Abstract
The fern Adiantum capillus-veneris has a chimera photoreceptor, phytochrome3 (phy3), which has high homologies to a phytochrome in N terminus and a phototropin in C terminus. We isolated mutants deficient in red light-induced phototropic response. Mutational analysis and complementation revealed that the function of phy3 is both for red light-induced phototropism and for red light-induced chloroplast photorelocation. phy3 does not exist in Arabidopsis and no information about phy3 was reported from any plants other than Adiantum. So, we looked for PHY3 sequences in several fern species and PHY3-homologous sequences were found within the polypodiaceousferns, but not in the more primitive ferns such as Osmunda and Lygodium. Since phy3 greatly enhances the sensitivity to white light in orienting young leaves, this chimeric photoreceptor may have played a key role in the divergence and proliferation of fern species under low-light canopy conditions.
