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Planta (2014) 240:91–101
DOI 10.1007/s00425-014-2067-5
Original Article
Copper homeostasis in grapevine: functional characterization
of the Vitis vinifera copper transporter 1
Viviana Martins · Elias Bassil · Mohsen Hanana ·
Eduardo Blumwald · Hernâni Gerós Received: 15 February 2014 / Accepted: 13 March 2014 / Published online: 2 April 2014
© Springer-Verlag Berlin Heidelberg 2014
Abstract Main conclusion The Vitis vinifera copper transporter
1 is capable of self-interaction and mediates intracellular copper transport.
Abstract An understanding of copper homeostasis in
grapevine (Vitis vinifera L.) is particularly relevant to viticulture in which copper-based fungicides are intensively
used. In the present study, the Vitis vinifera copper transporter 1 (VvCTr1), belonging to the Ctr family of copper
transporters, was cloned and functionally characterized.
Amino acid sequence analysis showed that VvCTr1 monomers are small peptides composed of 148 amino acids with
3 transmembrane domains and several amino acid residues typical of Ctr transporters. Bimolecular fluorescence
complementation (BiFC) demonstrated that Ctr monomers
Electronic supplementary material The online version of this
article (doi:10.1007/s00425-014-2067-5) contains supplementary
material, which is available to authorized users.
V. Martins · H. Gerós Centro de Investigação e de Tecnologias Agro-Ambientais e
Biológicas (CITAB), Vila Real, Portugal
V. Martins · H. Gerós () Grupo de Investigação em Biologia Vegetal Aplicada e Inovação
Agroalimentar—Agrobioplant, Departamento de Biologia,
Escola Ciências, Universidade do Minho, Campus de Gualtar,
4710‑057 Braga, Portugal
e-mail: [email protected]
E. Bassil · E. Blumwald Department of Plant Sciences, University of California, One
Shields Ave, Davis 95616, USA
M. Hanana Center of Biotechnology of Borj Cédria, BP 901,
2050 Hammam‑Lif, Tunisia
are self-interacting and subcellular localization studies
revealed that VvCTr1 is mobilized via the trans-Golgi network, through the pre-vacuolar compartment and located
to the vacuolar membrane. The heterologous expression of
VvCTr1 in a yeast strain lacking all Ctr transporters fully
rescued the phenotype, while a deficient complementation was observed in a strain lacking only plasma membrane-bound Ctrs. Given the common subcellular localization of VvCTr1 and AtCOPT5 and the highest amino
acid sequence similarity in comparison to the remaining
AtCOPT proteins, Arabidopsis copt5 plants were stably
transformed with VvCTr1. The impairment in root growth
observed in copt5 seedlings in copper-deficient conditions was fully rescued by VvCTr1, further supporting
its involvement in intracellular copper transport. Expression studies in V. vinifera showed that VvCTr1 is mostly
expressed in the root system, but transcripts were also present in leaves and stems. The functional characterization
of VvCTr-mediated copper transport provides the first step
towards understanding the physiological and molecular
responses of grapevines to copper-based fungicides.
Keywords Copper transport · Ctr-like proteins ·
Functional complementation · Metal homeostasis · Vitis ·
VvCTr1
Abbreviations
ACT1Actin 1
BCSBathocuproine disulfonic acid
BiFCBimolecular fluorescence complementation
CCHCopper chaperone
CFPCyan fluorescent protein
CTABCetyltrimethylammonium bromide
Ctr/COPTCopper transporter
GAPDHGlyceraldehyde-3-phosphate dehydrogenase
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GFPGreen fluorescent protein
LBLuria–Bertani medium
pCOPT5Promoter region of Arabidopsis COPT5
PIPPlasma membrane intrinsic protein
PVPPolyvinylpyrrolidone
RAN1Responsive to antagonist 1
RFPRed fluorescent protein
RRGRelative root growth
SC-URASynthetic complete medium without uracil
SNARESyntaxin family of soluble N-ethyl maleimide
sensitive factor adaptor protein receptors
TMDTransmembrane domain
VvCTr
Vitis vinifera copper transporter
YFPYellow fluorescent protein
YPEGYeast extract/peptone/ethanol/glycerol medium
Introduction
The uptake of copper in plant cells is tightly regulated to
ensure its accurate distribution to copper-demanding proteins
while also avoiding the inherent toxicity of this highly reactive element. Copper ions play important roles in a number
of physiological processes associated with cell expansion,
fruit ripening and leaf abscission (Fry et al. 2002), namely
photosynthesis, respiration, antioxidant activity, cell metabolism and hormone perception (Himelblau and Amasino 2000;
Pilon et al. 2006; Cohu and Pilon 2010). Redox cycling
between Cu2+ and Cu+ can catalyze the production of toxic
hydroxyl radicals, with deleterious effects on lipids, proteins,
DNA and other biomolecules (Dučić and Polle 2005).
The compartmentation, chelation and exclusion of
metal ions are performed by a complex network of metal
transport pathways that regulate copper homeostasis in
response to changes in external and internal supply (Dučić
and Polle 2005; Gasic and Korban 2006; Yruela 2009).
Within the plant cell, copper is required in several subcellular compartments: the cytosol, endoplasmic reticulum
(ER), mitochondrial inner membrane, chloroplast stroma
and thylakoid lumen as well as the apoplast. Both the mitochondria and plastids are copper sinks, and the vacuole
sequesters significant amounts of copper and contribute to
copper delivery within the cell (Pilon et al. 2006; Martins
et al. 2012). A copper chaperone (CCH) and a responsive to
antagonist 1 (RAN1) were the first copper delivery systems
identified in plant cells (Himelblau and Amasino 2000).
The latter is a member of The PIB-type family of membrane
transport ATPases (Peñarrubia et al. 2010) which couple
copper transport from the cytosol into secretory compartments or the extracellular space to the hydrolysis of ATP
(Mandal et al. 2004; Pilon et al. 2006).
The initial uptake of copper into plant cells is performed by the family of COPT transporters belonging
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Planta (2014) 240:91–101
to a highly conserved Ctr-like copper transporter family
(Puig and Thiele 2002; Peñarrubia et al. 2010; Yuan et al.
2011). Six genes encoding COPT transporters were identified in Arabidopsis, COPT1-6 (Kampfenkel et al. 1995;
Sancenón et al. 2003; Puig et al. 2007; Jung et al. 2012;
Garcia-Molina et al. 2013; Perea-García et al. 2013) and
a family comprising seven members was identified in rice
(Oryza sativa; Yuan et al. 2011). Whereas all the OsCOPTs
appear to be plasma membrane-bound proteins, the
AtCOPTs are localized in different cellular compartments
including the plasma membrane (COPT1, COPT2, COPT6;
Andrés-Colás et al. 2010; Jung et al. 2012; Perea-García
et al. 2013) where they function in copper uptake, and the
tonoplast (COPT5; Klaumann et al. 2011) where they are
believed to mediate copper export to the cytosol.
Defects in COPT-mediated copper transport induce
changes in copper distribution that affect root elongation,
vegetative growth, chlorophyll content, responses to iron
deficiency and low-phosphate signaling, pollen development, and, ultimately, plant survival (Sancenón et al. 2004;
Andrés-Colás et al. 2010; Garcia-Molina et al. 2011; Klaumann et al. 2011; Jung et al. 2012; Perea-García et al. 2013).
Previously, we identified eight putative CTrs in Vitis
vinifera, but their role in copper transport has not yet
been determined. In the present study, we characterized
the Vitis vinifera Copper Transporter 1 (VvCTr1) and
assessed its subcellular localization. The heterologous
expression of VvCTr1 in yeast ctrΔ strains and in Arabidopsis COPT5 mutants suggested that VvCTr1 functions
as copper transporter and provided insights about its
contribution for copper mobilization within the cell. Following previous studies showing that VvCTr1 expression
is modulated by several stress conditions, including copper excess (Martins et al. 2012), the presence of VvCTr1
transcripts in the roots, stem and leaves of grapevines cv.
“Trincadeira” suggests that it may act as a core regulator of copper homeostasis in grapevine. The characterization of CTr-mediated copper transport is of particular
importance in the viticulture context in which copper is
widely used as the active component of several fungicides
(McCallan 1948; Deacon 2006), raising concerns regarding negative impacts in grapevine physiology and in the
metabolism of grape cells (Fleming and Trevors 1989;
Martins et al. 2012).
Materials and methods
In silico sequence analysis of COPT/Ctr proteins
Alignment of multiple amino acid sequences was performed with Prankster software (http://www.ebi.ac.
uk/goldman-srv/prank/prankster) and analyzed on GeneDoc
Planta (2014) 240:91–101
(http://www.nrbsc.org/gfx/genedoc). Phylogenetic trees
were obtained with Phylip-3.69 software (http://evolution.
genetics.washington.edu/phylip) and analyzed on Mega 4.0
(http://www.megasoftware.net/mega4). Bootstrap values
from 1000 trials were used. Predictions of transmembranespanning domains were performed with PSIPRED Server
(http://bioinf.cs.ucl.ac.uk/psipred).
Plasmid constructs
The complete VvCTr1 coding sequence was amplified via
PCR from grape berry cDNA using gene-specific primers
(Online Resource Fig. S1) flanked by attB sites, and cloned
into the vector pDONR207 through a BP reaction (Invitrogen Gateway® Technology). The resulting entry clone
was used for recombination with plant and yeast expression vectors through LR reactions. In fusions of fluorescent
proteins to the C terminus of VvCTr1, the stop codon was
omitted in the reverse primer.
For subcellular localization studies, the entry clone
carrying VvCTr1 was recombined into pH7FWG2 for
green fluorescent protein (GFP) fusion and pH7RWG2
for red fluorescent protein (RFP) fusion (Karimi et al.
2002). For protein interaction studies through bimolecular fluorescence complementation the entry clone carrying VvCTr1 was recombined into the binary BiFC vectors
pDEST-VYNEGW and pDEST-GWVYNE for N- or C-terminal fusions to VenusN, respectively, and into pDESTSCYCEGW and pDEST- GWSCYCE for N- or C-terminal
fusions to S(CFP)3AC, respectively (Gehl et al. 2009).
For expression of VvCTr1 in yeast cells, the entry clone
was recombined with the destination vector pVV214
containing the strong PGK promoter (Van Mullem et al.
2003). For expression of VvCTr1 in Arabidopsis copt5
plants, the pH7FWG2-VvCTr1 construct was digested
with SacI and SpeI (New England BioLabs®, Inc.) following the manufacturer’s instructions, resulting in the
excision of the CaMV35S promoter. In parallel, the promoter region of AtCOPT5 gene (pCOPT5, from nucleotide −357 to the ATG; Garcia-Molina et al. 2011) was
amplified using primers flanked by the restriction sites of
SacI and SpeI: Fwd 5′-AATGAGCTCACCAGAATCAGG
TTAACAC-3′, Rev 5′-TTACTAGTCTTTGCGAGCTTG
ATTTGAGC-3′). T4 ligase (New England BioLabs®,
Inc.) was used to introduce the amplicon into the digested
pH7FWG2-VvCTr1 plasmid, placing VvCTr1 under the
control of pCOPT5. All constructs were confirmed by
sequencing.
Subcellular localization of VvCTr1
Expression vectors were introduced in Agrobacterium
tumefaciens (GV3101) and transient transformation of
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tobacco leaf epidermal cells was performed based on the
method of Sparkes et al. (2006). Briefly, bacterial cultures were grown overnight on liquid LB medium with
the appropriate antibiotic selection to exponential-stationary phase and then diluted to OD600 nm = 0.08 in
infiltration buffer (50 mM MES pH 5.6, 2 mM Na3PO4,
0.5 % glucose and 100 μM acetosyringone) and grown to
OD600 nm = 0.2. Four-week-old tobacco plants (Nicotiana
benthamiana L.) were infiltrated with the bacterial cultures
and leaf disks were examined under the confocal microscope after 3 days.
To study VvCTr1 subcellular localization, tobacco
plants were co-infiltrated with Agrobacterium strains
carrying one of VvCTr1 plant expression vectors and
constructs of Arabidopsis proteins with well-known cell
locations. The construct wave138Y consisting of the aquaporin PIP1;4 fused to EYFP in pNIGEL backbone was
used to label the plasma membrane. Similarly, wave13Y
consisting of the SNARE VTI12 fused to EYFP was used
to target the trans-Golgi/early endosome compartment
(Geldner et al. 2009). A construct consisting of the coding
sequence of AtCOPT5 fused to RFP in pH7RWG2 plasmid was used to label the vacuole membrane/pre-vacuolar
compartment (Garcia-Molina et al. 2011; Klaumann et al.
2011).
Protein–protein interactions
The association between VvCTr1 monomers was tested
through BiFC in which the N- and C-terminal sub-fragments of the fluorescent protein VenusN/S(CFP)3AC were
fused separately to VvCTr1. Tobacco plants were co-transformed with the constructs of VvCTr1 fused to VenusN
and VvCTr1 fused to S(CFP)3AC by its N or C terminus.
The combination of VvCTr1-S(CFP)3AC and RemorinVenusN was used as negative control and Remorin-VenusN
with Remorin-S(CFP)3AC was used as positive control
for protein–protein interactions (Tajima and Blumwald,
unpublished).
Fluorescence microscopy
Fluorescence microscopy was performed using a Zeiss confocal laser scanning microscope (LSM 710 AxioObserver).
The excitation wavelength was 488 nm for GFP and YFP
and 594 nm for RFP, and emission was 500–535 nm for
GFP, 530–590 nm for YFP and 600–660 nm for RFP. For
multicolor imaging of GFP/RFP and YFP/RFP, sequential
scanning was used to avoid crosstalk between fluorescence
channels. For BiFC studies, the excitation and emission
wavelengths were set at 488 and 515 nm, respectively.
Images were processed with ZEN Lite 2011 software (Carl
Zeiss Microscopy).
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Yeast transformation and growth assays
The lithium acetate procedure was used to transform plasmid DNA into the yeast ctr1Δctr3Δ double-mutant strain
MPY17 (MATα, ctr1::ura3::kanR, ctr3::TRP1, lys2-801,
his3), and the yeast ctr1Δctr3Δctr2Δ triple-mutant strain,
which display a severe or total loss of Ctr high-affinity
copper transport (Peña et al. 1998; Rees et al. 2004). Yeast
cells transformed with the empty vector (pVV214) or with
VvCTr1 were grown in SC-ura (glucose-rich medium) to
OD600 nm = 1.0, washed, and several tenfold diluted clones
were plated as drops on selective media (YPEG: 2 % ethanol, 3 % glycerol-rich medium) with or without supplement
of CuSO4 (0–100 μM). Plates were incubated for 9 days at
30 °C.
Transformation of Arabidopsis copt5 plants and assessment
of relative root growth
The Arabidopsis T-DNA insertion line used in this study
(Online Resource Fig. S2; NASC ID: N593550–copt5-2;
Garcia-Molina et al. 2011) was kindly provided by Dr
Lola Peñarrubia (Departament de Bioquímica y Biología
Molecular, Universitat de València, Spain) and the presence of the T-DNA insertion within the COPT5 locus
was confirmed after genotyping. The copt5 homozygous
line was transformed by floral dipping (Clough and Bent
1998) with the modified pH7FWG2–VvCTr1 construct in
which VvCTr1 was placed under the control of pCOPT5.
The transformed copt5 plants were self-pollinated, and
homozygous lines were obtained. The presence of VvCTr1
in the genome of transformed copt5 lines was confirmed
by PCR (Online Resource Fig. S3). For assessment of the
root phenotype, seeds of homozygous copt5 lines carrying VvCTr1 were initially germinated in ½ Murashige and
Skoog solid medium (10 mM MES, pH 5.7; Murashige
and Skoog 1962), at 20 °C, in a 16-h light/8-h dark photoperiod, together with wild-type Col 0 and untransformed
copt5 lines. Four-day-old seedlings were then transferred to
½ MS medium supplemented with 75 μM BCS (bathocuproine disulfonic acid, Sigma-Aldrich Co. LLC) to create
copper deficiency, and incubated in the same conditions.
The relative root growth (RRG) was evaluated after 8 days.
Grapevine growing conditions
Grapevines (V. vinifera L.) cv. “Trincadeira” were obtained
from the “Instituto Nacional de Investigação Agrária” (Oeiras, Portugal). Plants were grown for 5 months, at 24 °C,
under a 16-h light/8-h dark photoperiod, after subculture of
apical meristems in basal Murashige and Skoog medium
(Murashige and Skoog 1962). The grapevine organs,
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Planta (2014) 240:91–101
namely root, stem and leaves, were carefully separated,
immediately frozen in liquid nitrogen and stored at −80 °C.
Analysis of VvCTr1 expression in grapevine
Frozen samples were ground in liquid nitrogen and total
RNA was extracted in buffer containing 100 mM Tris–
HCl (pH 8), 2 M NaCl, 25 mM EDTA, 2 % CTAB, 2 %
PVP and 2 % β-mercaptoethanol. RNA purification was
performed with the RNeasy® Plant Mini Kit (Qiagen) and
samples were treated with DNAse to remove any contaminating DNA. mRNA was converted to cDNA by reverse
transcription with an Omniscript® RT Kit and oligo(dT)
primers (Qiagen). Quantitative real-time PCR (qPCR) was
performed in 96-well plates with QuantiTect SYBR Green®
Master Mix (Qiagen). For each sample (biological replicate), qPCR reactions were performed in triplicate (technical replicates) using 10 μl Master Mix, 300 nM of each
primer, 1 μl of diluted cDNA and nuclease-free water to a
final volume of 20 μl. The following cycler conditions were
used: 15 min at 95 °C and 45 cycles of 15 s at 95 °C, 30 s at
55 °C and 30 s at 72 °C. Fluorescence was measured at the
end of each amplification cycle. Primers were designed to
specifically anneal with VvCTr1: Fwd 5′-AGGTGGTGGA
GGTGGAGAACT-3′, Rev 5′-ACAGAGCCAATACAA
AGCCA-3′ (Online Resource Fig. S1). Gene expression was
normalized to the V. vinifera glyceraldehyde-3-phosphate
dehydrogenase gene (VvGAPDH; NCBI/GenBank Database
accession no. XM_002263109) and the V. vinifera actin 1
gene (VvACT1, XM_002282480). The following primers
were used: GAPDH_Fwd 5′-CTTTCCGTGTTCCTACTG
TTG-3′, GAPDH_Rev 5′-CCTCTGACTCCTCCTTGAT-3′;
ACT1_Fwd 5′-CTTGCATCCCTCAGCACCTT-3′, ACT1_
Rev 5′-TCCTGTGGACAATGGATGGA-3′. The correctness of all qPCR products obtained was controlled on agarose gels and the specificity of the individual PCR reactions
was checked through dissociation curves at the end of each
qPCR reaction, by heating the amplicons from 65 to 95 °C.
Data were analyzed using the CFX Manager Software (BioRad Laboratories, Inc.).
Statistical analysis
The relative root growth of Arabidopsis copt5 seedlings
was compared to that of VvCTr1 complemented lines by
the Student’s t test using Prism® 5 (GraphPad Software,
Inc.). In graphs, the values are marked with asterisks to
denote the significance level: ***P ≤ 0.001. The expression of VvCTr1 in the different grapevine organs was compared by one-way ANOVA (GraphPad Software, Inc.). In
graphs, significant differences are marked by different letters (a, b).
Planta (2014) 240:91–101
95
Results
VvCTr1 monomers form a multimeric functional complex
In silico characterization of VvCTr1
To assess whether VvCTr1 proteins were able to assemble as multimers, a bimolecular fluorescence complementation (BiFC) technique was performed. We used
the N terminus of the yellow fluorescent protein Venus
(VenusN) and the C terminus of the cyan fluorescent
protein S(CFP)3A (S(CFP)3AC) to assess the formation
of a complex between monomeric forms of VvCTr1.
Each of the fragments by itself displays no fluorescence; however, following the close interaction between
the fusion proteins, VenusN associates with S(CFP)3AC
restoring the fluorescent protein VenusN/S(CFP)3AC
and resulting in a chimerical signal for Venus plus
CFP which is detected at 515 nm (green fluorescence;
Gehl et al. 2009). As shown in Fig. 3, when tobacco
plants were transiently co-transformed with the fusion
proteins VvCTr1-VenusN and VvCTr1- S(CFP)3AC a
strong fluorescent signal was observed indicating that
VvCTr1 monomers had the ability to form homo-multimers. When the fragments of the fluorescent protein
were fused to the N terminus of VvCTr1 (N’ fusion)
the signal was significantly weaker than that observed
in the C-terminal fusion. Moreover, the co-expression
of VvCTr1-S(CFP)3AC and of the membrane-associated protein Remorin tagged to VenusN resulted in no
detectable fluorescence (negative control), confirming
that only the close association between fusion proteins
would allow reassembly of the fluorescent protein, as
in the co-expression of Remorin-VenusN and RemorinS(CFP)3AC (positive control; Tajima and Blumwald,
unpublished).
The amino acid sequence of VvCTr1 was examined in silico and a phylogenetic analysis was performed to study its
evolutionary relationship with other COPT/Ctr proteins
(Fig. 1a). This analysis revealed that VvCTr1 belongs
to a major group of Ctr-like proteins from higher plants
comprised by six COPTs from Arabidopsis thaliana and
seven COPTs from O. sativa, and clusters together with
the AtCOPT5 and the OsCOPT7. Similarly to other Ctrlike proteins, VvCTr1 monomers are small peptides
composed of 148 amino acids, contain 3 transmembrane
domains and MxxxM and GxxxG (x representing any
amino acid) motifs present in TMD2 and TMD3, respectively (Fig. 1b).
Subcellular localization of VvCTr1
To assess the subcellular localization of VvCTr1, tobacco
plants were transiently co-transformed with constructs
where VvCTr1 was fused to GFP or RFP and constructs
of fusion proteins with known cell locations. As shown
in Fig. 2, there was no co-localization between aquaporin
PIP1;4 targeted to the plasma membrane (Boursiac et al.
2005; Geldner et al. 2009) and the signal corresponding
to VvCTr1-RFP. To investigate the possible localization
of VvCTr1 to intracellular membranes, VvCTr1-RFP and
VTI12-YFP were co-expressed. VTI12 belongs to the
family of SNARE proteins which are involved in fusion
of transport vesicles with specific organelles and targeted
the trans-Golgi/early endosome network (Sanderfoot
et al. 2001; Geldner et al. 2009). Similar to VTI12-YFP,
VvCTr1-RFP appeared as small vesicles consistent with
trafficking endosomal bodies (Fig. 2). A partial co-localization was seen between VvCTr1 and VTI12, suggesting
the localization of VvCTr1 to the trans-Golgi/early endosome network. In addition, VvCTr1-GFP and COPT5RFP displayed significant co-localization (Fig. 2). Recent
studies showed a clear localization of COPT5 to prevacuolar vesicles (Garcia-Molina et al. 2011) and to the
vacuole membrane (Klaumann et al. 2011). The partial
localization of VvCTr1 to the early endosomal network
and its clear co-localization to COPT5-RFP suggested
the trafficking of VvCTr1 via the trans-Golgi network,
through the pre-vacuolar compartment and its destination
to the tonoplast. Further confirmation of the localization
of VvCTr1 to the vacuole membrane was achieved after
subjecting the cells to an osmotic shock (Online Resource
Fig. S4).
Functional complementation of yeast Ctr mutants
The potential role of VvCTr1 in copper transport was
initially investigated in S. cerevisiae ctr1Δctr3Δ and
ctr1Δctr3Δctr2Δ strains. While the former lacks only
the Ctrs located to the plasma membrane, the latter also
lacks its vacuolar Ctr, being deprived of all high-affinity
copper transporters. These mutants are characterized
by a defective mitochondrial respiratory chain since
cytochrome c oxidase cannot obtain its copper cofactor
(Peña et al. 1998). Both mutants were transformed with
VvCTr1 and their growth was analyzed in several growth
media. As shown in Fig. 4, both mutants containing the
vector alone were unable to grow in ethanol/glycerol
medium (YPEG) with no supplement of copper (0 μM
CuSO4). Unlike the double mutant, the triple mutant carrying the vector alone could not grow even in the presence of 10 μM CuSO4. However, the presence of VvCTr1
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Planta (2014) 240:91–101
Fig. 1 Primary sequence analysis of VvCTr1 and other members of
the COPT/Ctr family. a Phylogenetic relationship of VvCTr1 (accession number of GenBank or Protein database of National Center for
Biotechnology Information: HQ108185) and other COPT/Ctr proteins from different species: A. thaliana (AtCOPT1, NP_200711;
AtCOPT2, NP_190274; AtCOPT3, NP_200712; AtCOPT4,
NP_850289; AtCOPT5, NP_197565; AtCOPT6, NP_850091), O.
sativa (OsCOPT1, NP_001044379; OsCOPT2, NP_001055594;
OsCOPT3, NP_001044380; OsCOPT4, NP_001173438; OsCOPT5,
NP_GQ387495; OsCOPT6, NP_001173929; OsCOPT7, HQ833657),
S. cerevisiae (ScCtr1, NP_015449; ScCtr2, NP_012045; ScCtr3,
NP_013515), human (hCtr1, NP_001850; hCtr2, NP_001851),
mouse (mCtr1, NP_780299), lizard (PsCtr1, CAD13301), zebrafish
(DrCtr1, NP_991280), fruitfly (DmCtr1A, NP_572336; DmCtr1B,
NP_649790; DmCtr1C, NP_651837), C. gloeosporioides (CgCtr2,
ABR23641) and green algae (CrCtr1, XP_001693726; CrCtr2,
XP_001702470; CrCtr3, XP_001702650). The numbers for interior
branches indicate the bootstrap values (%) for 1000 replications. The
scale at the bottom is in units of number of amino acid substitutions
per site. b Alignment of COPT/Ctr family copper transport proteins.
Conserved features comprise three transmembrane domains (TMD1–
3, shown in red), methionine-rich motifs consisting of 2–5 methionine residues usually separated by three or fewer amino acids (in
blue), Gly motifs arranged as GxxxG (in orange) and Cys/His motifs
composed of three amino acids in which two are cysteines or histidines (in green). The length of each protein in amino acids is shown
on the right
fully restored the growth defect of the triple mutant in
this condition, suggesting its involvement in copper
transport. In contrast, the lack of growth of the double
mutant containing the vector alone in a medium with no
supplement of copper (0 μM CuSO4) was only partially
restored by VvCTr1.
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Planta (2014) 240:91–101
97
Fig. 2 Subcellular localization
of VvCTr1. Tobacco plants were
transiently co-transformed with
Agrobacterium strains carrying
the construct of VvCTr1 fused
to RFP or GFP and constructs
of fusion proteins with known
cell locations: PIP1;4 (plasma
membrane), VTI12 (trans-Golgi
network/early endosome) and
COPT5 (pre-vacuolar compartment/vacuole). Images
were acquired in a confocal
microscope and show green
fluorescence (VvCTr1-GFP),
red fluorescence (VvCTr1RFP, COPT5-RFP), yellow
fluorescence (PIP1;4-YFP,
VTI12-YFP) and the overlap
of fluorescence signals (merge,
zoom in). Bar 30 μm
Fig. 3 Formation of oligomeric complexes by VvCTr1 monomers. A
bimolecular fluorescence complementation technique was performed
in tobacco plants transiently transformed with constructs consisting
of N′ or C′ fusions of VvCTr1 with the N- or C-terminal sub-fragments of Venus and S(CFP)3A, respectively. The tight interaction of
the fusion proteins mediates refolding and reconstitution of the fluorescent protein, resulting in efficient fluorescence emission that was
analyzed under a confocal microscope. A negative control for protein
interaction was performed with VvCTr1 fused to S(CFP)3AC and the
membrane-associated protein Remorin fused to VenusN. The interaction between Remorin-VenusN and Remorin-S(CFP)3AC was used
as positive control. Bar 20 μm. Inset model of the multimer assembly and BiFC between VvCTr1 monomers fused with VenusN or
S(CFP)3AC
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Expression of VvCTr1 in planta
To assess the involvement of VvCTr1 in V. vinifera copper
homeostasis, its expression was studied by real-time PCR
in distinct grapevine organs cv. “Trincadeira”. As shown in
Fig. 6 VvCTr1 transcripts were present in the roots, stem
and leaves. The highest expression was detected in the
roots, followed by the leaves and the stems.
Discussion
Fig. 4 Functional
complementation
of
S.
cerevisiae
ctr1Δctr3Δctr2Δ and ctr1Δctr3Δ strains by VvCTr1. Yeast mutants
were transformed with the vector pVV214 alone (empty vector) or
with the same vector carrying VvCTr1. Cells were grown on glucose (SC-ura) or on ethanol/glycerol (YPEG)-selective media supplemented with 10–100 μM CuSO4 or without supplementation of
CuSO4 (0), for 9 days
Functional complementation in Arabidopsis copt5
seedlings
In addition to the good co-localization of VvCTr1 and
AtCOPT5, the former shares the highest amino acid
sequence similarity with the latter (53 %), in comparison
to the sequences of the remaining Arabidopsis COPT proteins. To confirm the role of VvCTr1 in mediating copper
transport in a plant system, VvCTr1 was stably expressed
in Arabidopsis COPT5 knockout mutants. The mutant
seedlings are characterized by reduced root growth in copper-deficient conditions (Garcia-Molina et al. 2011; Klaumann et al. 2011) and the ability of VvCTr1 to rescue this
phenotype was evaluated. As shown in Fig. 5, the relative
root growth (RRG) of copt5 seedlings was similar to that
observed in wild-type plants and in homozygous copt5
lines transformed with pCOPT5-VvCTr1, in copper-sufficient conditions (½ MS). However, in copper-deficient
conditions (+75 μM BCS), the RRG of copt5 seedlings
was impaired, decreasing by 35 % in comparison to wildtype plants. VvCTr1 successfully rescued the root phenotype of copt5 seedlings, where a full recovery of RRG was
observed.
13
The characterization of copper transport pathways in grapevines holds important basic and applied relevance due to
the intensive use of copper-based fungicides, mainly in
organic viticulture (Deacon 2006; García-Esparza et al.
2006). In silico analysis revealed that, like other COPT/Ctr
proteins, VvCTr1 contains three transmembrane domains
(TMDs), an N terminus rich in methionine motifs and a C
terminus containing two cysteine residues. Extensive studies performed in the human Ctr1 and yeast Ctrs contributed
to elucidate the role of these key residues in the assembly
and function of Ctr transporters (Aller et al. 2004; Eisses
and Kaplan 2005; Aller and Unger 2006; De Feo et al.
2010). TMD1 appears to participate in molecular interactions of Ctrs with ferric reductases that reduce Cu2+ to Cu+
(Rees and Thiele 2007), while TMD2 contains the highly
conserved motif MxxxM that seems to be the key for regulation of the size of the pore and is required for Ctr function (De Feo et al. 2010; Peñarrubia et al. 2010; Jung et al.
2012). TMD3 contains the highly conserved GxxxG motif
that appears to be responsible for the close packing of the
three TMDs, being critical for forming a functional and
structurally mature transporter (Aller et al. 2004; De Feo
et al. 2009; Peñarrubia et al. 2010). The methionine motifs
present in the N terminus of most Ctrs are important in
copper binding for facilitated import, especially in copperlimiting conditions (Jung et al. 2012), while the cysteines
present in the C-terminal cytosolic domain seem to contribute to oligomerization and stability of the protein and serve
as intracellular copper donors for its mobilization to copper
chaperones (Eisses and Kaplan 2002; Nose et al. 2006).
Bimolecular fluorescence complementation (BiFC)
performed in this study showed that VvCTr1 monomers
interact with each other, forming homodimers or highermolecular-mass oligomers with the potential to assemble as
functional mature copper transporters. These findings are in
support of previous observations that showed that mature
Ctrs may form multimeric complexes capable of creating
a selective pore for copper (De Feo et al. 2009; Peñarrubia et al. 2010). When the fluorescent tags were placed
before the N terminus of VvCTr1, this interaction was significantly weaker than in C-terminal fusions, indicating
Planta (2014) 240:91–101
Fig. 5 Functional complementation of A. thaliana copt5 seedlings by
VvCTr1. copt5 plants was stably transformed with pCOPT5-VvCTr1
and homozygous lines were obtained (see “Materials and methods”).
The relative root growth of wild-type Col 0, copt5, and VvCTr1 complemented independent lines (VvCTr1_1 and VvCTr1_2) was evalu-
Fig. 6 Expression of VvCTr1 in grapevines cv. “Trincadeira” by realtime PCR. Gene expression was normalized to the transcript levels of
ACT1 and GAPDH (internal standards). Results indicate mean ± SD
of values obtained for five biological replicates. In bars, different letters indicate significant differences (P ≤ 0.001)
that the N terminus of VvCTr1 has a major role in VvCTr1VvCTr1 interactions. Accordingly, yeast two-hybrid studies have shown that the N-terminal portion of human
hCtr1 is capable of self-interaction (Klomp et al. 2003).
It is well established that the hCtr1 forms symmetrical
99
ated in copper-sufficient (½ MS) and in copper-deficient conditions
(½ MS + 75 μM BCS) after 8 days. Results are expressed as percentage of mean ± SD of RRG compared to Col 0; n = 24. Asterisks
denote the significance level as compared to VvCTr1 complemented
lines: ***P ≤ 0.001
homotrimers containing nine transmembrane helices with
a selective pore between the subunit interfaces (Aller and
Unger 2006; De Feo et al. 2009) and this model was initially extrapolated to Ctrs from other eukaryotes, and sometimes validated, as the case of S. cerevisiae Ctr3 (Peña et al.
2000). However, it is now known that the S. cerevisiae
Ctr1 appears to form trimers as well as higher molecular
weight complexes (Sinani et al. 2007). The complexity of
Ctr transport becomes even higher with the possible formation of hetero-oligomeric complexes, as the case of the
Schizosaccharomyces pombe Ctr4 and Ctr5 whose interaction is necessary for the proper localization of each subunit to the plasma membrane and transporter activity (Zhou
and Thiele 2001). In plants such as rice and Arabidopsis
where 7 and 6 COPTs were already identified, respectively, the number of possible combinations is even higher
and the formation of specific homo- and heteromeric complexes between COPTs has been shown (Yuan et al. 2011;
Jung et al. 2012). These studies suggested that the specific
assembly of Ctr proteins could determine their subcellular
localization and affinity for copper.
Complementation assays using Saccharomyces cerevisiae strains defective in copper uptake allowed the characterization of some Ctr-like proteins, including the human
13
100
Ctr1 (Zhou and Gitschier 1997) and several COPTs (Kampfenkel et al. 1995; Sancenón et al. 2003; Yuan et al. 2011;
Jung et al. 2012). In the present study, VvCTr1 fully complemented the growth defect of the yeast ctr1Δctr3Δctr2Δ,
lacking all high-affinity copper transport, validating its
function as a copper transporter. However, the phenotype
complementation by VvCTr1 in yeast ctr1Δctr3Δ, lacking only plasma membrane Ctrs, was only partial, suggesting its localization to internal membranes. In fact, it
has been previously shown that Arabidopsis AtCOPT1 and
AtCOPT2 localized to the plasma membrane fully complemented the growth defect of the yeast double mutant, while
AtCOPT3 and AtCOPT5 that locate to internal membranes
only partially complemented it (Sancenón et al. 2003; Garcia-Molina et al. 2011).
Subcellular localization of VvCTr1 was performed in
tobacco plants co-expressing fusion proteins with wellknown cell locations. Sharing a high amino acid sequence
similarity with AtCOPT5, VvCTr1 co-localized with this
protein, being mobilized through the trans-Golgi network
to the pre-vacuolar compartment/vacuolar membrane
where it could mediate copper release to the cytosol (Klaumann et al. 2011), and also be involved in copper movements through the pre-vacuolar compartment, which could
act in copper recycling through vesicles that provide the
metal cofactor to key copper-dependent processes such as
photosynthesis (Garcia-Molina et al. 2011). Arabidopsis
copt5 lines show defective root growth in copper-limiting
conditions because the route for copper export is blocked
and the metal remains trapped inside the vacuole, preventing long-distance transport (Garcia-Molina et al. 2011;
Klaumann et al. 2011). In the present study, VvCTr1 was
able to complement the root phenotype of copt5 seedlings,
suggesting its essential role in plantlet development under
copper-deficient conditions. The major role of VvCTr1 in
the root system was further supported by expression studies
in grapevines. Being highly expressed in the roots, but also
present in other grapevine organs, including the stem and
leaves, VvCTr1 could have a major role in the regulation of
copper mobilization. The presence of VvCTr1 transcripts in
other grapevine cultivars, namely, “Alvarinho” and “Cabernet Sauvignon” (Martins et al. 2012), supports its function
as a core regulator of copper homeostasis, whose expression is nonetheless finely modulated by environmental factors, including copper stress (Martins et al. 2012). Further
studies on the other VvCTr members and their possible
interactions will contribute to elucidate the roles of CTrs in
regulating copper homeostasis in the grapevine.
Acknowledgments We thank Lola Peñarrubia and Antoni Garcia i Molina for providing the Arabidopsis copt5 line used in
this study. We are grateful to Dennis J. Thiele for providing the
ctr1Δctr3Δctr2Δ and the ctr1Δctr3Δ knock out yeast strains. We
thank Niko Geldner for providing the wave line constructs used
13
Planta (2014) 240:91–101
in this study. We are grateful to Hiromi Tajima for providing the
Remorin constructs. This work was supported by European Union
Funds (FEDER/COMPETE-Operational Competitiveness Program)
- Portuguese Foundation for Science and Technology [FCOMP-010124-FEDER-022692, FCOMP-01-0124-FEDER-008760 (Ref. FCT
PTDC/AGR-ALI/100636/2008), FCT/5955/27/5/2013/S—scientific
cooperation Portugal-Tunisia, PhD grant no. SFRH/BD/64587/2009
to V.M.]; by the networking activities within the European project
INNOVINE [ref. 311775]; by the European COST Action [FA1106
“QualityFruit”] and by the Will W. Lester Endowment University of
California.
Conflict of interest The authors declare that they have no conflict
of interest.
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