Plastoquinone’s pivotal role in photosynthesis and redox sensing: a thylakoid redox hub for chloroplast and cyanobacterial signaling

Photosynthesis is the fundamental light-driven process where photoautotrophs convert carbon dioxide into sugars. The necessary reducing power is generated by the Photosynthetic Electron Transport Chain (PETC), which takes place in the thylakoid membrane. The mobile electron carrier Plastoquinone (PQ) is central to this process. The PQ reduction-oxidation cycle is not only the rate-limiting step of photosynthesis but also a key control point for PETC activity. Beyond its role in electron transport, PQ acts as a crucial redox sensor, initiating gene expression pathways related to photosynthesis and environmental stress. Furthermore, the redox state of PQ governs distinct non-photosynthetic functions; non-photoreducible PQ serves as a stress-response reservoir in plants and algae, while photoreducible PQ helps to regulate circadian rhythm in cyanobacteria. These diverse roles underscore PQ’s pivotal importance in sensing the external light environment and enabling photoprotection. This review examines the various roles of PQ in cyanobacteria, algae, and higher plants, extending beyond its well-established function in photosynthesis. Additionally, we will discuss how controlling the redox state of PQ can be strategically applied for biomanufacturing purposes, including its potential in Biophotovoltaics (BPV) technology for generating photocurrent.