Satoh Rie, Fujita Yasunari, Nakashima Kazuo, Shinozaki Kazuo, Yamaguchi-Shinozaki Kazuko
Biological Resources Division, Japan International Research Center for Agricultural Sciences, 1-1 Ohwashi, Tsukuba, Ibaraki, 305-8686 Japan.
Plant Cell Physiol. 2004 Mar;45(3):309-17. doi: 10.1093/pcp/pch036.
A 6-bp sequence, ACTCAT, acts as a cis-acting element involved in hypoosmolarity- and proline-responsive expression of an Arabidopsis proline dehydrogenase (ProDH) gene. Search of the database for plant cis-acting elements revealed that the ACTCAT sequence is similar to the GCN4 motif [ATGA(C/G)TCAT] that is recognized by bZIP transcription factors. To identify transcription factor(s) for regulation of ProDH, we examined whether Arabidopsis bZIPs function as transcription factors for the ACTCAT sequence. Transient expression analysis revealed that the four proteins in Group S bZIPs, AtbZIP11/ATB2, AtbZIP44, AtbZIP2/GBF5 and AtbZIP53, formed an ATB2 subgroup that activated expression of the GUS reporter gene driven by the ACTCAT sequence while other bZIPs and different families of plant transcription factors did not. The transactivation activity of the ATB2 subgroup was enhanced in a hypoosmotic condition. In a gel mobility shift assay, the recombinant proteins of the ATB2 subgroup specifically bound to the ACTCAT sequence. RNA gel blot analysis indicated that the expression of AtbZIP2/GBF5 and AtbZIP53, as well as that of ProDH, is induced by hypoosmolarity. Moreover, we showed that the sGFP::AtbZIP11/ATB2 fusion protein is localized in the nucleus. These results suggest that the ATB2 subgroup functions as a transcriptional activator for hypoosmolarity-inducible ProDH in Arabidopsis:
一段6个碱基对的序列ACTCAT，作为一个顺式作用元件，参与拟南芥脯氨酸脱氢酶（ProDH）基因的低渗和脯氨酸应答表达。在植物顺式作用元件数据库中搜索发现，ACTCAT序列与bZIP转录因子识别的GCN4基序[ATGA(C/G)TCAT]相似。为了鉴定调控ProDH的转录因子，我们检测了拟南芥bZIPs是否作为ACTCAT序列的转录因子发挥作用。瞬时表达分析表明，S组bZIPs中的四种蛋白AtbZIP11/ATB2、AtbZIP44、AtbZIP2/GBF5和AtbZIP53形成了一个ATB2亚组，该亚组激活了由ACTCAT序列驱动的GUS报告基因的表达，而其他bZIPs和不同家族的植物转录因子则没有。ATB2亚组的反式激活活性在低渗条件下增强。在凝胶迁移率变动分析中，ATB2亚组的重组蛋白特异性结合ACTCAT序列。RNA凝胶印迹分析表明，AtbZIP2/GBF5和AtbZIP53以及ProDH的表达受低渗诱导。此外，我们还表明sGFP::AtbZIP11/ATB2融合蛋白定位于细胞核。这些结果表明，ATB2亚组在拟南芥中作为低渗诱导的ProDH的转录激活因子发挥作用。
