The CTR/COPT-dependent copper uptake and SPL7-dependent copper deficiency responses are required for basal cadmium tolerance in A. thaliana

Abstract

Copper (Cu) homeostasis in plants is maintained by at least two mechanisms: (1) the miRNA-dependent reallocation of intracellular Cu among major Cu-enzymes and important energy-related functions; (2) the regulation of the expression of Cu transporters including members of the CTR/COPT family. These events are controlled by the transcription factor SPL7 in Arabidopsis thaliana. Cadmium (Cd), on the other hand, is a non-essential and a highly toxic metal that interferes with homeostasis of essential elements by competing for cellular binding sites. Whether Cd affects Cu homeostasis in plants is unknown. We found that Cd stimulates Cu accumulation in roots of A. thaliana and increases mRNA expression of three plasma membrane-localized Cu uptake transporters, COPT1, COPT2 and COPT6. Further analysis of Cd sensitivity of single and triple copt1copt2copt6 mutants, and transgenic plants ectopically expressing COPT6 suggested that Cu uptake is an essential component of Cd resistance in A. thaliana. Analysis of the contribution of the SPL7-dependent pathway to Cd-induced expression of COPT1, COPT2 and COPT6 showed that it occurs, in part, through mimicking the SPL7-dependent transcriptional Cu deficiency response. This response also involves components of the Cu reallocation system, miRNA398, FSD1, CSD1 and CSD2. Furthermore, seedlings of the spl7-1 mutant accumulate up to 2-fold less Cu in roots than the wild-type, are hypersensitive to Cd, and are more sensitive to Cd than the triple copt1copt2copt6 mutant. Together these data show that exposure to excess Cd triggers SPL7-dependent Cu deficiency responses that include Cu uptake and reallocation that are required for basal Cd tolerance in A. thaliana.

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

“…From what is known, genes encoding Cu transporters COPT1, COPT2, COPT3, and COPT6 are expressed in pollen grains of Arabidopsis (Sancenón et al, 2004;Gayomba et al, 2013;Jung et al, 2012;Bock et al, 2006). AtCOPT3 is expressed early in pollen development, while At-COPT1 is expressed at later stages (Bock et al, 2006).…”

“…Both transcription factors (TFs) regulate gene expression during Cu deficiency through binding to Cu deficiency-responsive elements (59-GTAC-39) in promoters of their targets (Sommer et al, 2010;Yamasaki et al, 2009;Quinn et al, 2000;Birkenbihl et al, 2005;Garcia-Molina et al, 2014;Kropat et al, 2005). 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).…”

“…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).…”

“…CSD1 and CSD2 functions are replaced by the Fe-containing SOD, FSD1 (Burkhead et al, 2009). Because of the important role of SPL7 in Cu homeostasis, spl7 mutants accumulate less Cu and develop slower unless Cu is added to the growth medium (Bernal et al, 2012;Yamasaki et al, 2009;Gayomba et al, 2013).…”

Effect of Phosphorus on the Cadmium Transfer and ROS-scavenging Capacity of Rice Seedlings

“…(Barceló et al, 1988;Jung et al, 2015Jung et al, , 2016Lagriffoul et al, 1998;. 특히 카드뮴에 의해 발생된 산화적 스트레스는 활성산소종의 세포 내 축 적으로 인하여 탄수화물, 단백질, 지질 및 핵산의 생합성에 부정적인 영향을 미치고 산화 ․ 환원 항상성을 교란하여 정 상적인 생체 기능을 저해한다 (Gayomba et al, 2013;Singh and Agrawal, 2010;Singh et al, 2006, Xu et al, 2014.…”