Molecular Genetic Study of Plant Organogenesis and Stimulus-Response Interactions Using Arabidopsis.

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1.Analysis of gene function working in early steps of flower organogenesis. We have examined DNA-binding activity and the specific binding DNA sequences of a floral homeotic gene, AGAMOUS.In vitro binding study has revealed the protein binds to CC(A/T)_6GG as a homodimer. We are now searching for genes whose transcription is controlled by AGAMOUS.We have constructed transgenic Arabidopsis carrying whole cDNA sequences, MADS region, or K region of AGAMOUS gene. Floral structure of the transgenic lines mimics the flowers of other flower mutants, indicating that MADS box and K box are functional domains of AGAMOUS protein, and that the domains may work as binding regions to DNA or to other proteins.2.Identification of floral-bud specific low-abundant genes. We have constructed cDNA libraries from young floral buds of Arabidopsis, and screened low-abundant clones using cold-plaque procedure. Some of the clones are amidoribosyltransferase, akey enzyme of purine biosynthesis. Other clones encode LEA proteins.3.Characterization of tropism-specific proteins. We have examined proteins newly synthesized in roots when exposed to physical or chemical stimuli, gravity, light, touching, heat, abscisic acid, etc., and identifiednearly 20 proteins whose amount is increased by the stimuli.Construction of transgenic Arabidopsis plants and isolation of tagged mutants. We have constructed nearly 2000 transgenic Arabidopsis lines, and screened tagged mutants with altered floral suructure or with altered root structure or root tropic response. We identified several mutant lines and are now studying to isolate the mutated genes.