| Copper is one of the essential micronutrients for most living organisms. In higher plants, copper is mainly utilized as a cofactor of proteins involved in photosynthesis as a plastocyanin, and scavenging of reactive oxygen species as a copper/zinc superoxide dismutase (Cu/Zn SOD). A green alga, Chlamydomonas reinhardtii, adapts to copper depletion by switching the photosynthetic apparatus from plastocyanin to cytochrome c6 containing iron. This regulation is mediated by a single transcription factor, Crr1 (Copper response regulator 1). In contrast, a land plant, Arabidopsis thaliana, adjusts to copper deficiency by modifying the reactive oxygen species scavenging system from Cu/Zn SOD to Fe SOD containing iron and this down-regulation of Cu/Zn SOD is mediated by microRNA, miR398. Previously we identified SPL7 (SQUAMOSA promoter binding protein-like 7), an ortholog of Crr1, as a transcription activator for miR398. In addition SPL7 also activates some genes involved in copper homeostasis, including Fe SOD in copper deficient conditions. We propose that SPL7 is a master regulator for copper homeostasis in Arabidopsis During evolution, the master regulator of copper homeostasis has been conserved, but the strategies for adapting to copper deficiency became divergent among organisms so that they could adapt to different environments. |