ANALYSES OF FACTORS INVOLVING BOTH LIGHT SIGNALLING AND REGULATION OF G-PROTEIN ACTIBITY IN PLANT.

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In 1997 and 1998, we isolated and characterized a GDI (GTPase dissociation inhibitor) homolog that was isolated as ARA2 binding protein. In collaboration with Dr.Takashi Ueda at RIKEN, we designated this gene as GD12 and this GD12 protein can also regulated GTPase activity by specific binding with ARA2 protein.In 1999 and 2000, we analysed GTP-binding protein in combination with light signal transduction. At the beginning of this experiment, we were using Arabidopisis but later we used the rice mutant of trimeric Ga-subunit, Daikoku Dwarfs in collaboration with Dr.Iwasaki at Fukui prerf.Univ. and Dr.Inagaki at NIAR.We investigated expressions of light-inducible genes under monochromatic light conditions. Dariku Dwarfs were isolated from several rice ecotype background and have purple siliques and drarf phenotype as observed in Arabidopsis photomorpheogenesis mutants fusca.We found 1) Expression of LHCB gene was downregulated in Daikoku Dwarf compared with isogenic wild type under continuous red light conditions. 2) Induction of LHCB gene expression by short period far-red light irradiation, was lower in Daikoku mutant compared with wild type.3) Expression and induction of CP26 gene was reversibley regulated by red/far-red light in Nipponbare. But, in DK22, a Daikoku mutant, showed no reversible expression by red/far-red light.From these results Ga may be involved in regulation of light-inducible gene through phytochrome mediated light signal transduction.