Summary

Photoreceptors are present in all kingdoms of life. They fulfill a broad range of functions, including vision, photoprotection, and regulating growth and development (1). To maintain photosensitivity, photoreceptor-mediated signaling must be turned on and off in a timely fashion. For example, the signaling state of human visual rhodopsins is very short-lived, and patients with defective rhodopsin inactivation suffer from severe dark adaptation problems, illustrating the importance of inactivation mechanisms (2). On page 343 of this issue, Wang et al. (3) report a mechanism of controlling the signaling activity of a family of photoreceptors in plants. They show that cryptochromes are activated through blue light–induced homodimerization. This dimerization and all subsequent signaling events are blocked by the interaction between light-activated cryptochrome and a protein coined BLUE-LIGHT INHIBITOR OF CRYPTOCHROMES 1 (BIC1) (3). This system is proposed to control the fraction of cryptochrome photoreceptors engaged in cellular signaling, contributing to the maintenance of photosensitivity.