The diverse roles of FRO family metalloreductases in iron and copper homeostasis

Abstract

Iron and copper are essential for plants and are important for the function of a number of protein complexes involved in photosynthesis and respiration. As the molecular mechanisms that control uptake, trafficking and storage of these nutrients emerge, the importance of metalloreductase-catalyzed reactions in iron and copper metabolism has become clear. This review focuses on the ferric reductase oxidase (FRO) family of metalloreductases in plants and highlights new insights into the roles of FRO family members in metal homeostasis. Arabidopsis FRO2 was first identified as the ferric chelate reductase that reduces ferric iron-chelates at the root surface-rhizosphere interface. The resulting ferrous iron is subsequently transported across the plasma membrane of root epidermal cells by the ferrous iron transporter, IRT1. Recent work has shown that two other members of the FRO family (FRO4 and FRO5) function redundantly to reduce copper to facilitate its uptake from the soil. In addition, FROs appear to play important roles in subcellular compartmentalization of iron as FRO7 is known to contribute to delivery of iron to chloroplasts while mitochondrial family members FRO3 and FRO8 are hypothesized to influence mitochondrial metal ion homeostasis. Finally, recent studies have underscored the importance of plasma membrane-localized ferric reductase activity in leaves for photosynthetic efficiency. Taken together, these studies highlight a number of diverse roles for FROs in both iron and copper metabolism in plants.

Diversification of Root Hair Development Genes in Vascular Plants

“…For instance, the family containing the Arabidopsis FERRIC REDUCTION OXIDASE4 (FRO4) and FRO5 genes include root-expressed genes from all vascular plant species tested except rice and maize. This implies the loss of this root hair-related gene activity during monocot evolution, perhaps associated with distinct strategies used by grasses for iron acquisition (Jain et al, 2014).…”

Transcriptomes of eight Arabidopsis thaliana accessions reveal core conserved, genotype- and organ-specific responses to flooding stress

“…For instance, FERRIC REDUCTION OXIDASE4 (FRO4) and FRO5 (AT5G23980 and AT5G23990), which play important roles in the uptake of iron and copper from the soil (Bernal et al, 2012;Jain et al, 2014), were identified. Additionally, a vacuolar iron transporter and a metal transporter (VACUOLAR IRON TRANSPORTER-LIKE5 [AT3G25190] and ZRT/ IRT-LIKE PROTEIN2 [AT5G59520]) were classified as potential tolerance genes.…”

Arabidopsis Pollen Fertility Requires the Transcription Factors CITF1 and SPL7 That Regulate Copper Delivery to Anthers and Jasmonic Acid Synthesis

“…Both transcription factors (TFs) regulate gene expression during Cu deficiency through binding to Cu deficiency-responsive elements (59-GTAC-39) in promoters of their targets (Sommer et al, 2010;Yamasaki et al, 2009;Quinn et al, 2000;Birkenbihl et al, 2005;Garcia-Molina et al, 2014;Kropat et al, 2005). Recent transcriptome analyses revealed that SPL7 is required for the expression of the iron (Fe)/Cu reductase oxidases, FRO4 and FRO5, and several Cu transporters, including members of the copper transporter family, COPT1 and COPT2, that together constitute the high-affinity Cu uptake system (Bernal et al, 2012;Gayomba et al, 2013;Jung et al, 2012;Yamasaki et al, 2009;Jain et al, 2014). Among other SPL7-regulated genes are COPT6, members of the yellow stripe-like transporter family, YSL2 and YSL3, and the Cu chaperone CCH, which together contribute to Cu transport to photosynthetic tissues and Cu remobilization from sources to sinks upon senescence (Bernal et al, 2012;Gayomba et al, 2013;Jung et al, 2012;Yamasaki et al, 2009;Chu et al, 2010;Himelblau et al, 1998;Mira et al, 2001;Himelblau and Amasino, 2001).…”