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.

中文翻译：

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铜激活的蛋白酶调节蓝细菌中的光合可溶性电子载体

GEO的铁利用率大大降低后，光合生物进化出了几种替代蛋白。这些蛋白之一是质体蓝蛋白，一种I型蓝铜蛋白，能够代替细胞色素c6作为细胞色素b6f和PSI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利用率的调节，但调节系统仍然未知。在这里，我们显示该调节是由蛋白酶系统介导的，该蛋白酶系统由抑制petE并激活petJ表达的BlaI / CopY转录因子（PetR）和降解PetR的BlaR膜蛋白酶（PetP）组成。使用体外检测系统同时检测蓝藻在PCC 6803和大肠杆菌中，我们显示PetP直接降解PetR，并且需要铜的存在，这表明它可以直接检测铜。此外，使用RNA-seq，我们显示PetR仅调控Synechocystis sp PCC 6803中的4个基因（petE，petJ，slr0601和slr0602）。