Abstract
Proteins synthesized in the endoplasmic reticulum (ER) are correctly folded before translocation. If protein folding is incorrect, genes for the ER-resident chaperones such as BiP are induced. This phenomenon is known as the ER stress response. Studying molecular mechanism of the ER stress response in Arabidopsis, we identified a bZIP transcription factor AtbZIP60 induced by tunicamycin treatment. AtbZIP60 has a putative transmembrane domain in its C-terminal region. A truncated form without C-terminal region (AtbZIP60ΔC) fused with GFP localized to the nucleus. In addition, overexpression of AtbZIP60ΔC activated BiP promoters in a transient assay although full length did not, suggesting proteolysis triggers activation of the transcription activity. In a T-DNA tagged mutant of AtbZIP60, induction of one BiP gene was repressed. These results indicated that AtbZIP60 regulates the ER stress response in a manner specific to plants.
