title: Defects in IRE1 enhance cell death and fail to degrade mRNAs encoding secretory pathway proteins in the Arabidopsis unfolded protein response.
abstract: The unfolded protein response (UPR) is a cellular response highly conserved in eukaryotes to obviate accumulation of misfolded proteins in the endoplasmic reticulum (ER). Inositol-requiring enzyme 1 (IRE1) catalyzes the cytoplasmic splicing of mRNA encoding bZIP transcription factors to activate the UPR signaling pathway. Arabidopsis IRE1 was recently shown to be involved in the cytoplasmic splicing of bZIP60 mRNA. In the present study, we demonstrated that an Arabidopsis mutant with defects in two IRE1 paralogs showed enhanced cell death upon ER stress compared with a mutant with defects in bZIP60 and wild type, suggesting an alternative function of IRE1 in the UPR. Analysis of our previous microarray data and subsequent quantitative PCR indicated degradation of mRNAs encoding secretory pathway proteins by tunicamycin, DTT, and heat in an IRE1-dependent manner. The degradation of mRNAs localized to the ER during the UPR was considered analogous to a molecular mechanism referred to as the regulated IRE1-dependent decay of mRNAs reported in metazoans. Another microarray analysis conducted in the condition repressing transcription with actinomycin D and a subsequent Gene Set Enrichment Analysis revealed the regulated IRE1-dependent decay of mRNAs-mediated degradation of a significant portion of mRNAs encoding the secretory pathway proteins. In the mutant with defects in IRE1, genes involved in the cytosolic protein response such as heat shock factor A2 were up-regulated by tunicamycin, indicating the connection between the UPR and the cytosolic protein response.
authors.affiliation: Division of Applied Life Sciences, Graduate School of Life and Environmental Sciences, Osaka Prefecture University, Nakaku, Sakai, Osaka 599-8531, Japan.
authors.forename: Kei-ichiro
authors.initials: K
authors.lastname: Mishiba
authors.forename: Yukihiro
authors.initials: Y
authors.lastname: Nagashima
authors.forename: Eiji
authors.initials: E
authors.lastname: Suzuki
authors.forename: Noriko
authors.initials: N
authors.lastname: Hayashi
authors.forename: Yoshiyuki
authors.initials: Y
authors.lastname: Ogata
authors.forename: Yukihisa
authors.initials: Y
authors.lastname: Shimada
authors.forename: Nozomu
authors.initials: N
authors.lastname: Koizumi
mesh_terms: D017360:Arabidopsis / Q000235:genetics*; D029681:Arabidopsis Proteins / Q000235:genetics / Q000378:metabolism*; D050976:Basic-Leucine Zipper Transcription Factors / Q000235:genetics / Q000378:metabolism*; D019295:Computational Biology; D053938:DNA Fragmentation; D059865:Endoplasmic Reticulum Stress / Q000502:physiology*; D005070:Evans Blue; D018506:Gene Expression Regulation, Plant / Q000187:drug effects / Q000235:genetics*; D046228:Microarray Analysis; D009154:Mutation / Q000235:genetics; D011494:Protein Kinases / Q000235:genetics / Q000378:metabolism*; D020871:RNA Stability / Q000502:physiology; D014415:Tunicamycin / Q000494:pharmacology; D056811:Unfolded Protein Response / Q000235:genetics / Q000502:physiology*
chemical_list: D029681:Arabidopsis Proteins; D050976:Basic-Leucine Zipper Transcription Factors; D014415:Tunicamycin; D005070:Evans Blue; D011494:Protein Kinases; C446527:Ire1-1 protein, Arabidopsis