Deregulated overexpression of the high affinity Cu transporter COPT1 alters iron homeostasis in Arabidopsis

The present work describes the effects on iron homeostasis when copper transport was deregulated in Arabidopsis thaliana by overexpressing copper transporters (COPTOE). A genome-wide analysis conducted on COPT1OE plants, highlighted that iron homeostasis gene expression was affected, both under copper deficiency and excess. Among the inhibited 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. These results emphasized the importance of appropriate spatiotemporal copper uptake for iron homeostasis under copper deficiency. The deregulation of copper-I uptake difficulted the transcriptional activation of the subgroup Ib of basic helix-loop-helix (bHLH-Ib) factors. Oppositely, copper excess inhibited the expression of the master regulator FIT but activate 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, accounting for a defective iron mobilization to the aerial parts, and this effect was exacerbated in COPTOE plants. Thus, iron-III overloading in roots inhibited local iron deficiency responses, aimed to metal uptake from soil, leading to a general lower iron content in the COPTOE seedlings. The understanding of the role of copper uptake in iron metabolism could be applied for increasing crops resistance to iron deficiency At least three biological replicates of Arabidopsis seedlings were generated for 2 genotypes, Col-0 and COPT1 overexpressor line (COPT1 OE); and 2 growth condictions; first one with a cupper deficient medium (Cu Def, 0 μM CuSO4) and a second one with a cupper excess medium (Cu Exc, 10 μM CuSO4). For each growth condition, COPT1 OE versus Col-0 samples were compared; in each comparasion at least three biological replicates were made, two replicas were labeled with Cy5 for the COPT1 OE and Cy3 for the Col-0 sample, while the other replicas were reversed-labeled.