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

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

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Department of Biosciences, Molecular Cell Biology of Plants, Center of Membrane Proteomics and Cluster of Excellence Frankfurt, Goethe University, Max-von-Laue Str 9, D-60438 Frankfurt, Germany.


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.


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

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