Multisensing photoreceptors: a cross-kingdom perspective

Photoreceptors are classically depicted as monochromatic switches governed strictly by light. However, emerging biophysical and structural insights reveal that these proteins act as dynamic, multisensory hubs across kingdoms of life. Drawing primarily on plant and fungal systems, where mechanisms are most extensively characterized, this review synthesizes how photoreceptors integrate ambient temperature and cellular oxidative state alongside photon flux, with cross-kingdom examples extending this framework to bacteria. Thermal energy modulates dark reversion rates, quaternary assembly, and photobody phase separation, whereas reactive oxygen species alter the photocycle and trigger structural shifts through direct redox sensing. Under a ‘stress-first' evolutionary model, ancestral stress-sensing scaffolds could be retrofitted with chromophores via exaptation, providing a unified biophysical rationale for how cells decode complex, fluctuating environments.