Genetic analyzes of seed storage protein gene expression in response to environmental stimuli

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beta-Conglycinin, one of the major seed storage protein of soybean, consists mainly of three subunits, namelyalpha, alpha' and beta.Among these, the beta subunit is unique because its expression is enhanced under sulfate deficiency and repressed in the presence of methionine.Transgenic Arabidopsis thaliana, SNTbeta3, which carries the beta-glucuronidase (GUS) gene fused to the promoter of the betasubunit gene was constructed.An A.thaliana mutant, mto1-1, accumulates 10- to 40-fold higher concentration of soluble methionine in rosette leaves during the vegetative growth period.However, once the mutant plants started to flower, the concentration of soluble methionine in rosette leaves become low and the mutant plants accumulate soluble methionine in immature fruits and the apex region.At 40 days after imbibition, the mutant plants accumulated about 5-fold higher concentration of soluble methionine in these sink organs.An A.thaliana line that is homozygous for both the mto1-1 mutation and the transgene was constructed (SNTbeta3mto).GUS activity in seeds of SNTbeta3mto plants was 1/40 of that of SNTbeta3 seeds.Reciprocal crosses were made between SNTbeta3 and the mto1-1 mutant plants and the GUS activity was measured in the F1 seeds.The results indicated when the mto1-1 mutant plants were the mother, GUS activity in F1 seeds was repressed while there was no apparent difference in the GUS activity in the reverse cross as compared to the control cross in which wildtype plants were used in place of the mto1-1 mutant plants.These results suggest that soluble methionine translocated from the mother plants regulates the beta subunit promoter activity in seeds.