Endoplasmic reticulum stress activates the expression of a sub-group of protein disulfide isomerase genes and AtbZIP60 modulates the response in Arabidopsis thaliana.

Proteins entering the secretory pathway of eukaryotic cells are folded into their native structures in the endoplasmic reticulum (ER). Disruption of protein folding causes ER stress and activates signaling cascades, designated the unfolded protein response (UPR), that restore folding capacity. In mammals and yeast, the protein disulfide isomerases (PDIs) are key protein folding catalysts activated during UPR. However, little is known about the response of PDI genes to UPR in plants. In Arabidopsis thaliana, we identified 12 PDI genes that differed in polypeptide length, presence of signal peptide and ER retention signal, and the number and positions of thioredoxin and transmembrane domains. AtPDI gene expression was investigated in different tissues, in response to chemically induced UPR, and in null mutants of UPR signaling mediators (AtIRE1-2 and AtbZIP60). The expression of six AtPDI genes was significantly up-regulated by UPR and sharply attenuated by the transcription inhibitor, actinomycin D, indicating UPR induced AtPDI gene transcription. AtPDI and BIP2 (Binding protein) gene expression was not affected in the Atire1-2 mutant exposed to UPR, however, the expression of four AtPDI genes was decreased in the Atbzip60 mutant. We proposed that additional UPR signaling factors complement AtbZIP60 in the activation of AtPDI gene expression during ER stress in plants.