Molecular cytogenetic analyses of haploid and allopolyploid Pellia species

The allopolyploid origin of several bryophyte species was reported approximately 20 years ago. Among them the best characterized is Pellia borealis, a hybrid of two cryptic sibling species: Pellia epiphylla-species N and P. epiphylla-species S. Genomes of the allopolyploid liverwort P. borealis and its progenitors were investigated using conventional as well as molecular cytogenetic techniques. The nuclear DNA content and cell cycle phase in the thallus nuclei was established using flow cytometry. Fluorescent differential staining, C-banding and fluorescent in situ hybridization (FISH) with 26S and 5S ribosomal DNA (rDNA) probes revealed new features of the chromosomes in the P. epiphylla-P. borealis complex. Some characteristics found in both the polyploid and haploid karyotypes support earlier suggestions about the allopolyploid origin of P. borealis. The banding pattern observed on P. borealis chromosomes suggests the occurrence of structural changes in the allopolyploid genome. The number and localization of rDNA sequences were established and simultaneous FISH with 26S and 5S rDNA probes showed colocalization of both types of ribosomal RNA (rRNA) genes in Pellia chromosomes. A nuclear DNA estimate showed that the P. borealis nuclear DNA content is about twice that of the largest known nuclear genome previously known in bryophytes.