title: Molecular characterization and expression analysis of chloroplast protein import components in tomato (Solanum lycopersicum).
abstract: The translocon at the outer envelope membrane of chloroplasts (Toc) mediates the recognition and initial import into the organelle of thousands of nucleus-encoded proteins. These proteins are translated in the cytosol as precursor proteins with cleavable amino-terminal targeting sequences called transit peptides. The majority of the known Toc components that mediate chloroplast protein import were originally identified in pea, and more recently have been studied most extensively in Arabidopsis. With the completion of the tomato genome sequencing project, it is now possible to identify putative homologues of the chloroplast import components in tomato. In the work reported here, the Toc GTPase cDNAs from tomato were identified, cloned and analyzed. The analysis revealed that there are four Toc159 homologues (slToc159-1, -2, -3 and -4) and two Toc34 homologues (slToc34-1 and -2) in tomato, and it was shown that tomato Toc159 and Toc34 homologues share high sequence similarity with the comparable import apparatus components from Arabidopsis and pea. Thus, tomato is a valid model for further study of this system. The expression level of Toc complex components was also investigated in different tissues during tomato development. The two tomato Toc34 homologues are expressed at higher levels in non-photosynthetic tissues, whereas, the expression of two tomato Toc159 homologues, slToc159-1 and slToc159-4, were higher in photosynthetic tissues, and the expression patterns of slToc159-2 was not significantly different in photosynthetic and non-photosynthetic tissues, and slToc159-3 expression was limited to a few select tissues.
authors.affiliation: College of Horticulture, Northwest A&F University, Yangling, Shaanxi, P.R. China; Department of Biology, University of Waterloo, Waterloo, Ontario, Canada.
authors.forename: Jianmin
authors.initials: J
authors.lastname: Yan
authors.affiliation: Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada.
authors.forename: James H
authors.initials: JH
authors.lastname: Campbell
authors.affiliation: Department of Biology, University of Waterloo, Waterloo, Ontario, Canada.
authors.forename: Bernard R
authors.initials: BR
authors.lastname: Glick
authors.affiliation: Department of Biology, Wilfrid Laurier University, Waterloo, Ontario, Canada.
authors.forename: Matthew D
authors.initials: MD
authors.lastname: Smith
authors.affiliation: College of Horticulture, Northwest A&F University, Yangling, Shaanxi, P.R. China.
authors.forename: Yan
authors.initials: Y
authors.lastname: Liang
mesh_terms: D000595:Amino Acid Sequence; D002736:Chloroplasts / Q000378:metabolism*; D032461:Chromosomes, Plant / Q000235:genetics; D003001:Cloning, Molecular; D017124:Conserved Sequence; D018076:DNA, Complementary / Q000235:genetics; D005091:Exons / Q000235:genetics; D020558:GTP Phosphohydrolases / Q000378:metabolism; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017343:Genes, Plant; D007438:Introns / Q000235:genetics; D018551:Solanum lycopersicum / Q000235:genetics* / Q000378:metabolism*; D008969:Molecular Sequence Data; D009928:Organ Specificity / Q000235:genetics; D010802:Phylogeny; D010940:Plant Proteins / Q000737:chemistry / Q000235:genetics* / Q000378:metabolism; D017434:Protein Structure, Tertiary; D021381:Protein Transport; D020539:Sequence Analysis, Protein; D040681:Structural Homology, Protein
chemical_list: D018076:DNA, Complementary; D010940:Plant Proteins; D020558:GTP Phosphohydrolases
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