Arabidopsis tRNA ligase completes the cytoplasmic splicing of bZIP60 mRNA in the unfolded protein response

Biochem Biophys Res Commun. 2016 Feb 19;470(4):941-6. doi: 10.1016/j.bbrc.2016.01.145. Epub 2016 Jan 26.


Arabidopsis bZIP60 is a major transcription factor that activates the unfolded protein response and is regulated by cytoplasmic splicing. Two Arabidopsis inositol-requiring 1s (IRE1A and IRE1B) cleave bZIP60 mRNA; however, the ligase that connects the two half-molecules of the split bZIP60 mRNA has not yet been identified. We aimed to determine whether the Arabidopsis tRNA ligase RLG1 catalyzes the ligation of cleaved bZIP60 mRNA. Recombinant IRE1B containing the ribonuclease domain correctly cleaved synthetic RNA covering the cleaved site of bZIP60 in vitro. Recombinant RLG1 then ligated the two cleaved fragments. The cytoplasmic form of RLG1 was expressed in a T-DNA insertion mutant whose homozygote exhibited a lethal phenotype and when the transgene was substituted with endogenous RLG1, the plants grew normally. RLG1 proteins derived from transgene were mainly found in the cytoplasm; however, some were in the microsomal fraction, possibly on the ER membrane. This intracellular distribution of RLG1 is discussed.

Keywords: Arabidopsis; Cytoplasmic splicing; Transcription factor; Unfolded protein response; tRNA ligase.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / physiology*
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Basic-Leucine Zipper Transcription Factors / genetics
  • Basic-Leucine Zipper Transcription Factors / metabolism*
  • Cytoplasm / metabolism
  • Endoplasmic Reticulum / genetics
  • Endoplasmic Reticulum / metabolism*
  • RNA Ligase (ATP) / metabolism*
  • RNA Splicing / physiology*
  • Unfolded Protein Response / physiology*


  • Arabidopsis Proteins
  • Basic-Leucine Zipper Transcription Factors
  • bZIP60 protein, Arabidopsis
  • RNA Ligase (ATP)