Abstract
Numerous central biological processes depend on the participation of the essential elements iron (Fe) or copper (Cu), including photosynthesis, respiration, cell wall remodeling and oxidative stress protection. Yet, both Fe and Cu metal cations can become toxic when accumulated in excess. Because of the potent ligand-binding and redox chemistries of these metals, there is a need for the tight and combined homeostatic control of their uptake and distribution. Several known examples pinpoint an inter-dependence of Fe and Cu homeostasis in eukaryotes, mostly in green algae, yeast and mammals, but this is less well understood in multicellular plants to date. In Arabidopsis, Cu deficiency causes secondary Fe deficiency, and this is associated with reduced in vitro ferroxidase activity and decreased root-to-shoot Fe translocation. Here we summarize the current knowledge of the cross-talk between Cu and Fe homeostasis and present a partial characterization of LACCASE12 (LAC12) that encodes a member of the multicopper oxidase (MCO) protein family in Arabidopsis. LAC12 transcript levels increase under Fe deficiency. The phenotypic characterization of two mutants carrying T-DNA insertions suggests a role of LAC12 in root-to-shoot Fe partitioning and in maintaining growth on Fe-deficient substrates. A molecular understanding of the complex interactions between Fe and Cu will be important for combating Fe deficiency in crops and for advancing biofortification approaches.
Highlights
Copper (Cu) and iron (Fe) are essential micronutrients for plants and most other forms of life
We conducted an in silico analysis to identify candidate MULTICOPPER OXIDASES (MCOs) functioning as ferroxidases based on the best studied MCO FET3 of the high-affinity Fe uptake system of Saccharomyces cerevisiae (Askwith et al, 1994)
In LOW PHOSPATE ROOT 1 (LPR1) and LOW PHOSPATE ROOT 2 (LPR2), two MCOs that act as ferroxidases mediating root phosphate deficiency responses in Arabidopsis, the acidic residues of FET3 are conserved (E269, D370 and D462 in LPR1 and E271, D372 and D464 in LPR2) as shown the structural superimpositions of LPR1 and LPR2 onto FET3, respectively (Müller et al, 2015)
Summary
Copper (Cu) and iron (Fe) are essential micronutrients for plants and most other forms of life. Both elements function as cofactors of important enzymes in a large number of biochemical pathways due to their redox chemical properties, as for example the electron transport chains involved in photosynthesis and mitochondrial respiration (Nouet et al, 2011; Ravet and Pilon, 2013). Cu is required in ethylene perception, cell wall metabolism and oxidative stress responses (Printz et al, 2016). The importance of both micronutrients is even more evident through the deleterious effects that their corresponding deficiencies provoke in plants.
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