Heliorhodopsin evolution is driven by photosensory promiscuity in monoderms

We bring to resolution the debated monoderm/diderm occurrence patterns and show that HeRs are restricted to monoderms. Moreover, we provide compelling evidence that HeRs are a novel type of sensory rhodopsins linked to histidine kinases and other two-component system genes across phyla. Additionally, we also describe two novel putative signal-transducing domains fused to some HeRs. We posit that HeRs likely function as generalised light-dependent switches involved in the mitigation of light-induced oxidative stress and metabolic circuitry regulation.