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Abstract
The present work describes the effects on iron homeostasis when copper transport was deregulated in Arabidopsis thaliana by overexpressing high affinity copper transporters COPT1 and COPT3 (COPTOE). A genome-wide analysis conducted on COPT1OE plants, highlighted that iron homeostasis gene expression was affected under both copper deficiency and excess. Among the altered genes were those encoding the iron uptake machinery and their transcriptional regulators. Subsequently, COPTOE seedlings contained less iron and were more sensitive than controls to iron deficiency. The deregulation of copper (I) uptake hindered the transcriptional activation of the subgroup Ib of basic helix-loop-helix (bHLH-Ib) factors under copper deficiency. Oppositely, copper excess inhibited the expression of the master regulator FIT but activated bHLH-Ib expression in COPTOE plants, in both cases leading to the lack of an adequate iron uptake response. As copper increased in the media, iron (III) was accumulated in roots, and the ratio iron (III)/iron (II) was increased in COPTOE plants. Thus, iron (III) overloading in COPTOE roots inhibited local iron deficiency responses, aimed to metal uptake from soil, leading to a general lower iron content in the COPTOE seedlings. These results emphasized the importance of appropriate spatiotemporal copper uptake for iron homeostasis under non-optimal copper supply. The understanding of the role of copper uptake in iron metabolism could be applied for increasing crops resistance to iron deficiency.
Highlights
Copper (Cu) and iron (Fe) are transition metals with redox properties that form coordination complexes with organic molecules, acting as essential cofactors in numerous proteins, including components of the respiratory and photosynthetic electron transport chains (Puig et al, 2007; Nouet et al, 2011; Yruela, 2013)
To identify at a molecular level the global effects caused by the deregulation of Cu homeostasis in Arabidopsis, we performed a comparative transcriptomic analysis of 7-day-old wild-type (WT) and a previously generated COPT1 overexpressing (COPT1OE) line (Andrés-Colás et al, 2010), grown under Cu deficiency (1⁄2 MS) and mild Cu excess (1⁄2 MS + 10 Cu) conditions
The induction of COPT1 expression under Cu deficiency in the WT was corroborated by Real-time quantitative PCR (RT-qPCR), as well as its overexpression in COPT1OE seedlings, both under deficiency and excess Cu conditions, in the samples that were used in the hybridizations of the DNA microarrays
Summary
Copper (Cu) and iron (Fe) are transition metals with redox properties that form coordination complexes with organic molecules, acting as essential cofactors in numerous proteins, including components of the respiratory and photosynthetic electron transport chains (Puig et al, 2007; Nouet et al, 2011; Yruela, 2013). These redox properties make Cu and Fe potentially. Metalloprotein substitution contributes to the increase of Fe content under Cu deficiency and vice versa (Waters et al, 2012)
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