Genetic and physiological approaches toward understanding the mechanisms underlying the sulfur-regulated expression of β-conglycinin genes

Abstract

Accumulation of the β subunit of β-conglycinin, a major seed storage protein of soybean, is known to be upregulated by sulfate deficiency and repressed by exogenous application of methionine in the in vitro culture of immature cotyledons. Accumulation of the β subunit mRNA increased in seeds of soybean plants as the concentration of sulfate in the media was decreased. The promoter of the β subunit was capable of upregulation, suggesting that the regulation mainly occurs at the level of transcription. The level of free sulfate in seeds of soybean grown under sulfur deficiency was dramatically reduced. Immature soybean seeds cultured in vitro in a sulfate deficient medium accumulated an elevated level of the β subunit. These results suggest that the level of sulfate concentration in seeds is a main trigger for the induction of the β subunit accumulation in plants exposed to sulfur deficiency. Possible application of genetical approaches for better understanding of the regulation mechanism is discussed.