DIFFERENTIAL REGULATION OF SOYBEAN SEED STORAGE PROTEIN GENE PROMOTER-GUS FUSIONS BY EXOGENOUSLY APPLIED METHIONINE IN TRANSGENIC ARABIDOPSIS-THALIANA

Expression of the gene encoding the beta subunit of beta-conglycinin, the 7S seed storage protein of soybean (Glycine max [L.] Merr.), has b een shown to be down-regulated by exogenously applied L-methionine in in vitro soybean cotyledon cultures, whereas expression of the gene en coding the alpha' subunit is not affected. We constructed transgenic A rabidopsis thaliana (L.) Heynh. carrying the beta-glucuronidase (GUS) reporter gene under the control of the promoter regions from either th e alpha' or beta subunit gene. An in vitro culture system of immature siliques of A. thaliana was developed for exogenous application of L-m ethionine to immature seeds. Expression of the beta subunit gene promo ter-GUS fusion was down-regulated by the application of L-methionine, and this response was reversible. As an alternative way to apply L-met hionine, A. thaliana plants were grown on rockwool and irrigated with L-methionine-supplemented medium. GUS activity driven by the beta subu nit gene promoter was repressed by L-methionine, and the degree of rep ression depended on the concentration of L-methionine in the medium. O n the other hand, the alpha' subunit gene promoter-GUS fusion did not show such a response. These results indicate that A. thaliana has a sy stem to differentially regulate the expression of the beta-conglycinin genes by L-methionine at the level of transcription. This work establ ishes a system to genetically analyze plants' responses to nutritional stimuli.