Metabolic derepression of alpha-amylase gene expression in suspension-cultured cells of rice.
We present evidence to show that the alpha-amylase gene family in rice is under two different modes of regulation: 1) hormonal regulation in germinating seeds, and 2) metabolic repression in cultured cells by available carbohydrate nutrients. Expression of alpha-amylase genes in deembryoed rice seeds is known to be induced by exogenous gibberellic acid. On the other hand, expression of alpha-amylase genes in suspension-cultured cells is induced by the deprivation of carbohydrate nutrient. A lag period of 2-4 h is required for the induction of alpha-amylase mRNA in sucrose-depleted medium. The induction of alpha-amylase expression is extraordinarily high and levels of alpha-amylase mRNA can be increased 8-20-folds after 24 h of sucrose starvation. The synthesis and secretion of alpha-amylase is also dependent upon the level of carbon source. The derepression or repression of alpha-amylase synthesis can be readily reversed by the deprivation or replenishment of sucrose in the medium, respectively. Glucose and fructose exert a repression on the alpha-amylase synthesis similar to that of sucrose. A hypothesis that explains the induction of alpha-amylase synthesis by carbohydrate starvation is proposed. Our data have suggested a hitherto undiscovered, potentially important control mechanism of carbohydrate metabolism in higher plants.
Institute of Molecular Biology, Academia Sinica, Taipei, Taiwan, Republic of China.
S M
SM
Yu
Y H
YH
Kuo
G
G
Sheu
Y J
YJ
Sheu
L F
LF
Liu
D015152:Blotting, Northern; D050260:Carbohydrate Metabolism; D002478:Cells, Cultured; D005786:Gene Expression Regulation / Q000187:drug effects; D005875:Gibberellins / Q000494:pharmacology; D066298:In Vitro Techniques; D012275:Oryza / Q000235:genetics* / Q000378:metabolism; D010940:Plant Proteins / Q000235:genetics*; D012333:RNA, Messenger / Q000235:genetics; D000516:alpha-Amylases / Q000235:genetics* / Q000378:metabolism
D005875:Gibberellins; D010940:Plant Proteins; D012333:RNA, Messenger; C007842:gibberellic acid; D000516:alpha-Amylases