1. Department of Molecular, Cell & Developmental Biology, University of California, Los Angeles, California 90095, USA
2. Biology Department, University of Leicester, Leicester LE1 7RH, UK
3. Present address: Genomic Analysis Laboratory, The Salk Institute for Biological Studies, 10010 N. Torrey Pines Road, La Jolla, California 92037, USA.

Correspondence to: Chentao Lin¹ Correspondence and requests for materials should be addressed to C.L. (e-mail: Email: clin@mcdb.ucla.edu).

Abstract

Cryptochromes are blue/ultraviolet-A light receptors that mediate various light responses in plants and animals^{1, 2}. But the initial photochemical reaction of cryptochrome is still unclear. For example, although most photoreceptors are known to undergo light-dependent protein modification such as phosphorylation^{3, 4}, no blue-light dependent phosphorylation has been reported for a cryptochrome. Arabidopsis cryptochrome 2 (cry2) mediates light regulation of seedling development and photoperiodic flowering^{5, 6}. The physiological activity and cellular level of cry2 protein are light-dependent^{5, 6, 7, 8}, and protein–protein interactions are important for cry2 function^{9, 10}. Here we report that cry2 undergoes a blue-light-dependent phosphorylation, and that cry2 phosphorylation is associated with its function and regulation. Our results suggest that, in the absence of light, cry2 remains unphosphorylated, inactive and stable; absorption of blue light induces the phosphorylation of cry2, triggering photomorphogenic responses and eventually degradation of the photoreceptor.