Moleculaabiological analysis of phytochrome siggnal transduction

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Phytochrome is a chromoprotein which is common in green plants.Phytochrome is know to be act as a major photoreceptor mediating divergent plant responses to light.Although intensive work has been done on phytochrome, molecular mechanism in which phytochrome transduce the light signal to signal transduction factors.We addressed this problem with molecular as well as biochemical techniques in the present study.To examine biological activity of the C-terminal half, which has been speculated to be involved in the signal transduction process, we prepared transgenic Arabidopsis expressing a C-terminal fragment of phytochrome B(phyB).The analysis of those plants indicated that the C-terminal region alone could not interact with the endogenous signal transduction mechanism.Next, we investigated intracellular localization of phyB with the aid of a reporter protein.C-terminal fragments of phyB was fused to GUS reporter protein and expressed in transgenic Arabidopsis.Histochemical staining of GUS activity in those plants revealed that the fusion protein localized to the nucleus.Nuclear localization of endogenous phyB was confirmed by immunoblotting analysis of nuclei isolated from light-grown Arabidopsis.Furthermore, the level of phyB in the isolated nuclei was substantially decreased if plants was irradiated with far-red light and then kept in darkness.Taken together, is possible that nuclear localization of phyB is an important step of phytochrome signaling process.We have also examined biolochemical and biological activity of fern phytochrome expressed in higher plants.The results indicated that the fern phytochrome is photochemically active in higher plants.Nevertheless, it did show only very limited biological activity.So, we concluded that fern phytochrome is structurally too diverse from higher plant phytochrome to transduce the signal in higher plants.