title: COPT6 is a plasma membrane transporter that functions in copper homeostasis in Arabidopsis and is a novel target of SQUAMOSA promoter-binding protein-like 7.
abstract: Among the mechanisms controlling copper homeostasis in plants is the regulation of its uptake and tissue partitioning. Here we characterized a newly identified member of the conserved CTR/COPT family of copper transporters in Arabidopsis thaliana, COPT6. We showed that COPT6 resides at the plasma membrane and mediates copper accumulation when expressed in the Saccharomyces cerevisiae copper uptake mutant. Although the primary sequence of COPT6 contains the family conserved domains, including methionine-rich motifs in the extracellular N-terminal domain and a second transmembrane helix (TM2), it is different from the founding family member, S. cerevisiae Ctr1p. This conclusion was based on the finding that although the positionally conserved Met(106) residue in the TM2 of COPT6 is functionally essential, the conserved Met(27) in the N-terminal domain is not. Structure-function studies revealed that the N-terminal domain is dispensable for COPT6 function in copper-replete conditions but is important under copper-limiting conditions. In addition, COPT6 interacts with itself and with its homolog, COPT1, unlike Ctr1p, which interacts only with itself. Analyses of the expression pattern showed that although COPT6 is expressed in different cell types of different plant organs, the bulk of its expression is located in the vasculature. We also show that COPT6 expression is regulated by copper availability that, in part, is controlled by a master regulator of copper homeostasis, SPL7. Finally, studies using the A. thaliana copt6-1 mutant and plants overexpressing COPT6 revealed its essential role during copper limitation and excess.
authors.affiliation: Department of Crop and Soil Sciences, Cornell University, Ithaca, New York 14853, USA.
authors.forename: Ha-il
authors.initials: HI
authors.lastname: Jung
authors.forename: Sheena R
authors.initials: SR
authors.lastname: Gayomba
authors.forename: Michael A
authors.initials: MA
authors.lastname: Rutzke
authors.forename: Eric
authors.initials: E
authors.lastname: Craft
authors.forename: Leon V
authors.initials: LV
authors.lastname: Kochian
authors.forename: Olena K
authors.initials: OK
authors.lastname: Vatamaniuk
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D001692:Biological Transport; D002462:Cell Membrane / Q000378:metabolism*; D000079923:Copper Transporter 1; D004268:DNA-Binding Proteins / Q000235:genetics / Q000502:physiology*; D018506:Gene Expression Regulation, Plant; D005816:Genetic Complementation Test; D006706:Homeostasis; D026901:Membrane Transport Proteins / Q000235:genetics* / Q000378:metabolism / Q000502:physiology*; D018613:Microscopy, Confocal / Q000379:methods; D016297:Mutagenesis, Site-Directed; D030821:Plants, Genetically Modified; D011401:Promoter Regions, Genetic; D000080083:SLC31 Proteins; D014157:Transcription Factors / Q000235:genetics / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; C097086:COPT1 protein, Arabidopsis; C576754:COPT6 protein, Arabidopsis; D000079923:Copper Transporter 1; D004268:DNA-Binding Proteins; D026901:Membrane Transport Proteins; D000080083:SLC31 Proteins; C483288:SPL7 protein, Arabidopsis; D014157:Transcription Factors