Abstract
Adiantum phytochrome3 (phy3) is a chimeric photoreceptor that contains both phytochrome and phototropin sequences and controls red light-induced phototropism and chloroplast photorelocation movement. phy3 has a serine/threonine kinase domain in its phototropin-related region. To examine the role of the kinase domain in phy3 signaling, we carried out biochemical and physiological analyses. We tested the kinase activity of a GST-kinase domain fusion protein expressed in E. coli and showed that the recombinant protein has autophosphorylation activity. Replacement of histidine at position 1183 (located in the kinase subdomain IV) by leucine (H1183L) impaired the autophosphorylation activity. Introduction of a PHY3(H1183L)-GFP fusion gene into prothallial cells of a PHY3-deficient mutant of Adiantum could not restore red light-induced chloroplast accumulation, whereas that of the wild-type PHY3-GFP fusion gene could complement the response. These results suggest that the phosphorylating activity of the phy3 kinase domain is involved in this phy3-mediated response.
