title: Organization, differential expression and methylation of rDNA in artificial Solanum allopolyploids.
abstract: Uniparental activity of ribosomal RNA genes (rDNA) in interspecific hybrids is known as nucleolar dominance (ND). To see if difference in rDNA intergenic spacers (IGS) might be correlated with ND, we have used artificial Solanum allopolyploids and back-crossed lines. Combining fluorescence in situ hybridization and quantification of the level of the rRNA precursor by real-time PCR, we demonstrated that an expression hierarchy exists: In leaves, roots, and petals of the respective allopolyploids, rDNA of S lycopersicum (tomato) dominates over rDNA of S. tuberosum (potato), whereas rDNA of S. tuberosum dominates over that of the wild species S. bulbocastanum . Also in a monosomic addition line carrying only one NOR-bearing chromosome of tomato in a potato background the dominance effect was maintained. These results demonstrate that there is possible correlation between transcriptional dominance and number of conservative elements downstream of the transcription start in the Solanum rDNA. In anthers and callus tissues under-dominant rDNA was slightly (S. lycopersicum/S. tuberosum) or strongly (S. tuberosum/S. bulbocastanum) expressed indicating developmental modulation of ND. In leaves and petals, repression of the respective parental rDNA correlated with cytosine methylation at certain sites conserved in the IGS, whereas activation of under-dominant rDNA in anthers and callus tissues was not accompanied by considerable changes of the methylation pattern.
authors.affiliation: Department of General Genetics, Center of Plant Molecular Biology (ZMBP), University of Tübingen, Auf der Morgenstelle 28, Tübingen, 72076, Germany.
authors.forename: Nataliya Y
authors.initials: NY
authors.lastname: Komarova
authors.forename: Thomas
authors.initials: T
authors.lastname: Grabe
authors.forename: Dirk J
authors.initials: DJ
authors.lastname: Huigen
authors.forename: Vera
authors.initials: V
authors.lastname: Hemleben
authors.forename: Roman A
authors.initials: RA
authors.lastname: Volkov
mesh_terms: D001483:Base Sequence; D003433:Crosses, Genetic; D019175:DNA Methylation; D018744:DNA, Plant / Q000737:chemistry / Q000235:genetics / Q000302:isolation & purification; D004275:DNA, Ribosomal / Q000235:genetics* / Q000378:metabolism; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D020869:Gene Expression Profiling; D018506:Gene Expression Regulation, Plant; D017404:In Situ Hybridization, Fluorescence; D008969:Molecular Sequence Data; D011123:Polyploidy; D012335:RNA, Ribosomal / Q000235:genetics / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017422:Sequence Analysis, DNA; D012689:Sequence Homology, Nucleic Acid; D032322:Solanum / Q000235:genetics*
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal; D021903:DNA, Ribosomal Spacer; D012335:RNA, Ribosomal; C065039:RNA, ribosomal, 25S