Evidence for the plant‐specific intercellular transport of the Arabidopsis copper chaperone CCH

Abstract

SummaryArabidopsis copper chaperone (CCH) belongs to a family of eukaryotic proteins that participates in intracellular copper homeostasis by delivering this metal to the secretory pathway. In this work we show that the CCH protein is mainly located along the vascular bundles of senescing leaves and petioles, as shown by tissue prints and immunohistochemical detection. CCH protein also accumulates in stem sieve elements and is collected in phloem exudates. Accordingly, Arabidopsis CCH is the only member of the metallochaperone family described to function intercellularly to date. Moreover, the CCH protein remains stable when plants are subjected to excess copper that causes a rapid and speci®c decrease in its mRNA. These facts point to a role for CCH in copper mobilization from decaying organs towards reproductive structures, as a result of metalloprotein breakdown.

Copper Chaperone Antioxidant Protein1 Is Essential for Copper Homeostasis

“…Both CCH and ATX1 are predicted to contribute to Cu homeostasis, and their expression is influenced by Cu availability (Mira et al, 2001a;Puig et al, 2007b). However, whether they affect each other's expression is not known.…”

“…However, CCH has a unique C-terminal extension, whereas ATX1 has a probable N-terminal signal peptide (Mira et al, 2001b). The C-terminal extension of CCH was proposed to be involved in the translocation of proteins through plasmodesmata to nonnucleated cells, such as sieve elements, to provide a symplastic pathway for Cu redistribution and reutilization (Mira et al, 2001a). The mRNA expression of CCH is induced in the absence of Cu and reduced with excess Cu, whereas ATX1 expression is induced by excess Cu.…”

Arabidopsis NPCC6/NaKR1 Is a Phloem Mobile Metal Binding Protein Necessary for Phloem Function and Root Meristem Maintenance

“…HMA domain proteins have been identified in the phloem sap of Brassica napus and Cucurbita maxima (Giavalisco et al, 2006;Lin et al, 2009). In Arabidopsis, HMA domain protein CCH is found in the phloem and is thought to transport Cu out of senescing tissues (Himelblau et al, 1998;Mira et al, 2001). nakr1-1 seedling growth (for 2 weeks) was not affected more than the wild type when Zn 2+ (up to 15 mM) or Cu 2+ (up to 25 mM) was included in the growth medium (data not shown).…”

Arabidopsis Pollen Fertility Requires the Transcription Factors CITF1 and SPL7 That Regulate Copper Delivery to Anthers and Jasmonic Acid Synthesis

“…Recent transcriptome analyses revealed that SPL7 is required for the expression of the iron (Fe)/Cu reductase oxidases, FRO4 and FRO5, and several Cu transporters, including members of the copper transporter family, COPT1 and COPT2, that together constitute the high-affinity Cu uptake system (Bernal et al, 2012;Gayomba et al, 2013;Jung et al, 2012;Yamasaki et al, 2009;Jain et al, 2014). Among other SPL7-regulated genes are COPT6, members of the yellow stripe-like transporter family, YSL2 and YSL3, and the Cu chaperone CCH, which together contribute to Cu transport to photosynthetic tissues and Cu remobilization from sources to sinks upon senescence (Bernal et al, 2012;Gayomba et al, 2013;Jung et al, 2012;Yamasaki et al, 2009;Chu et al, 2010;Himelblau et al, 1998;Mira et al, 2001;Himelblau and Amasino, 2001). The SPL7-dependent Cu economy/metal switch mechanism involves the increased expression of Cu-responsive miRNAs that, in turn, facilitate mRNA degradation of abundant Cu-containing proteins such as Cu/Zn-superoxide dismutase (SOD), CSD1, CSD2, plantacyanin (ARPN), and laccase-like multicopper oxidases (LAC2, LAC3, LAC4, LAC7, LAC12, LAC13, and LAC17) (Abdel-Ghany and Pilon, 2008;Pilon, 2017;McCaig et al, 2005;Ravet et al, 2011;Shahbaz et al, 2015).…”