title: Evolutionary, molecular and genetic analyses of Tic22 homologues in Arabidopsis thaliana chloroplasts.
abstract: The Tic22 protein was previously identified in pea as a putative component of the chloroplast protein import apparatus. It is a peripheral protein of the inner envelope membrane, residing in the intermembrane space. In Arabidopsis, there are two Tic22 homologues, termed atTic22-III and atTic22-IV, both of which are predicted to localize in chloroplasts. These two proteins defined clades that are conserved in all land plants, which appear to have evolved at a similar rates since their separation >400 million years ago, suggesting functional conservation. The atTIC22-IV gene was expressed several-fold more highly than atTIC22-III, but the genes exhibited similar expression profiles and were expressed throughout development. Knockout mutants lacking atTic22-IV were visibly normal, whereas those lacking atTic22-III exhibited moderate chlorosis. Double mutants lacking both isoforms were more strongly chlorotic, particularly during early development, but were viable and fertile. Double-mutant chloroplasts were small and under-developed relative to those in wild type, and displayed inefficient import of precursor proteins. The data indicate that the two Tic22 isoforms act redundantly in chloroplast protein import, and that their function is non-essential but nonetheless required for normal chloroplast biogenesis, particularly during early plant development.
authors.affiliation: University of Leicester, Department of Biology, Leicester, United Kingdom.
authors.forename: Ali Reza
authors.initials: AR
authors.lastname: Kasmati
authors.forename: Mats
authors.initials: M
authors.lastname: Töpel
authors.forename: Nadir Zaman
authors.initials: NZ
authors.lastname: Khan
authors.forename: Ramesh
authors.initials: R
authors.lastname: Patel
authors.forename: Qihua
authors.initials: Q
authors.lastname: Ling
authors.forename: Sazzad
authors.initials: S
authors.lastname: Karim
authors.forename: Henrik
authors.initials: H
authors.lastname: Aronsson
authors.forename: Paul
authors.initials: P
authors.lastname: Jarvis
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D029681:Arabidopsis Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism / Q000648:ultrastructure; D019143:Evolution, Molecular; D018507:Gene Expression Regulation, Developmental; D018506:Gene Expression Regulation, Plant; D007425:Intracellular Membranes / Q000378:metabolism* / Q000648:ultrastructure; D026901:Membrane Transport Proteins / Q000145:classification / Q000235:genetics* / Q000378:metabolism; D009154:Mutation; D010641:Phenotype; D010802:Phylogeny; D020033:Protein Isoforms / Q000145:classification / Q000235:genetics / Q000378:metabolism
chemical_list: D029681:Arabidopsis Proteins; D026901:Membrane Transport Proteins; D020033:Protein Isoforms; C584696:Tic22 protein, Arabidopsis