ER-Anchored Transcription Factors bZIP17 and bZIP28 Regulate Root Elongation

The unfolded protein response (UPR; 未折叠蛋白反应) is a eukaryotic transcriptional regulatory network in response to accumulated malformed (畸形的) proteins in the endoplasmic reticulum (ER; 内质网). In Arabidopsis thaliana, three bZIP transcription factors are dedicated to (致力于) modulate the UPR: bZIP17, bZIP28, and bZIP60. Compared to bZIP28 and bZIP60 that have been relatively well studied, the physiological and transcriptional roles of bZIP17 remain largely unknown. In this report, we introduce a double knockout mutant of bZIP17 and bZIP28 to analyze the function of bZIP17. The mutant plant exhibited multiple developmental defects including scarce (缺乏的) root elongation and constantly over-induced bZIP60 activity, indicating the essential roles of bZIP17 and bZIP28 in plant development and UPR modulation. Extended analysis on the transcriptome of the three double knockout mutants of bZIP17, bZIP28, and bZIP60 genes revealed that bZIP28 and bZIP60 majorly activated the canonical UPR in response to stimuli. In contrast, bZIP17 conferred the non-inducible expression of multiple genes involved in cell growth together with bZIP28, particularly to sustain (维持) their expression under stressed conditions. Our study revealed the pivotal (关键的) roles of bZIP17 on plant UPR and vegetative development in functional redundancy with bZIP28.

未折叠蛋白反应是真核生物响应于内质网上过量畸形蛋白积累的转录调控网络。在拟南芥中，已经鉴定了bZIP17、bZIP28和bZIP2860这3个bZIP转录因子调控UPR。相比于已经研究得非常透彻的bZIP28和bZIP60，bZIP17在生理和转录上的研究还很少。本文利用bZIP17和bZIP28的双突变体来研究bZIP17的功能。突变体植株存在多个发育缺陷，包括根伸长缺陷和bZIP60活性的不断过量诱导，显示bZIP17和bZIP28在植物发育和UPR调控中起到了非常重要的作用。进一步关于bZIP17、bZIP28和bZIP60基因的三突变体转录分析显示bZIP28和bZIP60是响应刺激激活UPR的主要因子。相反，bZIP17会和bZIP28一起赋予参与细胞生长的多个基因的非诱导性表达，尤其是维持这些基因在胁迫条件下的稳定表达。本文的研究揭示了bZIP17在植物UPR和营养器官发育中的关键作用，该基因与bZIP28存在功能冗余。

通讯：Kazuo Shinozaki (http://www.csrs.riken.jp/en/labs/gdrg/)

个人简介：名古屋大学博士。

doi: https://doi.org/10.1104/pp.17.01414