title: Evolution of genome size and chromosome number in the carnivorous plant genus Genlisea (Lentibulariaceae), with a new estimate of the minimum genome size in angiosperms.
abstract: OBJECTIVE
  Some species of Genlisea possess ultrasmall nuclear genomes, the smallest known among angiosperms, and some have been found to have chromosomes of diminutive size, which may explain why chromosome numbers and karyotypes are not known for the majority of species of the genus. However, other members of the genus do not possess ultrasmall genomes, nor do most taxa studied in related genera of the family or order. This study therefore examined the evolution of genome sizes and chromosome numbers in Genlisea in a phylogenetic context. The correlations of genome size with chromosome number and size, with the phylogeny of the group and with growth forms and habitats were also examined.
  
  
  METHODS
  Nuclear genome sizes were measured from cultivated plant material for a comprehensive sampling of taxa, including nearly half of all species of Genlisea and representing all major lineages. Flow cytometric measurements were conducted in parallel in two laboratories in order to compare the consistency of different methods and controls. Chromosome counts were performed for the majority of taxa, comparing different staining techniques for the ultrasmall chromosomes.
  
  
  RESULTS
  Genome sizes of 15 taxa of Genlisea are presented and interpreted in a phylogenetic context. A high degree of congruence was found between genome size distribution and the major phylogenetic lineages. Ultrasmall genomes with 1C values of <100 Mbp were almost exclusively found in a derived lineage of South American species. The ancestral haploid chromosome number was inferred to be n = 8. Chromosome numbers in Genlisea ranged from 2n = 2x = 16 to 2n = 4x = 32. Ascendant dysploid series (2n = 36, 38) are documented for three derived taxa. The different ploidy levels corresponded to the two subgenera, but were not directly correlated to differences in genome size; the three different karyotype ranges mirrored the different sections of the genus. The smallest known plant genomes were not found in G. margaretae, as previously reported, but in G. tuberosa (1C ≈ 61 Mbp) and some strains of G. aurea (1C ≈ 64 Mbp).
  
  
  CONCLUSIONS
  Genlisea is an ideal candidate model organism for the understanding of genome reduction as the genus includes species with both relatively large (∼1700 Mbp) and ultrasmall (∼61 Mbp) genomes. This comparative, phylogeny-based analysis of genome sizes and karyotypes in Genlisea provides essential data for selection of suitable species for comparative whole-genome analyses, as well as for further studies on both the molecular and cytogenetic basis of genome reduction in plants.
authors.affiliation: Department of Biology, Systematic Botany and Mycology and Geo-Bio Center LMU, Ludwig-Maximilians-Universität München, Menzinger Strasse 67, D 80638 Munich, Germany fleischmann@lrz.uni-muenchen.de.
authors.forename: Andreas
authors.initials: A
authors.lastname: Fleischmann
authors.affiliation: Waksman Institute of Microbiology, Rutgers University, 190 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Todd P
authors.initials: TP
authors.lastname: Michael
authors.affiliation: 1 Daniel Burnham Ct, San Francisco, CA 94109, USA.
authors.forename: Fernando
authors.initials: F
authors.lastname: Rivadavia
authors.affiliation: Department of Biology, Systematic Botany and Mycology and Geo-Bio Center LMU, Ludwig-Maximilians-Universität München, Menzinger Strasse 67, D 80638 Munich, Germany.
authors.forename: Aretuza
authors.initials: A
authors.lastname: Sousa
authors.affiliation: Waksman Institute of Microbiology, Rutgers University, 190 Frelinghuysen Road, Piscataway, NJ 08854, USA.
authors.forename: Wenqin
authors.initials: W
authors.lastname: Wang
authors.affiliation: Department of Botany and Biodiversity Research, Faculty of Life Sciences, University of Vienna, Rennweg 14, A 1030 Vienna, Austria.
authors.forename: Eva M
authors.initials: EM
authors.lastname: Temsch
authors.affiliation: Department of Botany and Biodiversity Research, Faculty of Life Sciences, University of Vienna, Rennweg 14, A 1030 Vienna, Austria.
authors.forename: Johann
authors.initials: J
authors.lastname: Greilhuber
authors.affiliation: Institute for Evolution and Biodiversity, University of Muenster, Hüfferstrasse 1, D 48149 Münster, Germany.
authors.forename: Kai F
authors.initials: KF
authors.lastname: Müller
authors.affiliation: Department of Biology, Systematic Botany and Mycology and Geo-Bio Center LMU, Ludwig-Maximilians-Universität München, Menzinger Strasse 67, D 80638 Munich, Germany.
authors.forename: Günther
authors.initials: G
authors.lastname: Heubl
mesh_terms: D032461:Chromosomes, Plant / Q000235:genetics*; D019143:Evolution, Molecular; D059646:Genome Size; D018745:Genome, Plant / Q000235:genetics*; D007621:Karyotyping; D019684:Magnoliopsida / Q000235:genetics* / Q000254:growth & development; D008677:Metaphase; D010788:Photosynthesis; D010802:Phylogeny; D011058:Pollen / Q000166:cytology; D013194:Staining and Labeling
keywords: Bladderwort; Genlisea; Lamiales; Lentibulariaceae; carnivorous plant; chromosome number; flow cytometry; genome miniaturization; genome size