Joint study on the search for phytochrome-binding protein

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We have cloned 4 phytochrome genes and 3 cDNAs of them from fern Adiantum capillus-veneris. One of the sequences has a quite unique structure, i.e.N-terminus half of the gene has a conventional phytochrome structure, but C-terminus half has a structure of typical protein kinase. We also cloned and sequenced 5 genes and their cDNAs of blue light receptors. One of them has a predicted trans-membrane segment, indicating the protein encoded by this gene might localize in the plasma membrane and mediate chloroplast photoorientaion of apical swelling of protonemata. The photoreceptive site of these phenomena were found to be localized in the plasma membrane. We think that almost all photoreceptors involving the photomorphogenesis in fern are now in our hands. We are now characterizing which photoreceptor mediates which photoresponses, and we hope that we will dissolve signal transduction pathways of these photoreceptors in the near future.Red light induced gene expression was revealed in the first time in spore germination. Gene expression of light harvesting chlorophyll binding protein (Lhcb) was controlled by phytochrome, and red/farred photoreversibility was shown.Side branch formation in protonemata of the moss Ceratodon purpureus was found to be mediated by phytochrome. The frequency of red-light-induced branch formation differed between cells of differeny ages. The position of branching within the cell depended on the high absorption of red light. An aphototropic mutant ptr 116 which is deficient of biosynthesis of phytochrome chromophore, showed no branch formation by red light but was rescued by supplement of biliverdin, a precursor of phytochrome chromophore, in the culture medium.