title: Cytogenetic features of rRNA genes across land plants: analysis of the Plant rDNA database.
abstract: The online resource http://www.plantrdnadatabase.com/ stores information on the number, chromosomal locations and structure of the 5S and 18S-5.8S-26S (35S) ribosomal DNAs (rDNA) in plants. This resource was exploited to study relationships between rDNA locus number, distribution, the occurrence of linked (L-type) and separated (S-type) 5S and 35S rDNA units, chromosome number, genome size and ploidy level. The analyses presented summarise current knowledge on rDNA locus numbers and distribution in plants. We analysed 2949 karyotypes, from 1791 species and 86 plant families, and performed ancestral character state reconstructions. The ancestral karyotype (2n = 16) has two terminal 35S sites and two interstitial 5S sites, while the median (2n = 24) presents four terminal 35S sites and three interstitial 5S sites. Whilst 86.57% of karyotypes show S-type organisation (ancestral condition), the L-type arrangement has arisen independently several times during plant evolution. A non-terminal position of 35S rDNA was found in about 25% of single-locus karyotypes, suggesting that terminal locations are not essential for functionality and expression. Single-locus karyotypes are very common, even in polyploids. In this regard, polyploidy is followed by subsequent locus loss. This results in a decrease in locus number per monoploid genome, forming part of the diploidisation process returning polyploids to a diploid-like state over time.
authors.affiliation: Institut Botànic de Barcelona (IBB-CSIC-ICUB), Passeig del Migdia s/n, 08038, Barcelona, Catalonia, Spain.
authors.forename: Sònia
authors.initials: S
authors.lastname: Garcia
authors.affiliation: Institute of Biophysics, Academy of Sciences of the Czech Republic, Královopolská 135, Brno, 612 65, Czech Republic.
authors.forename: Ales
authors.initials: A
authors.lastname: Kovařík
authors.affiliation: School of Biological and Chemical Sciences, Queen Mary University of London, London E1 4NS, UK.
authors.forename: Andrew R
authors.initials: AR
authors.lastname: Leitch
authors.affiliation: Institut Botànic de Barcelona (IBB-CSIC-ICUB), Passeig del Migdia s/n, 08038, Barcelona, Catalonia, Spain.
authors.forename: Teresa
authors.initials: T
authors.lastname: Garnatje
mesh_terms: D032461:Chromosomes, Plant / Q000235:genetics; D018744:DNA, Plant / Q000235:genetics*; D004275:DNA, Ribosomal / Q000235:genetics*; D030541:Databases, Genetic; D019669:Embryophyta / Q000235:genetics*; D020459:Genes, rRNA / Q000235:genetics*; D059785:Karyotype; D010802:Phylogeny; D010944:Plants / Q000235:genetics*; D012337:RNA, Ribosomal, 18S / Q000235:genetics; D012341:RNA, Ribosomal, 5S / Q000235:genetics
chemical_list: D018744:DNA, Plant; D004275:DNA, Ribosomal; D012337:RNA, Ribosomal, 18S; D012341:RNA, Ribosomal, 5S
keywords: 18S-5.8S-26S; 5S; chromosome; genome evolution; rDNA loci; ribosomal DNA