Abstract
Iron is essential for both plant growth and human health and nutrition. Knowledge of the signaling mechanisms that communicate iron demand from shoots to roots to regulate iron uptake as well as the transport systems mediating iron partitioning into edible plant tissues is critical for the development of crop biofortification strategies. Here, we report that OPT3, previously classified as an oligopeptide transporter, is a plasma membrane transporter capable of transporting transition ions in vitro. Studies in Arabidopsis thaliana show that OPT3 loads iron into the phloem, facilitates iron recirculation from the xylem to the phloem, and regulates both shoot-to-root iron signaling and iron redistribution from mature to developing tissues. We also uncovered an aspect of crosstalk between iron homeostasis and cadmium partitioning that is mediated by OPT3. Together, these discoveries provide promising avenues for targeted strategies directed at increasing iron while decreasing cadmium density in the edible portions of crops and improving agricultural productivity in iron deficient soils.
Highlights
Iron (Fe) is essential for plant growth and development and is an important component of the human diet
green fluorescent protein (GFP)-mediated fluorescence was present in the cytosol and did not overlap with chlorophyll autofluorescence in protoplasts transfected with GFP only (Figure 1)
OPT3 belongs to the oligopeptide transporter family, whose members transport synthetic tetra- and pentapeptides when expressed in heterologous systems; the physiological substrates and the physiological role of Oligopetide Transporters (OPTs), including OPT3, in Arabidopsis are unknown (Lubkowitz, 2011)
Summary
Iron (Fe) is essential for plant growth and development and is an important component of the human diet. Cadmium (Cd), on the other hand, is a nonessential and highly toxic element that competes with Fe for uptake and partitioning in plant tissues, posing a threat to crop productivity and human health. The ability of Fe to change its oxidation state (Fe3+ ↔ Fe2+) highlights its importance in biological processes that involve electron transfer reactions (e.g., respiration and photosynthesis). The same property imposes toxicity when Fe is accumulated in cells in excess due to its ability to promote the formation of reactive oxygen species (Valko et al, 2005). Bioavailability of Fe in aerobic soils with neutral to basic pH is below the limits required to sustain plant growth and development because insoluble Fe(III) chelates prevail under these conditions. Alkaline soils, occupying ;30% of the world’s arable
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