Key Laboratory of Plant Resources, Institute of Botany, Chinese Academy of Sciences, Beijing 100093, China.
Plant Cell Physiol. 2013 Dec;54(12):2020-33. doi: 10.1093/pcp/pct142. Epub 2013 Oct 3.
Abiotic stresses disrupt protein folding and induce endoplasmic reticulum (ER) stress, which in turn activates the unfolded protein response (UPR) to aid in the refolding or degradation of misfolded proteins. The phytohormone ABA regulates many aspects of plant development and plays a central role in the stress response; however, the role of ABA in transducing stress signals to activate the UPR has not been recognized. In this study, a gene encoding the maize ortholog of AtbZIP17, a transmembrane transcription factor functioning as an ER stress transducer, was identified from the MaizeGDB database, and designated ZmbZIP17. ZmbZIP17 was induced by both ABA and ER stress-eliciting agents such as dithiotreitol (DTT) and tunicamycin (TM). Transiently expressed yellow fluorescent protein (YFP)-ZmbZIP17 co-localized with the ER marker HDEL-mCherry under control conditions, but partially translocated into the nucleus upon TM treatment or removal of the transmembrane domain. TM-induced processing of ZmbZIP17 was confirmed by Western blot analysis. When overexpressed in Arabidopsis, ZmbZIP17 triggered ER stress response gene expression and tolerance to DTT and TM, elevated ABA-responsive gene expression and ABA sensitivity both pre- and post-germination. Additionally, ABA was found to induce ER stress response gene expression, alone or synergistically with ZmbZIP17, in the absence of DTT or TM; while ZmbZIP17 was capable of interacting with ABA-responsive cis-elements (ABREs) that exist in promoters of known ABA-responsive genes. Together, our results reveal a direct link between ER stress and ABA signaling pathways involving the ZmbZIP17 transcription factor.
非生物胁迫会破坏蛋白质折叠，并诱导内质网（ER）应激，进而激活未折叠蛋白反应（UPR），以帮助错误折叠的蛋白质重折叠或降解。植物激素 ABA 调节植物发育的许多方面，在应激反应中起着核心作用；然而，ABA 在将应激信号转导到激活 UPR 中的作用尚未得到认可。在这项研究中，从 MaizeGDB 数据库中鉴定出一个编码玉米直系同源物 AtbZIP17 的基因，AtbZIP17 是一种跨膜转录因子，作为 ER 应激传感器发挥作用，并将其命名为 ZmbZIP17。ZmbZIP17 既被 ABA 诱导，也被 ER 应激诱导剂如二硫苏糖醇（DTT）和衣霉素（TM）诱导。在对照条件下，瞬时表达的黄色荧光蛋白（YFP）-ZmbZIP17 与 ER 标记物 HDEL-mCherry 共定位，但在 TM 处理或跨膜结构域去除后部分转移到核内。通过 Western blot 分析证实了 TM 诱导的 ZmbZIP17 加工。当在拟南芥中过表达时，ZmbZIP17 触发 ER 应激反应基因表达和对 DTT 和 TM 的耐受性，提高了 ABA 响应基因表达和发芽前后的 ABA 敏感性。此外，发现 ABA 单独或与 ZmbZIP17 协同诱导 ER 应激反应基因表达，而无需 DTT 或 TM；而 ZmbZIP17 能够与已知的 ABA 响应基因启动子中存在的 ABA 响应顺式元件（ABREs）相互作用。总之，我们的研究结果揭示了 ER 应激和涉及 ZmbZIP17 转录因子的 ABA 信号通路之间的直接联系。
