title: A bicontinental origin of polyploid Australian/New Zealand Lepidium species (Brassicaceae)? Evidence from genomic in situ hybridization.
abstract: OBJECTIVE
  Incongruence between chloroplast and nuclear DNA phylogenies, and single additive nucleotide positions in internal transcribed spacer (ITS) sequences of polyploid Australian/New Zealand (NZ) Lepidium species have been used to suggest a bicontinental hybrid origin. This pattern was explained by two trans-oceanic dispersals of Lepidium species from California and Africa and subsequent hybridization followed by homogenization of the ribosomal DNA sequence either to the Californian (C-clade) or to the African ITS-type (A-clade) in two different ITS-lineages of Australian/NZ Lepidium polyploids.
  
  
  METHODS
  Genomic in situ hybridization (GISH) was used to unravel the genomic origin of polyploid Australian/NZ Lepidium species. Fluorescence in situ hybridization (FISH) with ribosomal DNA (rDNA) probes was applied to test the purported ITS evolution, and to facilitate chromosome counting in high-numbered polyploids.
  
  
  RESULTS
  In Australian/NZ A-clade Lepidium polyploids, GISH identified African and Australian/NZ C-clade species as putative ancestral genomes. Neither the African nor the Californian genome were detected in Australian/NZ C-clade species and the Californian genome was not detected in Australian/NZ A-clade species. Five of the eight polyploid species (from 7x to 11x) displayed a diploid-like set of rDNA loci. Even the undecaploid species Lepidium muelleriferdinandi (2n = 11x = 88) showed only one pair of each rDNA repeat. In A-clade allopolyploids, in situ rDNA localization combined with GISH corroborated the presence of the African ITS-type.
  
  
  CONCLUSIONS
  The nuclear genomes of African and Australian/NZ C-clade species were detected by GISH in allopolyploid Australian/NZ Lepidium species of the A-clade, supporting their hybrid origin. The presumed hybrid origin of Australian/NZ C-clade taxa could not be confirmed. Hence, it is assumed that Californian ancestral taxa experienced rapid radiation in Australia/NZ into extant C-clade polyploid taxa followed by hybridization with African species. As a result, A-clade allopolyploid Lepidium species share the Californian chloroplast type and the African ITS-type with the C-clade Australian/NZ polyploid and African diploid species, respectively.
authors: Universität Osnabrück, Abteilung Botanik, Barbarastrasse 11, 49076 Osnabrück, Germany. Tomiworld@gmx.de
authors: Tom
authors: T
authors: Dierschke
authors: Terezie
authors: T
authors: Mandáková
authors: Martin A
authors: MA
authors: Lysak
authors: Klaus
authors: K
authors: Mummenhoff
mesh_terms: D001315:Australia; D005075:Biological Evolution; D032461:Chromosomes, Plant / Q000235:genetics; D021903:DNA, Ribosomal Spacer / Q000235:genetics; D035264:Flowers / Q000166:cytology / Q000235:genetics; D018745:Genome, Plant / Q000235:genetics*; D005843:Geography; D017403:In Situ Hybridization; D007211:Indoles; D029686:Lepidium / Q000235:genetics*; D008938:Mitosis; D009520:New Zealand; D011123:Polyploidy
chemical_list: D021903:DNA, Ribosomal Spacer; D007211:Indoles; C007293:DAPI