Arabidopsis Copper Transport Protein COPT2 Participates in the Cross Talk between Iron Deficiency Responses and Low-Phosphate Signaling    

Abstract

Copper and iron are essential micronutrients for most living organisms because they participate as cofactors in biological processes, including respiration, photosynthesis, and oxidative stress protection. In many eukaryotic organisms, including yeast (Saccharomyces cerevisiae) and mammals, copper and iron homeostases are highly interconnected; yet, such interdependence is not well established in higher plants. Here, we propose that COPT2, a high-affinity copper transport protein, functions under copper and iron deficiencies in Arabidopsis (Arabidopsis thaliana). COPT2 is a plasma membrane protein that functions in copper acquisition and distribution. Characterization of the COPT2 expression pattern indicates a synergic response to copper and iron limitation in roots. We characterized a knockout of COPT2, copt2-1, that leads to increased resistance to simultaneous copper and iron deficiencies, measured as reduced leaf chlorosis and improved maintenance of the photosynthetic apparatus. We propose that COPT2 could play a dual role under iron deficiency. First, COPT2 participates in the attenuation of copper deficiency responses driven by iron limitation, possibly to minimize further iron consumption. Second, global expression analyses of copt2-1 versus wild-type Arabidopsis plants indicate that low-phosphate responses increase in the mutant. These results open up new biotechnological approaches to fight iron deficiency in crops.

Similarities and Differences in the Acquisition of Fe and P by Dicot Plants

“…In addition, there are numerous works that show similarities between Fe and P deficiency responses, both in the type of responses and in their regulation and signaling. As several works have shown, a consequence of this relationship is the existence of induction of P deficiency responses by Fe deficiency and vice versa [2,4,[54][55][56]103]. This is logical if one considers that there are hormones, such as ethylene, involved in the activation of responses to both deficiencies.…”

“…In previous works, it has been found that Fe deficiency induces the expression of P-related genes, that P deficiency induces the expression of Fe-related genes, and that both deficiencies induce the expression of ethylene-related genes [2,4,[54][55][56][57]. In addition, increased accumulation of Fe in leaves under P deficiency and of P under Fe deficiency has been found [14,37,56,[58][59][60][61][62].…”

Daily rhythmicity of high affinity copper transport

“…Furthermore, analysis of the COPT1, COPT2 and COPT6 promoter regions reveals multiple putative light and circadian cis-regulatory elements. 9,17,18 Some of these motifs are involved in phytochrome regulation of gene expression, 19 which corroborates the reduction of COPT2 transcript in the phy mutants. 15 Such cis-responsive elements could also participate in the regulation of the transcriptional factor SPL7, as they are found in its promoter (Fig.…”

“…8 Among them, COPT2 is the most highly expressed in young and adult tissues. 9 Cu uptake depends on both its availability in the apoplast and the density of Cu transporter proteins at the plasma membrane. 10 Under deficiency, the predominant strategy for Cu acquisition consists in a mechanism of reduction of Cu 2C to Cu C and subsequent Cu C uptake.…”

Function and Regulation of the Plant COPT Family of High-Affinity Copper Transport Proteins

“…This outlook paper focuses on our contribution to characterizing the function and regulation of the different members of the conserved CTR/COPT family of high-affinity Cu transporters in the model plant Arabidopsis thaliana. [6,12,13,[46][47][48]. We observed that, with the exception of COPT4, the ectopic expression of all the Arabidopsis COPT family members expressed in yeast Cu transport mutants stimulates Cu uptake and accumulation [12,13,49].…”