Identification and functional characterization of the ZmCOPT copper transporter family in maize

<div><p>Copper (Cu) is an essential micronutrient for plant growth and development; Cu homeostasis in plant is maintained by the important functions of Ctr/COPT-type Cu transporters. Although the <i>COPT</i> genes have been identified in <i>Arabidopsis thaliana</i> and rice, little is known about Cu transporters in maize. In this study, three-members of putative maize Cu transporters (ZmCOPT 1, 2 and 3) are identified. <i>ZmCOPT</i> genes have expression in all of the tested tissues, including roots, stems, leaves and flowers (male and female), and their expression levels vary responding to stress due to Cu-deficiency and excess. Functional complementation and overexpression together with Cu uptake measurements in <i>ZmCOPTs</i>-transformed <i>ctr1⊿ctr2⊿</i>mutant strain or the wild type strain of <i>Saccharomyces cerevisiae</i> show that the three ZmCOPT members possess the ability to be Cu transporters. Among these, ZmCOPT1 and ZmCOPT2 have high-affinity while ZmCOPT3 has low-affinity. In addition, ZmCOPT2 tend to specifically transport Cu (I) but no other bivalent metal ions.</p>