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

Abstract

Iron (Fe) is an essential micronutrient for virtually all living beings, being practically irreplaceable because of its unique electrochemical properties that enable or facilitate a series of biochemical processes, including photosynthesis. Although Fe is abundant on Earth, it is generally found in the poorly soluble form Fe3+. Most extant plants have established Fe absorption strategies that involve Fe uptake in the soluble form Fe2+. The model angiosperm Arabidopsis thaliana, for example, captures Fe through a mechanism that lowers the pH through proton pumping to the rhizosphere to increase Fe3+ solubility, which is then reduced by a plasma membrane-bound reductase and transported into the cell by the ZIP family protein IRT1. ZIP proteins are transmembrane transporters of a variety of divalent metals such as Fe2+, Zn2+, Mn2+ and Cd2+. In this work, we investigate the evolution of functional homologs of IRT1/ZIP in the supergroup of photosynthetic eukaryotes Archaeplastida (Viridiplantae + Rhodophyta + Glaucophyta) using a dataset of 41 high-quality genomes of diverse lineages. Our analyses suggest that Fe is acquired through deeply divergent ZIP proteins in land plants and chlorophyte green algae, indicating that Fe2+ uptake by ZIP family proteins evolved at least twice independently during green plant evolution. Sequence and structural analyses indicate that the archetypical IRT proteins from angiosperms likely emerged in streptophyte algae before the origin of land plants and might be an important player in green plant terrestrialization, a process that involved the evolution of Fe acquisition in terrestrial subaerial settings.