Control of transcription and mRNA turnover as mechanisms of metabolic repression of α‐amylase gene expression

Abstract

Carbon metabolites suppress the expression of α‐amylase genes in germinating seeds and in suspension‐cultured cells of rice. We have used suspension cell culture as a model system to study the mechanisms of metabolic regulation of α‐amylase gene expression in rice. Both transcription rate and mRNA stability increased as cells were starved of sucrose; the transcription rate of α‐amylase genes in cells starved of sucrose for 24 h was seven times greater than in cells provided with sucrose. The half‐life of α‐amylase mRNA was less than 1 h in cells provided with sucrose, but increased to 12 h in cells starved of this sugar. A protein synthesis inhibitor, cycloheximide (CHX), induced massive accumulation of a‐amylase mRNA in cells provided with sucrose. The longer half‐life of mRNA induced by sucrose starvation and the massive accumulation of mRNA caused by CHX were specific to the α‐amylase genes, since actin genes were not similarly affected. Our findings suggest that both transcriptional and post‐transcriptional control mechanisms are important in the metabolic regulation of α‐amylase gene expression and de novo synthesized proteins are involved in these mechanisms. The expression of α‐amylase and actin genes is regulated in an opposite manner by sugars, which also suggests the operation of a differential regulatory mechanism under different growth conditions.