Umemura T a, Perata P, Futsuhara Y, Yamaguchi J
Meijo University, Nagoya, Japan.
Planta. 1998 Apr;204(4):420-8. doi: 10.1007/s004250050275.
We used a transient expression system to study the mechanism by which carbohydrates repress a rice (Oryza sativa L.) alpha-amylase (EC 3.2.1.1) gene. Exogenously fed metabolizable carbohydrates are able to elicit repression of the alpha-amylase gene RAmy3D in the rice embryo, and our results indicate that repression is also triggered efficiently by endogenous carbohydrates. Glucose analogs that are taken up by plant cells but not phosphorylated by hexokinase are unable to repress the alpha-amylase gene studied, while 2-deoxyglucose, which is phosphorylable but not further metabolized, down-regulates RAmy3D promoter activity, indicating a role for hexokinase in the sugar-sensing mechanism triggering repression of the RAmy3D gene. We tested two different hexokinase inhibitors, mannoheptulose and glucosamine, but only the latter was able to relieve RAmy3D promoter activity from repression by endogenous carbohydrates. This correlates with the higher ability of glucosamine to inhibit the activity of rice hexokinases in vitro. The glucosamine-mediated relief of RAmy3D promoter activity from repression by endogenous carbohydrates does not correlate with a reduced rate of carbohydrate utilization.
我们使用瞬时表达系统来研究碳水化合物抑制水稻（Oryza sativa L.）α-淀粉酶（EC 3.2.1.1）基因的机制。外源供给的可代谢碳水化合物能够引发水稻胚中α-淀粉酶基因RAmy3D的抑制，并且我们的结果表明内源碳水化合物也能有效地触发抑制作用。被植物细胞摄取但不被己糖激酶磷酸化的葡萄糖类似物无法抑制所研究的α-淀粉酶基因，而可被磷酸化但不能进一步代谢的2-脱氧葡萄糖则下调RAmy3D启动子活性，这表明己糖激酶在触发RAmy3D基因抑制的糖感知机制中起作用。我们测试了两种不同的己糖激酶抑制剂，甘露庚酮糖和葡糖胺，但只有后者能够解除内源碳水化合物对RAmy3D启动子活性的抑制。这与葡糖胺在体外抑制水稻己糖激酶活性的能力较强有关。葡糖胺介导的内源碳水化合物对RAmy3D启动子活性抑制的解除与碳水化合物利用速率的降低无关。
