MATERNAL EFFECTS OF MTO1 MUTATION, THAT CAUSES OVERACCUMULATION OF SOLUBLE METHIONINE, ON THE EXPRESSION OF A SOYBEAN BETA-CONGLYCININ GENEPROMOTER-GUS FUSION IN TRANSGENIC ARABIDOPSIS-THALIANA

beta-Conglycinin, the 7S seed storage protein of soybean (Glycine max [L.] Merr.), is comprised mainly of three subunits, designated alpha, alpha' and beta. Expression of the gene encoding the beta subunit is u nique because its expression has been shown to be down-regulated by ex ogenously applied L-methionine in immature soybean cotyledon cultures in vitro. Arabidopsis thaliana strain carrying a mto1-1 mutation overa ccumulates soluble methionine. By using this mutant, we analyzed the e ffects of methionine on expression of the beta subunit gene in vivo. R eciprocal crosses were made between the mto1-1 mutant and a transgenic A. thaliana strain, designated SNT/beta 3, which carries a beta-glucu ronidase (GUS) reporter gene under the control of the promoter region of the beta subunit gene. Analysis of GUS activity in F-1 seeds indica ted that the GUS activity was dramatically repressed when the mto1-1 m utant plants were used as female parents. We constructed a strain whic h carries both the transgene and mto1-1 mutation in the homozygous sta te. Analyses of the GUS activity in seeds of this double homozygous st rain indicated that the GUS activity was repressed to 2.5% of control by introduction of the mto1-1 mutation. These results indicate that th e beta subunit gene promoter activity in seeds is down-regulated by ma ternal genotype and suggest that soluble methionine, or its mobile met abolite, is translocated from mother plants to repress beta subunit ge ne expression in seeds.