Light-sensing toolkit of cyanobacteria: photoreceptors, signaling and photomorphogenesis

Cyanobacteria, ancient photosynthetic prokaryotes, acclimatize to diverse light conditions. Light is not just an energy source for these organisms but also a crucial environmental signal that governs their growth, physiology, and ecological spread. Cyanobacteria possess a sophisticated system for light detection and response, crucial for their central role in global carbon and nitrogen cycles. The present work covers the complex network of photoreceptors—including phytochrome-like proteins, i.e., cyanobacteriochromes, and rhodopsins—that allow cyanobacteria to sense light. We also explore how the photosynthetic electron transport chain acts as a redox-sensitive system to regulate photosystem activity in response to light quality and intensity. The key focus will be on the mechanisms of light acclimation, particularly chromatic acclimation, where cyanobacteria remodel their light-harvesting complex (phycobilisomes) to optimize light absorption. In the last, we examine how signaling pathways, such as the RcaE-RcaF-RcaC and CcaS-CcaR systems, regulate acclimation to light. By understanding how cyanobacteria integrate light perception and photomorphogenesis, this work offers insights into their ecological resilience and provide opportunities for biotechnological applications in synthetic biology.