Photoreception (light detection) is one of the most important sensory systems that plays a vital role in the survival of most species, where photons are absorbed by an array of photosensitive molecules found in both eukaryotes and prokaryotes. Despite the presence of a common photoreceptive function across many classes of organisms on Earth, the receptors and signalling pathways involved, and their evolutionary origins, are diverse. For example, in animals, light is generally detected via photopigments that consist of an opsin protein bound to a retinal-based chromophore. Over time, these pigments have evolved to detect a wide spectrum of light (~300-700 nm). Insects, which also utilize retinal-based pigments, use Type I cryptochromes to detect light directly, whereas mammalian cryptochromes (Type II) do not: instead, these latter proteins are critical components of the circadian clock machinery. In plants, phytochromes and cryptochromes have evolved to detect long (red) and short (blue) wavelengths of light, respectively.

While some photoreceptor molecules have been studied in detail, other systems have not. For example, in vertebrates, five pigment classes have evolved to detect specific ranges of wavelengths, whose information is collated by the brain to form a colored image of the visual landscape. Conversely, the role of irradiance detection in non-visual systems is poorly understood, except for the regulation of circadian rhythms via melanopsin-expressing biosensor cells.

The aim of this Research Topic is to provide an update on the breadth and depth of research currently in progress that relates to a better understanding of the multiplicity of photosensory systems observed in organisms that range from bacteria to plants and animals. Such an approach should highlight the diverse and convergent ways in which organic life utilizes light to both regulate physiology and sense the local environment. Research papers that present new data or review work from molecular to behavioural levels are welcomed.

Important Note: All contributions to this Research Topic must be within the scope of the section and journal to which they are submitted, as defined in their mission statements. Frontiers reserves the right to guide an out-of-scope manuscript to a more suitable section or journal at any stage of peer review.