MicroRNA-mediated Systemic Down-regulation of Copper Protein Expression in Response to Low Copper Availability in Arabidopsis

Abstract

In plants, copper is an essential micronutrient required for photosynthesis. Two of the most abundant copper proteins, plastocyanin and copper/zinc superoxide dismutase, are found in chloroplasts. Whereas plastocyanin is essential for photo-autotrophic growth, copper/zinc superoxide dismutase is dispensable and in plastids can be replaced by an iron superoxide dismutase when copper is limiting. The down-regulation of copper/zinc superoxide dismutase expression in response to low copper involves a microRNA, miR398. Interestingly, in Arabidopsis and other plants, three additional microRNA families, miR397, miR408, and miR857, are predicted to target the transcripts for the copper protein plantacyanin and members of the laccase copper protein family. We confirmed the predicted targets of miR397, miR408, and miR857 experimentally by cleavage site analysis. To study the spatial expression pattern of these microRNAs and the effect of copper on their expression, we analyzed Arabidopsis grown hydroponically on different copper regimes. On low amounts of copper the plants accumulated miR397, miR408, and miR857. The microRNA expression pattern was negatively correlated with the accumulation of transcripts for plantacyanin and laccases. Furthermore, the expression of other laccases that are not predicted targets for known microRNAs was similarly regulated in response to copper. For some of these laccases, the regulation was disrupted in a microRNA maturation mutant (hen1-1), suggesting the presence of other copper-regulated microRNAs. Thus, in Arabidopsis, microRNA-mediated down-regulation is a general mechanism to regulate nonessential copper proteins. We propose that this mechanism allows plants to save copper for the most essential functions during limited copper supply.

Analysis of biochemical variations and microRNA expression in wild (Ipomoea campanulata) and cultivated (Jacquemontia pentantha) species exposed to in vivo water stress

“…Similar to this report, the expression of five miRNA families (miR398, miR408, miR395, miR319 and miR172) differed between I. campanulata and J. pentantha. miR398, miR408 and miR395 largely regulate the expression of genes coding for CuZnSODs (CSD), plantacyanin, and sulfate transport and assimilation (APS; ATP sulfurylases and SULTR; sulfate transporter) respectively, which are also associated with stress responses in plants (Sunkar et al 2006;Abdel-Ghany and Pilon 2008;Jones-Rhoades et al 2006). miR319 targets TCP transcription factor that controls leaf morphogenesis (Palatnik et al 2003).…”

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

“…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).…”

Optimal copper supply is required for normal plant iron deficiency responses

“…A physiological role for this switch from FeSODs to CuSODs was demonstrated, because inability to make this switch resulted in decreased ability to counteract oxidative stress. 11 Additionally, certain microRNAs that are known to be regulated by Cu and to target transcripts of Cu-containing proteins [15][16][17][18] were also regulated by Fe. 11 Fe-Cu crosstalk may also influence mineral transport and uptake.…”