About this Research Topic
Iron (Fe) is an essential element for all living organisms because it is a cofactor for fundamental biochemical activities such as energy metabolism, oxygen transport and DNA synthesis. Hence both a deficiency and an excess of this transition metal has a strong impact on plant growth. As a consequence, plants must tightly regulate Fe homeostasis and metabolism to allow an effective Fe acquisition, distribution and utilization in the cell in both roots and leaves.
Mitochondria and chloroplasts represent the plant cellular compartments in which Fe is the most requested micronutrient. Indeed, several proteins involved in their Fe uptake mechanism are located in the inner membrane of both mitochondria and chloroplasts. As well, several enzymes belonging both to the respiratory chain and to the TCA cycle are Fe-containing proteins: complex I (NADH:ubiquinone oxidoreductase, Fe/S), complex II (succinate:ubiquinone oxidoreductase, Fe/S and heme), complex III (ubiquinol–cytochrome c oxidoreductase or bc1 complex, Fe/S and heme) and complex IV (cytochrome c oxidase, heme) as well as cytochrome c (heme), AOX (alternative oxidase, di-iron), aconitase (Fe/S), biotin synthase (Fe/S) and ferredoxins (Fe/S). Moreover, important proteins of Fe homeostasis such as frataxin as well as crucial steps of the Fe-S cluster assembly for the entire cell take place in the mitochondrion. Similarly, in the chloroplast is located up to 80% of the cellular iron in leaves. In the photosynthetic apparatus Fe is an essential component of photosystem II (PSII) (iron), PSI (Fe/S, iron), cytochrome b6f (Fe/S and heme) and ferredoxins (Fdx, Fe/S) as well as of enzymes catalyzing chlorophyll synthesis. Similar to mitochondria, Fe is required in chloroplasts for heme and Fe/S cluster synthesis and it is stored in ferritin.
An impaired Fe content in plants induces Fe homeostasis-controlling mechanisms and a complex reprogramming of cellular metabolism, as mitochondria and chloroplasts are the site of essential pathways for plant growth. Indeed, under Fe deficiency, the defective respiratory and photosynthetic pathways lead to remarkable changes in carbon metabolism, including the activation of glycolysis, accumulation of organic acids and induction of several pathways involved in the synthesis of organic Fe-chelating compounds, useful to improve Fe uptake and transport within the plant.
Other than mitochondria and chloroplasts, also vacuoles play a key role in the intracellular compartmentalization of Fe. Sequestration and storage of Fe in vacuole and its remobilization (efflux) are important for plant to maintain cytosolic Fe homeostasis. Numerous ion transporters are located in the tonoplast, as well as organic acid transporters and proton pumps. Since vacuole transporters are involved in ion, organic acid and proton exchange between cytosol and lumen, the vacuole exerts an important role both in Fe homeostasis and in the metabolic changes induced by different Fe availability in plants.
The Research Topic will provide an overview on the new insights of both the Fe homeostasis processes and the metabolism reprogramming occurring in mitochondria, chloroplasts and vacuoles under different Fe nutritional status of plants (both deficiency and excess). We warmly welcome all types of articles, such as original research articles, methods articles, reviews, mini-reviews or perspective articles.
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