRO7 expression, the slight overload in the Fe nutrition of the plants induced significant alterations in both the pattern and extent of its expression leading to the transcript level suppression. The Fe uptake of isolated chloroplasts decreased under both Fe deficiency and supraoptimal Fe nutrition. Since the enzymatic characteristics of the ferric chelate reductase (FCR) activity of purified chloroplast inner envelope membranes showed a significant loss for the substrate affinity with an unchanged saturation rate, protein level regulation mechanisms are suggested to be also involved in the suppression of the reduction-based Fe uptake of chloroplasts together with the saturation of the requirement for Fe.

Social support, nutrition and health among women in rural Bangladesh: complex tradeoffs in allocare, kin proximity and support network size

Malnutrition among women of reproductive age is a significant public health concern in low- and middle-income countries. Of particular concern are undernutrition from underweight and iron deficiency, along with overweight and obesity, all of which have negative health consequences for mothers and children. Accumulating evidence suggests that risk for poor nutritional outcomes may be mitigated by social support, yet how social support is measured varies tremendously and its effects likely vary by age, kinship and reproductive status. We examine the effects of different measures of social support on weight and iron nutrition among 677 randomly sampled women from rural Bangladesh. While we find that total support network size mitigates risk for underweight, other results point to a potential tradeoff in the effects of kin proximity, with nearby adult children associated with both lower risk for underweight and obesity and higher risk for iron deficiency and anaemia. Social support from kin may then enhance energy balance but not diet quality. Results also suggest that a woman's network of caregivers might reflect their greater need for help, as those who received more help with childcare and housework had worse iron nutrition. Overall, although some findings support the hypothesis that social support can be protective, others emphasize that social relationships often have neutral or negative effects, illustrating the kinds of tradeoffs expected from an evolutionary perspective. The complexities of these effects deserve attention in future work, particularly within public health, where what is defined as ‘social support' is often assumed to be positive. This article is part of the theme issue ‘Multidisciplinary perspectives on social support and maternal–child health'.

Root-to-shoot iron partitioning in Arabidopsis requires IRON-REGULATED TRANSPORTER1 (IRT1)

ABSTRACTIRON-REGULATED TRANSPORTER1 (IRT1) is the root high-affinity ferrous iron uptake system and indispensable for the completion of the life cycle of Arabidopsis thaliana without vigorous iron (Fe) supplementation. Here we provide evidence supporting a second role of IRT1 in root-to-shoot mobilization of Fe. We show that the irt1-2 (pam42) mutant over-accumulates Fe in roots, most prominently in the cortex of the differentiation zone, when compared to the wild type. Shoots of irt1-2 are severely Fe-deficient according to Fe content and marker transcripts, as expected. We generated irt1-2 lines producing IRT1 mutant variants carrying single amino-acid substitutions of key residues in transmembrane helices IV and V, Ser206 and His232, which are required for transport activity in yeast. In the transgenic Arabidopsis lines, short-term root Fe uptake rates and secondary substrate Mn accumulation resemble those of irt1-2, suggesting that these plants remain incapable of IRT1-mediated root Fe uptake. Yet, IRT1S206A partially complements rosette dwarfing and leaf chlorosis, as well as root-to-shoot Fe partitioning and gene expression defects of irt1-2, all of which are fully complemented by wild-type IRT1. Taken together, these results suggest a function for IRT1 in root-to-shoot Fe partitioning that does not require Fe transport activity of IRT1. Among the genes of which transcript levels are partially dependent on IRT1, we identify MYB DOMAIN PROTEIN10, MYB DOMAIN PROTEIN72 and NICOTIANAMINE SYNTHASE4 as candidates for effecting IRT1-dependent Fe mobilization in roots. Understanding the biological functions of IRT1 will help to improve iron nutrition and the nutritional quality of agricultural crops.