In vivo function of Tic22, a protein import component of the intermembrane space of chloroplasts

Mol Plant. 2013 May;6(3):817-29. doi: 10.1093/mp/sss114. Epub 2012 Nov 30.


Preprotein import into chloroplasts depends on macromolecular machineries in the outer and inner chloroplast envelope membrane (TOC and TIC). It was suggested that both machineries are interconnected by components of the intermembrane space (IMS). That is, amongst others, Tic22, of which two closely related isoforms exist in Arabidopsis thaliana, namely atTic22-III and atTic22-IV. We investigated the function of Tic22 in vivo by analyzing T-DNA insertion lines of the corresponding genes. While the T-DNA insertion in the individual genes caused only slight defects, a double mutant of both isoforms showed retarded growth, a pale phenotype under high-light conditions, a reduced import rate, and a reduction in the photosynthetic performance of the plants. The latter is supported by changes in the metabolite content of mutant plants when compared to wild-type. Thus, our results support the notion that Tic22 is directly involved in chloroplast preprotein import and might point to a particular importance of Tic22 in chloroplast biogenesis at times of high import rates.

Keywords: TOC and TIC; chloroplast biogenesis; intermembrane space translocon; metabolite content; protein translocation.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Arabidopsis / genetics
  • Arabidopsis / growth & development
  • Arabidopsis / metabolism*
  • Arabidopsis / radiation effects
  • Arabidopsis Proteins / genetics
  • Arabidopsis Proteins / metabolism*
  • Chlorophyll / metabolism
  • Chloroplasts / metabolism*
  • Chloroplasts / radiation effects
  • Chloroplasts / ultrastructure
  • DNA, Bacterial / genetics
  • Gene Deletion
  • Gene Expression Profiling
  • Gene Expression Regulation, Plant / radiation effects
  • Gene Knockout Techniques
  • Genes, Plant / genetics
  • Genotype
  • Intracellular Membranes / metabolism*
  • Intracellular Membranes / radiation effects
  • Intracellular Membranes / ultrastructure
  • Light
  • Membrane Transport Proteins / genetics
  • Membrane Transport Proteins / metabolism*
  • Metabolome / radiation effects
  • Mutagenesis, Insertional / genetics
  • Phenotype
  • Photosynthesis / radiation effects
  • Plant Development / genetics
  • Plant Development / radiation effects
  • Protein Transport / radiation effects


  • Arabidopsis Proteins
  • DNA, Bacterial
  • Membrane Transport Proteins
  • T-DNA
  • Tic22 protein, Arabidopsis
  • Chlorophyll