Abstract
Phytochromes are encoded by a small multi gene family. Among members of the family, phyA exhibits features that are not observed in other phytochromes. Those include; 1) to mediate very low fluence response, 2) to mediate far-red high irradiance response, 3) rapid light-induced degradation. Those characteristics indicate that phyA evolved as a highly-sensitive phytochrome. To elucidate molecular basis for the phyA specialization, we conducted a phyA/phyB chimeric analysis. Phytochrome molecule was divided into 4 domains (N-PAS, GAF, PHY and C-terminal). All the possible 14 combinations, in which each domain was derived from either phyA or phyB, were expressed in the Arabidopsis phyAphyB mutant. Analysis of the resulting plants revealed that different phyA features based on different combinations of domains. In other word, each domain contributed in a different way to confer phyA specific features. The mechanism of functional diversification of phytochromes will be discussed on the basis of those findings.
