Constitutive BiP protein accumulation in Arabidopsis mutants defective in a gene encoding chloroplast-resident stearoyl-acyl carrier protein desaturase

Genes Cells. 2018 Jun;23(6):456-465. doi: 10.1111/gtc.12585. Epub 2018 Apr 24.


The unfolded protein response (UPR) occurs when protein folding and maturation are disturbed in the endoplasmic reticulum (ER). During the UPR, a number of genes including those encoding ER-resident molecular chaperones are induced. In Arabidopsis, BiP3 has been used as a UPR marker gene whose expression is strongly induced in response to ER stress. In this study, we mutagenized Arabidopsis plants expressing β-glucuronidase (GUS) gene under the control of BiP3 promoter and isolated a mutant that exhibits strong GUS activity without treatment with ER stress inducers. By whole genome sequencing, we identified a causal gene in the mutant as SUPPRESSOR OF SALICYLIC ACID INSENSITIVITY2 (SSI2), which encodes stearoyl-acyl carrier protein desaturase that converts stearic acids to oleic acids in the chloroplasts. In addition to GUS proteins, the ssi2 mutant accumulates endogenous BiP3 proteins without treatment by any stress reagents. Interestingly, although the degree of endogenous BiP3 protein accumulation in the ssi2 mutant was comparable to that in wild-type plants treated with the ER stress inducer tunicamycin, much less BiP3 transcripts were detected in the ssi2 mutant compared to tunicamycin-treated wild-type plants. Our finding suggests a genetic link between fatty acid metabolism in the chloroplasts and ER functions.

Keywords: Arabidopsis thaliana; binding protein; endoplasmic reticulum stress; fatty acid; stearoyl-acyl carrier protein desaturase; unfolded protein response.

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis / metabolism*
  • Arabidopsis Proteins / genetics*
  • Arabidopsis Proteins / metabolism*
  • Basic-Leucine Zipper Transcription Factors / genetics
  • Basic-Leucine Zipper Transcription Factors / metabolism
  • Chloroplasts / metabolism*
  • Endoplasmic Reticulum / metabolism
  • Fatty Acid Desaturases / genetics*
  • Fatty Acid Desaturases / metabolism
  • Fatty Acids / metabolism
  • Gene Expression Regulation, Plant*
  • Molecular Chaperones / genetics
  • Molecular Chaperones / metabolism*
  • Mutation*
  • Phenotype
  • Plants, Genetically Modified
  • Unfolded Protein Response


  • Arabidopsis Proteins
  • Basic-Leucine Zipper Transcription Factors
  • BiP3 protein, Arabidopsis
  • Fatty Acids
  • Molecular Chaperones
  • bZIP60 protein, Arabidopsis
  • Fatty Acid Desaturases
  • stearoyl ACP desaturase, Arabidopsis