IRE1/bZIP60-Mediated Unfolded Protein Response Plays Distinct Roles in Plant Immunity and Abiotic Stress Responses

Endoplasmic reticulum (ER)-mediated protein secretion and quality control have been shown to play an important role in immune responses in both animals and plants. In mammals, the ER membrane-located IRE1 kinase/endoribonuclease, a key regulator of unfolded protein response (UPR), is required for plasma cell development to accommodate massive secretion of immunoglobulins. Plant cells can secrete the so-called pathogenesis-related (PR) proteins with antimicrobial activities upon pathogen challenge. However, whether IRE1 plays any role in plant immunity is not known. Arabidopsis thaliana has two copies of IRE1, IRE1a and IRE1b. Here, we show that both IRE1a and IRE1b are transcriptionally induced during chemically-induced ER stress, bacterial pathogen infection and treatment with the immune signal salicylic acid (SA). However, we found that IRE1a plays a predominant role in the secretion of PR proteins upon SA treatment. Consequently, the ire1a mutant plants show enhanced susceptibility to a bacterial pathogen and are deficient in establishing systemic acquired resistance (SAR), whereas ire1b is unaffected in these responses. We further demonstrate that the immune deficiency in ire1a is due to a defect in SA- and pathogen-triggered, IRE1-mediated cytoplasmic splicing of the bZIP60 mRNA, which encodes a transcription factor involved in the expression of UPR-responsive genes. Consistently, IRE1a is preferentially required for bZIP60 splicing upon pathogen infection, while IRE1b plays a major role in bZIP60 processing upon Tunicamycin (Tm)-induced stress. We also show that SA-dependent induction of UPR-responsive genes is altered in the bzip60 mutant resulting in a moderate susceptibility to a bacterial pathogen. These results indicate that the IRE1/bZIP60 branch of UPR is a part of the plant response to pathogens for which the two Arabidopsis IRE1 isoforms play only partially overlapping roles and that IRE1 has both bZIP60-dependent and bZIP60-independent functions in plant immunity.

[1]  Chao Zhang,et al.  The unfolded protein response signals through high-order assembly of Ire1 , 2009, Nature.

[2]  N. Koizumi,et al.  An Arabidopsis transcription factor, AtbZIP60, regulates the endoplasmic reticulum stress response in a manner unique to plants. , 2005, Proceedings of the National Academy of Sciences of the United States of America.

[3]  M. S. Mukhtar,et al.  NPR1 in Plant Defense: It's Not over 'til It's Turned over , 2009, Cell.

[4]  H. Yoshida.  Unconventional splicing of XBP-1 mRNA in the unfolded protein response. , 2007, Antioxidants & redox signaling.

[5]  P. Walter,et al.  Oligomerization and phosphorylation of the Ire1p kinase during intracellular signaling from the endoplasmic reticulum to the nucleus. , 1996, The EMBO journal.

[6]  Kathryn L. Lipson,et al.  Regulation of insulin biosynthesis in pancreatic beta cells by an endoplasmic reticulum-resident protein kinase IRE1. , 2006, Cell metabolism.

[7]  F. Martinon,et al.  Regulation of innate immunity by signaling pathways emerging from the endoplasmic reticulum. , 2011, Current opinion in immunology.

[8]  Y. Kimata,et al.  Molecular characterization of two Arabidopsis Ire1 homologs, endoplasmic reticulum-located transmembrane protein kinases. , 2001, Plant physiology.

[9]  S. Clough,et al.  Floral dip: a simplified method for Agrobacterium-mediated transformation of Arabidopsis thaliana. , 1998, The Plant journal : for cell and molecular biology.

[10]  D. Pincus,et al.  BiP Binding to the ER-Stress Sensor Ire1 Tunes the Homeostatic Behavior of the Unfolded Protein Response , 2010, PLoS biology.

[11]  Jonathan S Weissman,et al.  Decay of Endoplasmic Reticulum-Localized mRNAs During the Unfolded Protein Response , 2006, Science.

[12]  M. S. Mukhtar,et al.  Independently Evolved Virulence Effectors Converge onto Hubs in a Plant Immune System Network , 2011, Science.

[13]  P. Hummelen,et al.  Early genomic responses to salicylic acid in Arabidopsis , 2009, Plant Molecular Biology.

[14]  N. Amornsiripanitch,et al.  A Genomic Approach to Identify Regulatory Nodes in the Transcriptional Network of Systemic Acquired Resistance in Plants , 2006, PLoS pathogens.

[15]  R. Kaufman,et al.  The endoribonuclease activity of mammalian IRE1 autoregulates its mRNA and is required for the unfolded protein response. , 2000, Genes & development.

[16]  P. Walter,et al.  Signal integration in the endoplasmic reticulum unfolded protein response , 2007, Nature Reviews Molecular Cell Biology.

[17]  D. Christopher,et al.  Endoplasmic reticulum stress activates the expression of a sub-group of protein disulfide isomerase genes and AtbZIP60 modulates the response in Arabidopsis thaliana , 2008, Molecular Genetics and Genomics.

[18]  Y. Kimata,et al.  Endoplasmic reticulum stress-sensing mechanisms in yeast and mammalian cells. , 2011, Current opinion in cell biology.

[19]  Jane Glazebrook,et al.  The Arabidopsis NPR1 Gene That Controls Systemic Acquired Resistance Encodes a Novel Protein Containing Ankyrin Repeats , 1997, Cell.

[20]  H. Matsumura,et al.  Spermine signaling plays a significant role in the defense response of Arabidopsis thaliana to cucumber mosaic virus. , 2009, Journal of plant physiology.

[21]  C. Kwon,et al.  Characterization of two homologs of Ire1p, a kinase/endoribonuclease in yeast, in Arabidopsis thaliana. , 2002, Biochimica et biophysica acta.

[22]  K. Mishiba,et al.  Arabidopsis IRE1 catalyses unconventional splicing of bZIP60 mRNA to produce the active transcription factor , 2011, Scientific reports.

[23]  Jonathan D. G. Jones,et al.  The plant immune system , 2006, Nature.

[24]  P. Zimmermann,et al.  GENEVESTIGATOR. Arabidopsis Microarray Database and Analysis Toolbox1[w] , 2004, Plant Physiology.

[25]  Shui Wang,et al.  Arabidopsis SNI1 and RAD51D regulate both gene transcription and DNA recombination during the defense response , 2007, Proceedings of the National Academy of Sciences.

[26]  S. Howell,et al.  An Endoplasmic Reticulum Stress Response in Arabidopsis Is Mediated by Proteolytic Processing and Nuclear Relocation of a Membrane-Associated Transcription Factor, bZIP28[W][OA] , 2007, The Plant Cell Online.

[27]  P. Walter,et al.  Intracellular signaling from the endoplasmic reticulum to the nucleus: the unfolded protein response in yeast and mammals. , 2001, Current opinion in cell biology.

[28]  Xinnian Dong,et al.  Characterization of an Arabidopsis Mutant That Is Nonresponsive to Inducers of Systemic Acquired Resistance. , 1994, The Plant cell.

[29]  S. Aiba,et al.  Quantitative measurement of spliced XBP1 mRNA as an indicator of endoplasmic reticulum stress. , 2006, The Journal of toxicological sciences.

[30]  M. Yuan,et al.  The unfolded protein response induced by salt stress in Arabidopsis. , 2011, Methods in enzymology.

[31]  S. Howell,et al.  Salt stress responses in Arabidopsis utilize a signal transduction pathway related to endoplasmic reticulum stress signaling , 2007, The Plant journal : for cell and molecular biology.

[32]  R. Kaufman,et al.  Inositol-requiring 1/X-box-binding protein 1 is a regulatory hub that links endoplasmic reticulum homeostasis with innate immunity and metabolism , 2010, EMBO molecular medicine.

[33]  Judy H. Cho,et al.  Increased sensitivity to dextran sodium sulfate colitis in IRE1beta-deficient mice. , 2001, The Journal of clinical investigation.

[34]  Y. Nakamura,et al.  Monitoring of methyl jasmonate-responsive genes in Arabidopsis by cDNA macroarray: self-activation of jasmonic acid biosynthesis and crosstalk with other phytohormone signaling pathways. , 2001, DNA research : an international journal for rapid publication of reports on genes and genomes.

[35]  C. Benning,et al.  A membrane-tethered transcription factor defines a branch of the heat stress response in Arabidopsis thaliana , 2008, Proceedings of the National Academy of Sciences.

[36]  Karolina M. Pajerowska-Mukhtar,et al.  The HSF-like Transcription Factor TBF1 Is a Major Molecular Switch for Plant Growth-to-Defense Transition , 2012, Current Biology.

[37]  Jeffery L Dangl,et al.  Arabidopsis and the plant immune system. , 2010, The Plant journal : for cell and molecular biology.

[38]  S. Rothstein,et al.  Heat induces the splicing by IRE1 of a mRNA encoding a transcription factor involved in the unfolded protein response in Arabidopsis , 2011, Proceedings of the National Academy of Sciences.

[39]  Neal N. Iwakoshi,et al.  Plasma cell differentiation requires the transcription factor XBP-1 , 2001, Nature.

[40]  Anne Bertolotti,et al.  Dynamic interaction of BiP and ER stress transducers in the unfolded-protein response , 2000, Nature Cell Biology.

[41]  N. Koizumi,et al.  NtbZIP60, an endoplasmic reticulum-localized transcription factor, plays a role in the defense response against bacterial pathogens in Nicotiana tabacum , 2008, Journal of Plant Research.

[42]  Uwe Conrath,et al.  Systemic Acquired Resistance , 2006, Plant signaling & behavior.

[43]  J. Latgé,et al.  HacA-Independent Functions of the ER Stress Sensor IreA Synergize with the Canonical UPR to Influence Virulence Traits in Aspergillus fumigatus , 2011, PLoS pathogens.

[44]  S. Spoel,et al.  Making sense of hormone crosstalk during plant immune responses. , 2008, Cell host & microbe.

[45]  R. Kaufman,et al.  A stress response pathway from the endoplasmic reticulum to the nucleus requires a novel bifunctional protein kinase/endoribonuclease (Ire1p) in mammalian cells. , 1998, Genes & development.

[46]  M. Dickman,et al.  The Unfolded Protein Response Is Triggered by a Plant Viral Movement Protein1[W][OA] , 2011, Plant Physiology.

[47]  R. Kaufman,et al.  The mammalian unfolded protein response. , 2003, Annual review of biochemistry.

[48]  T. Iwawaki,et al.  Translational control by the ER transmembrane kinase/ribonuclease IRE1 under ER stress , 2001, Nature Cell Biology.

[49]  K. Shinozaki,et al.  Identification of stress-tolerance-related transcription-factor genes via mini-scale Full-length cDNA Over-eXpressor (FOX) gene hunting system. , 2007, Biochemical and biophysical research communications.

[50]  K. Rajewsky,et al.  Plasma cell differentiation and the unfolded protein response intersect at the transcription factor XBP-1 , 2003, Nature Immunology.

[51]  M. Yuan,et al.  The putative Arabidopsis zinc transporter ZTP29 is involved in the response to salt stress , 2010, Plant Molecular Biology.

[52]  T. Kooistra,et al.  An Essential Role for XBP-1 in Host Protection against Immune Activation in C. elegans , 2010, Nature.

[53]  M. Lehrman,et al.  Discordance of UPR signaling by ATF6 and Ire1p-XBP1 with levels of target transcripts. , 2004, Biochemical and biophysical research communications.

[54]  Dong Wang,et al.  Induction of Protein Secretory Pathway Is Required for Systemic Acquired Resistance , 2005, Science.

[55]  Varsha Singh,et al.  Neuronal GPCR Controls Innate Immunity by Regulating Noncanonical Unfolded Protein Response Genes , 2011, Science.

[56]  N. Koizumi,et al.  Transcriptomic response of Arabidopsis thaliana to tunicamycin-induced endoplasmic reticulum stress , 2010 .