Abstract
PHY3/neo1 photoreceptor is composed of both a phytochrome photosensory domain and a full-length phototropin. Red and/or blue light signals received by PHY3 are transmitted downstream through protein kinase activity located in the PHY3 phototropin region. In Arabidopsis phot1, light-dependent FMN-Cys adduct formation in LOV2 leads to a conformational change that results in releasing the kinase domain from the dark-lid-state. Several amino acids that show an important role for this structural change have been identified in Arabidopsis phot1. To study molecular mechanisms for light-dependent kinase domain activation of PHY3, mutations were introduced in such critical amino acids conserved in PHY3, and resultant mutated-PHY3s were transferred into the Arabidopsis phot1phot2 mutant. Phototropic responses of these transgenic Arabidopsis indicated that light-dependent FMN-Cys adduct formation is not necessary for PHY3 kinase domain activation, suggesting there would be another activation mechanisms in PHY3 that were different from ones of higher plant phototropins.
