The evolution and function of blue and red light photoreceptors.

Photoreceptors allow living organisms to optimize perception of light in the natural environment and thus to gain information about their external world. In this review, we describe blue and red light photoreceptors in bacteria, plants, and animals in relation to their evolution. Analyses performed in different organisms have revealed wonderful examples of structural modifications of the light-sensing proteins themselves, as well as diversification of the signal transduction pathways they use in relation with their evolutionary history and function. In different organisms, the same photoreceptor may have a very conserved role (convergent evolution of function) or may modulate different responses (acquisition of new function). Multiple photoreceptors of the same family in the same organism indicate gene duplication events during evolution, with a consequent enhanced sensitivity to variations in ambient light. Conversely, two different photoreceptors may be involved in the control of the same physiological response. Genomic analysis in marine diatoms, combined with phylogenetic studies, has also revealed the presence of blue and red light photoreceptors in the marine environment. This discovery has intriguing implications for the understanding of light perception and its evolution in photosynthetic organisms. In addition, the characterization of these photoreceptors likely will add to our understanding of photoreceptor diversity as an adaptation to different habitats.