The tobacco bZIP transcription factor BZI-1 binds to G-box elements in the promoters of phenylpropanoid pathway genes in vitro, but it is not involved in their regulation in vivo
The tobacco bZIP transcription factor BZI-1 binds to G-box elements in the promoters of phenylpropanoid pathway genes in vitro, but it is not involved in their regulation in vivo
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DOI：
10.1007/s00438-001-0636-3
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发表时间：
2002-03-01
影响因子：
3.1
通讯作者：
Dröge-Laser, W
中科院分区：
文献类型：
--
作者：
Heinekamp, T;Kuhlmann, M;Dröge-Laser, W
对烟草 (Nicotiana tabacum) cDNA 文库的筛选导致分离出编码 bZIP 转录因子 BZI-1 的克隆。在氨基酸序列、蛋白结构域保守性、基因组外显子-内含子结构和表达模式方面，BZI-1与CPRF2、OHP1/2密切相关。 BLZ1 和 REB 是一组 bZIP 蛋白，已在许多双子叶植物和单子叶植物物种中得到描述。 BZI-1表现出转录因子的特征。它在体外与 G 盒和 C 盒顺式元件结合，位于细胞核中，BZI-1 的 N 末端区域在酵母和植物细胞中充当激活结构域。由于 BZI-1 相关转录因子已通过体外结合查尔酮合酶 (CHS) 启动子中的 G-box 元件从双子叶植物中分离出来，因此有人认为苯丙素途径基因，如 CHS 和 PAL（苯丙氨酸解氨酶）是体内这些蛋白质的靶标。然而，在感染丁香假单胞菌或烟草花叶病毒后，在表达 BZI-1 或显性失活形式的蛋白质 BZI-1-DeltaN 水平增加的转基因植物中，没有观察到病原体诱导的 PAL 表达发生变化。与 CHS 和 PAL 的组织特异性表达相反，BZI-1 被发现在烟草植物中普遍表达。此外，在 BZI-1-DeltaN 转基因植物中没有观察到 PAL 或 CHS 的组织特异性表达发生变化。 VP16-BZI-1 融合蛋白的表达预计会导致 BZI-1 靶基因的组成型激活。然而，烟草植物中 VP16-BZI-1 蛋白的四环素依赖性表达不会导致 CHS 或 PAL 的激活。根据这些数据，我们得出结论，所分析的苯丙素途径基因不是 BZI-1 体内的靶标。因此，转录因子的体外 DNA 结合模式并不总是反映它们的体内功能。
Screening of a tobacco (Nicotiana tabacum) cDNA library resulted in the isolation of a clone encoding the bZIP transcription factor BZI-1. With respect to amino acid sequence, conservation of protein domains, genomic exon-intron structure and expression pattern, BZI-1 is closely related to CPRF2, OHP1/2. BLZ1 and REB, a group of bZIP proteins which have been described in a number of dicot and monocot species. BZI-1 exhibits the characteristics of a transcription factor. It binds to G-box and C-box cis-elements in vitro, it is localised in the nucleus, and the N-terminal region of BZI-1 functions as an activation domain in both yeast and plant cells. Since BZI-1-related transcription factors have been isolated from dicots by in vitro binding to G-box elements in the chalcone synthase (CHS) promoter, it has been suggested that phenylpropanoid pathway genes, such as CHS and PAL (phenylalanine ammonia-lyase), are targets of these proteins in vivo. However, after infection with Pseudomonas syringae or Tobacco Mosaic Virus, no changes in pathogen-induced PAL expression were observed in transgenic plants expressing increased levels of BZI-1 or a dominant negative form of the protein, BZI-1-DeltaN. In contrast to the tissue-specific expression of CHS and PAL, BZI-1 was found to be ubiquitously expressed in tobacco plants. Furthermore, no changes in the tissue-specific expression of PAL or CHS were observed in plants that were transgenic for BZI-1-DeltaN. Expression of a VP16-BZI-1 fusion protein would be expected to result in constitutive activation of the BZI-1 target genes. However, tetracycline-dependent expression of a VP16-BZI-1 protein in tobacco plants did not result in activation of CHS or PAL. On the basis of these data, we conclude that the phenylpropanoid pathway genes analysed are not targets of BZI-1 in vivo. Thus, the pattern of in vitro DNA binding of transcription factors need not always reflect their in vivo function.