Sun Jin-Yue, Chen Ye-Miao, Wang Qing-Mei, Chen Jia, Wang Xue-Chen
College of Biological Sciences, China Agricultural University, The State Key Laboratory for Plant Physiology and Biochemistry, Beijing 100094, PR China.
Int J Biochem Cell Biol. 2006;38(7):1102-13. doi: 10.1016/j.biocel.2005.11.013. Epub 2005 Dec 20.
Although triose phosphate/phosphate translocator is known to play an important role in regulating the distribution of assimilates in wheat chloroplasts, the mechanism of triose phosphate/phosphate translocator gene control has not yet been clearly elucidated. We first showed that glucose inhibited the expression of triose phosphate/phosphate translocator gene in wheat by reverse transcription-polymerase chain reaction and Western blotting. The triose phosphate/phosphate translocator expression was seriously impaired by 5 mmol/L glucose, and it responded slowly, more than 48 h, to level as low as 1 mmol/L glucose. Both glucose and 2-deoxyglucose inhibited the expression of triose phosphate/phosphate translocator gene, but 2-deoxyglucose-6-P, product of phosphorylated 2-deoxyglucose, cannot be further metabolized, therefore the further metabolism of phosphorylated glucose by hexokinase is not a prerequisite for triggering glucose-regulated expression of triose phosphate/phosphate translocator gene. Glucose had little inhibitory effect on the expression of triose phosphate/phosphate translocator gene when hexokinase activity was reduced or eliminated by transforming wheat protoplasts with a hexokinase antisense construct or treating protoplasts with glucosamine, an inhibitor of hexokinase. Therefore, it appears essential for hexokinase to retain phosphorylation activity for glucose to regulate the expression of triose phosphate/phosphate translocator gene. The treatment of protoplasts with glucose-6-phosphate resulting in no inhibition of triose phosphate/phosphate translocator expression demonstrated that phosphorylation via hexokinase is necessary for glucose inhibiting triose phosphate/phosphate translocator expression. All the data suggest that triose phosphate/phosphate translocator is regulated by glucose via a hexokinase-dependent pathway.
尽管已知磷酸丙糖/磷酸转运体在调节小麦叶绿体中同化物的分配方面发挥重要作用，但磷酸丙糖/磷酸转运体基因的控制机制尚未得到明确阐明。我们首先通过逆转录-聚合酶链反应和蛋白质免疫印迹法表明，葡萄糖抑制了小麦中磷酸丙糖/磷酸转运体基因的表达。5 mmol/L的葡萄糖会严重损害磷酸丙糖/磷酸转运体的表达，并且它对低至1 mmol/L葡萄糖的反应缓慢，超过48小时。葡萄糖和2-脱氧葡萄糖都抑制磷酸丙糖/磷酸转运体基因的表达，但磷酸化的2-脱氧葡萄糖的产物2-脱氧葡萄糖-6-磷酸不能进一步代谢，因此己糖激酶对磷酸化葡萄糖的进一步代谢不是触发葡萄糖调节磷酸丙糖/磷酸转运体基因表达的先决条件。当通过用己糖激酶反义构建体转化小麦原生质体或用己糖激酶抑制剂氨基葡萄糖处理原生质体来降低或消除己糖激酶活性时，葡萄糖对磷酸丙糖/磷酸转运体基因的表达几乎没有抑制作用。因此，己糖激酶保留对葡萄糖的磷酸化活性似乎对于调节磷酸丙糖/磷酸转运体基因的表达至关重要。用6-磷酸葡萄糖处理原生质体不会抑制磷酸丙糖/磷酸转运体的表达，这表明通过己糖激酶的磷酸化是葡萄糖抑制磷酸丙糖/磷酸转运体表达所必需的。所有数据表明，磷酸丙糖/磷酸转运体受葡萄糖通过己糖激酶依赖性途径的调节。
