RNA Edierung als molekulare Ursache für Kerngenom-Plastom-Inkompatibilität
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Philipps-Universität Marburg
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Abstract
Higher plant cells, which have been derived – as eukaryotic cells in general – from endosymbiotic events, are characterized by three genetic compartments: the nucleus/cytoplasm, mitochondria and plastids. The subgenomes, the nuclear genome, the chondriome and the plastome, respectively, are known to interact on various levels. Consequently a strict genetic coordination within the plant cell is indispensably required. Thus, the involved subgenomes are forming co-evolutionary units, which makes an interspecific exchange of organelles difficult and in some cases impossible. The combination of a nuclear genome from one species with a plastome of another species, for instance, quite frequently leads to deleterious phenotypes. Although this phenomenon, termed as nuclear-plastidial incompatibility, is widespread and has been known for more than 70 years, molecular mechanisms behind it have been elusive so far.
The cytoplasmic hybrid (cybrid) harboring the nuclear genome from Atropa belladonna [Ab] and the plastome from Nicotiana tabacum [(Nt)] shows an albino phenotype. Direct and reverse genetic approaches proved that the albino phenotype develops as a result of a defect in RNA editing of a N. tabacum specific editing site in the plastid ATPase alpha-subunit transcript, atpA. In N. tabacum the CCC proline codon at position 264 is changed to a CUC leucine codon by RNA editing on the mRNA, whereas at the homologous position within A. belladonna the leucine is already encoded on DNA as CTC. In the cybrid the CCC codon remains unaltered. Obviously a functional allele for the corresponding editing factor is missing within the A. belladonna nuclear genome.
In addition to further editing defects at N. tabacum specific editing sites within the [Ab(Nt)]-cybrid, editing was also found to be absent from the editing site ndhG-17 which was shown to be present and processed in both parental lines. Most probably, the recognition by the foreign site specific editing factor is impaired, because the predicted target sequence adjacent to the editing site is altered at one position two basepairs 5’ to the editing site in A. belladonna relative to N. tabacum. Although this editing defect is not expected to have a decisive impact on the albino phenotype of the [Ab(Nt)]-cybrid, this finding provides additional evidence for the strong co-evolution of editing factors and the corresponding editing sites.
A screen for editing sites in the plastid genome of Nicotiana glutinosa and the subsequent comparison to the plastid editing sites from N. tabacum revealed the presence of one species-specific editing site for each of the two species which is absent (T on DNA) from the plastome of the other species. This result confirms the fast evolution of editing sites leading to genetic differences even between closely related species. Thus, together with its functional importance plastid RNA editing fulfills all requirements for being a general factor for nuclear-plastidial incompatibility.
Contrasting these editing defects in interspecific combinations of cellular subgenomes, this work also uncovered surprising cases of heterologous editing. For example, the N. glutinosa specific editing site was surprisingly found to be processed in the nuclear background of N. tabacum, a phenomenon which is called “heterologous editing”. This finding emphasizes that heterologous editing can not longer be seen as an exception since it was found in four out of ten editing sites so far investigated. Obviously, functional alleles of editing factors are kept in some cases although the corresponding editing site they are serving is absent from the plastid genome (T on DNA).
The [Ab(Nt)]-cybrid exemplifies the crucial role for RNA editing in nuclear-plastidial incompatibility. However, the high frequency of heterologous RNA editing suggests that interspecific differences in plastid editing sites don’t necessarily have to trigger nuclear-plastidial incompatibility. Interspecific combinations of a nuclear genome with an alien plastome thus have to be tested in every single case for editing defects. If such defects are found, the impact on viability and development might be quite diverse depending in what gene the editing site resides and what codon is affected.
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Created: 2006Issued: 2006-12-21Updated: 2011-08-10
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Fachbereich Biologie
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Philipps-Universität Marburg
Language
ger
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DoctoralThesis
Keywords
EndosymbiosisRNA editingAtropaPlastidentransformationCybrideIncompatibilityPlastid transformationNicotianaChloroplast
DFG-subjects
ChloroplastRNS-EdierungInkompatibilitaetEndosymbiose
DDC-Numbers
570
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Poltnigg, Peter (132407124): RNA Edierung als molekulare Ursache für Kerngenom-Plastom-Inkompatibilität. : Philipps-Universität Marburg 2006-12-21. DOI: https://doi.org/10.17192/z2006.0912.
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This item has been published with the following license: In Copyright