After the Great Oxidation Event (GOE), iron availability was greatly decreased, and photosynthetic organisms evolved several alternative proteins and mechanisms. One of these proteins, plastocyanin, is a type I blue-copper protein that can replace cytochrome c₆ as a soluble electron carrier between cytochrome b₆f and photosystem I. In most cyanobacteria, expression of these two alternative proteins is regulated by copper availability, but the regulatory system remains unknown. Herein, we provide evidence that the regulatory system is composed of a BlaI/CopY-family transcription factor (PetR) and a BlaR-membrane protease (PetP). PetR represses petE (plastocyanin) expression and activates petJ (cytochrome c₆), while PetP controls PetR levels in vivo. Using whole-cell extracts, we demonstrated that PetR degradation requires both PetP and copper. Transcriptomic analysis revealed that the PetRP system regulates only four genes (petE, petJ, slr0601, and slr0602), highlighting its specificity. Furthermore, the presence of petE and petRP in early branching cyanobacteria indicates that acquisition of these genes could represent an early adaptation to decreased iron bioavailability following the GOE.

大氧化事件（GOE）之后，铁的利用率大大降低，光合生物进化出了几种替代蛋白质和机制。其中一种蛋白，质体蓝蛋白，是一种I型蓝铜蛋白，可以代替细胞色素c ₆作为细胞色素b ₆ f和光系统I之间的可溶性电子载体。在大多数蓝细菌中，这两种替代蛋白的表达受铜的可利用性调节，但监管系统仍然未知。在本文中，我们提供证据表明调节系统由BlaI / CopY家族转录因子（PetR）和BlaR膜蛋白酶（PetP）组成。PetR抑制petE（质体蓝蛋白）表达并激活petJ（细胞色素c ₆），而PetP控制体内的PetR水平。使用全细胞提取物，我们证明了PetR降解需要PetP和铜。转录组分析显示，PetRP系统仅调控四个基因（petE，petJ，slr0601和slr0602），突出了其特异性。此外，早期分支的蓝细菌中petE和petRP的存在表明，这些基因的获得可能代表了GOE后对铁生物利用度降低的早期适应。