Abstract

Phytochromes are photoreceptors that regulate many aspects of plant growth and development in response to red/far-red light signals from the environment. ^1–3 Phytochromes in higher plants are encoded by small gene families. ⁴ For example, the completed whole genome sequences of Arabidopsis thaliana and Oryza sativa phytochromes reveal five (PHYA to PHYE) and three (PHYA to PHYC) genes, respectively. ^5,6 Phytochromes are dimeric chromoproteins having covalently linked open tetrapyrrole phytochromobilin and exist in two photochromic species, red-light-absorbing Pr and far-red-light-absorbing Pfr forms. They are biosynthesized as the Pr form in the dark, which can be phototransformed into the Pfr form upon exposure to red light. The Pr-to-Pfr phototransformation of phytochromes induces the highly regulated signaling network for photomorphogenesis in plants. ^7–9 Recent studies on the molecular mechanisms of the phytochrome-mediated light signaling reveal that phytochrome photoactivation impacts on the control of protein subcellular localization, ^10,11 transcription, ^12,13 protein stability, ^14,15 and protein phosphorylation. ¹⁶ Here, we highlight the current knowledge about the molecular mechanisms of phytochrome function based on the recent advances.