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 β subunit of β-conglycinin, the 7S seed storage protein of soybean (Glycine max [L.] Merr.), has been shown to be down-regulated by exogenously applied L-methionine in in vitro soybean cotyledon cultures, whereas expression of the gene encoding the a′ subunit is not affected. We constructed transgenic Arabidopsis thaliana(L.) Heynh. carrying the β-glucuronidase (GUS) reporter gene under the control of the promoter regions from either the a′ or β subunit gene. An in vitro culture system of immature siliques of A. thaliana was developed for exogenous application of L-methionine to immature seeds. Expression of the fi subunit gene promoter-GUS fusion was down-regulated by the application of L-methionine, and this response was reversible. As an alternative way to apply L-methionine, A. thaliana plants were grown on rockwool and irrigated with L-methionine-supplemented medium. GUS activity driven by the β subunit gene promoter was repressed by L-methionine, and the degree of repression depended on the concentration of L-methionine in the medium. On the other hand, the a′ subunit gene promoter-GUS fusion did not show such a response. These results indicate that A. thaliana has a system to differentially regulate the expression of the β-conglycinin genes by L-methionine at the level of transcription. This work establishes a system to genetically analyze plants′ responses to nutritional stimuli.