A quick journey into the diversity of iron uptake strategies in photosynthetic organisms

Abstract

Iron (Fe) is involved in multiple processes that contribute to the maintenance of the cellular homeostasis of all living beings. In photosynthetic organisms, Fe is notably required for photosynthesis.Although iron is generally abundant in the environment, it is frequently poorly bioavailable. This review focuses on the molecular strategies that photosynthetic organisms have evolved to optimize iron acquisition, using Arabidopsis thaliana, rice (Oryza sativa), and some unicellular algae as models. Nongraminaceous plants, including Arabidopsis, take up iron from the soil by an acidification-reductiontransport process (strategy I) requiring specific proteins that were recently shown to associate in a dedicated complex. On the other hand, graminaceous plants, such as rice, use the so-called strategy II to acquire iron, which relies on the uptake of Fe 3+ chelated by phytosiderophores that are secreted by the plant into the rhizosphere. However, apart these main strategies, accessory mechanisms contribute to robust iron uptake in both Arabidopsis and rice. Unicellular algae combine reductive and non-reductive mechanisms for iron uptake and present important specificities compared to land plants. Since the majority of the molecular actors required for iron acquisition in algae are not conserved in land plants, questions arise about the evolution of the Fe uptake processes upon land colonization.

The AUX1-AFB1-CNGC14 module establishes longitudinal root surface pH profile

“…It is possible that rather than driving cell elongation, the acidic domain in the maturation zone plays a role in nutrient acquisition and absorption by the root hairs (Martín-Barranco et al . 2021).…”

MCO1 and MCO3, two putative ascorbate oxidases with ferroxidase activity, new candidates for the regulation of apoplastic iron excess in Arabidopsis

“…Most organisms express membrane‐bound Fe 3+ reductases that belong either to the cytochrome b561 family (mammals) or to flavo‐cytochromes (fungi and plants). These ferrireductases are crucial for plant nutrition, to mobilize Fe and generate Fe 2+ that is the substrate of both influx (i.e., IRT1, VIT1) and efflux (i.e., NRAMP3, NRAMP4, and ferroportin) membrane transporters (for a recent review, see Martin‐Barranco et al, 2021). In plants, the Fe 3+ reductases identified so far belong to the FRO family.…”

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

“…The FOX1-FTR1 complex is a high-affinity Fe acquisition system that acquires Fe under very low concentrations. Chlamydomonas also directly captures Fe 2+ available in freshwater through the ZIP transporters CrIRT1 and CrIRT2, and the metal ion transporter CrNRAMP4 (Natural Resistance-Associated Macrophage Protein 4) (Figure 1c) (Allen et al, 2007;Blaby-Haas and Merchant, 2012;Glaesener et al, 2013;Kroh and Pilon, 2020;Martín-Barranco et al, 2021). IRT1 is the first described and most well -known member of the large ZIP family of membrane transporters, identified from an Arabidopsis cDNA capable of complementing the Fe uptake function in yeast mutants (Eide et al, 1996).…”

“…Species of the rice genus (Oryza) can combine Strategy II with direct uptake of Fe 2+ via IRT1, in what is called the Combined Strategy. This is probably an adaptation of roots to flooded areas, where the lower O2 levels causes Fe to be reduced to Fe 2+ (Connorton et al, 2017; Wairich et al, 2019; Martín-Barranco et al, 2021).…”

“…The FOX1–FTR1 complex is a high-affinity Fe acquisition system that acquires Fe under very low concentrations. Chlamydomonas also directly captures Fe 2+ available in freshwater through the ZIP transporters CrIRT1 and CrIRT2, and the metal ion transporter CrNRAMP4 (Natural Resistance-Associated Macrophage Protein 4) (Figure 1c) (Allen et al, 2007; Blaby-Haas and Merchant, 2012; Glaesener et al, 2013; Kroh and Pilon, 2020; Martín-Barranco et al, 2021).…”