Chromosome evolution in wild oat grasses (Aveneae) revealed by molecular phylogeny.

Karyotype structures revealed by in situ hybridization with ribosomal and satellite DNAs and fluorochrome staining of AT- or GC-rich regions are reported for 23 diploid to tetraploid taxa of Aveneae genera Arrhenatherum, Avena, Helictotrichon, and Pseudarrhenatherum. Chromosomal features are compared with a molecular phylogeny generated on nuclear ribosomal (ITS, 5S) and chloroplast (matK) DNA sequences. Ancestral chromosomal character states are (1) two satellite chromosomes per set of x = 7, (2) 5S rDNA localized in nonsatellite chromosomes, (3) large chromosomes with (4) rather equal lengths of their respective chromosome arms, (5) sets with strong variance of chromosome lengths, (6) absence or small amounts of heterochromatin, and (7) absence or no detectable amplification of the satellite DNAs tested. Overall, most karyotype characteristics are species specific, but common patterns were found for the species of two large subgenera of Helictotrichon. Pseudarrhenatherum, although nested in the molecular phylogeny within Helictotrichon subgenus Helictotrichon, deviates strongly in karyotype characters such as Arrhenatherum as sister of Avena. The karyotype of Helictotrichon jahandiezii, sister to the clade of Helictotrichon subgenera Helictotrichon, Avena, and Arrhenatherum, strongly resembles that of Avena macrostachya. Karyotype features suggest that perennial A. macrostachya and H. jahandiezii are close to the C-genome species of annual Avena, whereas the Avena A genome resembles that of Arrhenatherum.