title: The exception proves the rule? Dual targeting of nuclear-encoded proteins into endosymbiotic organelles.
abstract: Plant cells harbor two types of endosymbiotic organelle: mitochondria and chloroplasts. As a consequence of endosymbiotic gene transfer, the majority of their proteins are encoded in the nucleus and post-translationally 're'-imported into the respective target organelle. The corresponding transport signals are usually selective for a single organelle, but several proteins are transported into both the mitochondria and chloroplasts. To estimate the number of proteins with such dual targeting properties in Arabidopsis, we classified the proteins encoded by nuclear genes of endosymbiotic origin according to the respective targeting specificity of their N-terminal transport signals as predicted by the TargetP software package. Selected examples of the resulting protein classes were subsequently analyzed by transient transformation assays as well as by in organello protein transport experiments. It was found that most proteins with high prediction values for both organelles show dual targeting with both experimental approaches. Unexpectedly, however, dual targeting was even found among those proteins that are predicted to be localized solely in one of the two endosymbiotic organelles. In total, among the 16 candidate proteins analyzed, we identified 10 proteins with dual targeting properties. This unexpectedly high proportion suggests that such transport properties are much more abundant than anticipated.
authors.affiliation: Institute of Biology - Plant Physiology, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany.
authors.forename: Bianca
authors.initials: B
authors.lastname: Baudisch
authors.affiliation: Institute of Biology - Plant Physiology, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany.
authors.forename: Uwe
authors.initials: U
authors.lastname: Langner
authors.affiliation: Institute of Biology - Plant Physiology, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany.
authors.forename: Ingo
authors.initials: I
authors.lastname: Garz
authors.affiliation: Institute of Biology - Plant Physiology, Martin Luther University Halle-Wittenberg, Weinbergweg 10, 06120, Halle (Saale), Germany.
authors.forename: Ralf Bernd
authors.initials: RB
authors.lastname: Klösgen
mesh_terms: D017360:Arabidopsis / Q000235:genetics* / Q000378:metabolism; D029681:Arabidopsis Proteins / Q000235:genetics* / Q000378:metabolism; D001692:Biological Transport; D002467:Cell Nucleus / Q000235:genetics / Q000378:metabolism; D060365:Chloroplast Proteins / Q000235:genetics* / Q000378:metabolism; D002736:Chloroplasts / Q000235:genetics* / Q000378:metabolism; D008928:Mitochondria / Q000235:genetics* / Q000378:metabolism; D024101:Mitochondrial Proteins / Q000235:genetics* / Q000378:metabolism; D009687:Nuclear Proteins / Q000235:genetics* / Q000378:metabolism; D021381:Protein Transport; D011993:Recombinant Fusion Proteins; D015398:Signal Transduction; D012984:Software; D013559:Symbiosis
chemical_list: D029681:Arabidopsis Proteins; D060365:Chloroplast Proteins; D024101:Mitochondrial Proteins; D009687:Nuclear Proteins; D011993:Recombinant Fusion Proteins
keywords: chloroplasts; dual targeting; mitochondria; nuclear-encoded proteins; protein transport; transit peptide
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