Gene expression in response to endoplasmic reticulum stress in Arabidopsis thaliana

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Abstract
Eukaryotic cells respond to the accumulation of unfolded proteins in the endoplasmic reticulum (ER). In this case, so‐called unfolded protein response (UPR) genes are induced. We determined the transcriptional expression of Arabidopsis thaliana UPR genes by fluid microarray analysis of tunicamycin‐treated plantlets. Two hundred and fifteen up‐regulated genes and 17 down‐regulated ones were identified. These genes were reanalyzed with functional DNA microarrays, using DNA fragments cloned through fluid microarray analysis. Finally, 36 up‐regulated and two down‐regulated genes were recognized as UPR genes. Among them, the up‐regulation of genes related to protein degradation (HRD1, SEL‐1L/HRD3 and DER1), regulation of translation (P58IPK), and apoptosis (BAX inhibitor‐1) was reconfirmed by real‐time reverse transcriptase‐PCR. The induction of SEL‐1L protein in an Arabidopsis membrane fraction on tunicamycin‐treatment was demonstrated. Phosphorylation of initiation factor‐2α, which was inhibited by P58IPK, was decreased in tunicamycin‐treated plantlets. However, regulatory changes in translation caused by ER stress were not detected in Arabidopsis. Plant cells appeared to have a strategy for overcoming ER stress through enhancement of protein folding activity, degradation of unfolded proteins, and regulation of apoptosis, but not regulation of translation.