The basic leucine zipper (bZIP) transcription factors (TFs) function as regulators of many key developmental and physiological processes in all eukaryotes. In this study, we characterized the function of Arabidopsis bZIP4, a group S bZIP, whose function was not known. We confirmed that bZIP4 localizes to the nucleus and has DNA-binding affinity. By qRT-PCR and GUS histochemical analysis, we showed that bZIP4 is specifically expressed in root and that its expression is induced by abiotic stress and ABA. By phenotypic analysis, we demonstrated that the root length and the germination rate of bZIP4 overexpression (bZIP4-Ox) were significantly longer and higher than those of the WT and bZIP4-SRDX under higher salt and glucose concentrations, indicating that bZIP4-Ox is insensitive and tolerant to abiotic stress. Despite that, we found that bZIP4-Ox had enhanced expression of genes encoding protein phosphatases suppressing ABA responsiveness. We also confirmed that bZIP4 interacts with CaM1 and showed that its DNA-binding affinity is inhibited by interaction with CaM1. We propose a model in which the increased cytosolic calcium concentration under stress conditions activates CaM1 to bind bZIP4 to remove it from promoters of genes encoding ABA negative regulators, allowing the plants to operate on a typical ABA signaling pathway.

基本的亮氨酸拉链（bZIP）转录因子（TF）充当所有真核生物中许多关键发育和生理过程的调节剂。在这项研究中，我们表征了其功能未知的拟南芥bZIP4（S组bZIP）的功能。我们证实，bZIP4定位于细胞核，并具有DNA结合亲和力。通过qRT-PCR和GUS组织化学分析，我们表明bZIP4在根中特异性表达，并且其表达是由非生物胁迫和ABA诱导的。通过表型分析，我们证明了bZIP4过表达（bZIP4 -Ox）的根长和发芽率明显长于WT和bZIP4的根长和发芽率。-SRDX在较高的盐和葡萄糖浓度下，表明bZIP4- Ox对非生物胁迫不敏感且耐受。尽管如此，我们发现bZIP4- Ox增强了编码抑制ABA反应的蛋白磷酸酶的基因的表达。我们还证实了bZIP4与CaM1相互作用，并表明与CaM1相互作用抑制了其DNA结合亲和力。我们提出了一个模型，其中在胁迫条件下增加的胞质钙浓度激活CaM1以结合bZIP4，以将其从编码ABA负调控子的基因启动子中删除，从而使植物能够在典型的ABA信号转导途径上运行。