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Title: Molecular and genetic analyses of Tic20 homologues in Arabidopsis thaliana chloroplasts
Authors: Kasmati, Ali Reza
Töpel, Mats
Patel, Ramesh
Murtaza, Ghulam
Jarvis, Paul
First Published: 4-Apr-2011
Publisher: Blackwell Publishing in association with the Society for Experimental Biology
Citation: The Plant Journal, 2011, 66 (5), pp. 877-889.
Abstract: The Tic20 protein was identified in pea (Pisum sativum) as a component of the chloroplast protein import apparatus. In Arabidopsis, there are four Tic20 homologues, termed atTic20-I, atTic20-IV, atTic20-II and atTic20-V, all with predicted topological similarity to the pea protein (psTic20). Analysis of Tic20 sequences from many species indicated that they are phylogenetically unrelated to mitochondrial Tim17-22-23 proteins, and that they form two evolutionarily conserved subgroups [characterized by psTic20/atTic20-I/IV (Group 1) and atTic20-II/V (Group 2)]. Like psTic20, all four Arabidopsis proteins have a predicted transit peptide consistent with targeting to the inner envelope. Envelope localization of each one was confirmed by analysis of YFP fusions. RT-PCR and microarray data revealed that the four genes are expressed throughout development. To assess the functional significance of the genes, T-DNA mutants were identified. Homozygous tic20-I plants had an albino phenotype that correlated with abnormal chloroplast development and reduced levels of chloroplast proteins. However, knockouts for the other three genes were indistinguishable from the wild type. To test for redundancy, double and triple mutants were studied; apart from those involving tic20-I, none was distinguishable from the wild type. The tic20-I tic20-II and tic20-I tic20-V double mutants were albino, like the corresponding tic20-I parent. In contrast, tic20-I tic20-IV double homozygotes could not be identified, due to gametophytic and embryonic lethality. Redundancy between atTic20-I and atTic20-IV was confirmed by complementation analysis. Thus, atTic20-I and atTic20-IV are the major functional Tic20 isoforms in Arabidopsis, with partially overlapping roles. While the Group 2 proteins have been conserved over approximately 1.2 billion (1.2 × 109) years, they are not essential for normal development.
DOI Link: 10.1111/j.1365-313X.2011.04551.x
ISSN: 0960-7412
eISSN: 1365-313X
Version: Post print
Status: Peer reviewed
Type: Article
Rights: © 2011 The Authors. The Plant Journal © 2011 Blackwell Publishing Ltd. Deposited with reference to the publisher's archiving policy available from the journal Exclusive Licence Form, which permits posting of the accepted version of the Article as originally submitted for publication and updated to include any amendments made after peer review 12 months after publication. The definitive version is available at
Appears in Collections:Published Articles, Dept. of Biology

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