Phylogenetic relationships in the grass family (Poaceae) based on the nuclear single copy locus topoisomerase 6 compared with chloroplast DNA

Abstract

Phylogenetic relationships within the grass family were studied using a newly obtained locus of the nuclear single copy gene topoisomerase 6 (Topo6) spanning the four exons 8–11 and the chloroplast matK gene. Data were evaluated using maximum parsimony, maximum likelihood and Bayesian methods. All analyses showed genera Streptochaeta and Anomochloa as early diverging, followed by Pharus as sister to the rest of the Poaceae, and monophyly of the subfamily Anomochlooideae was supported by the nuclear dataset. The remaining grasses formed a strongly supported and monophyletic group, which split into the major clades BEP and PACMAD in the Topo6 analyses. Monophyly of the BEP clade was strongly supported by the Topo6 data. The results showed clearly incongruity between the two sets of data, such as the different subfamilial relationships of Bambusoideae, Ehrhartoideae and Pooideae. Most of the analysed species are representatives of subfamily Pooideae, which was analysed in more detail by PCR fragment length differences of another Topo6 region spanning the exons 17–19. Monophyly of Pooideae was strongly supported by the matK data, whereas the nuclear data placed Brachyelytrum outside of the remaining Pooideae. Relationships within the early evolutionary lineages remained largely unresolved in the phylogenetic trees, but the ‘core’ Pooideae (Aveneae/Poeae tribe complex and Hordeeae) were highly supported in all analyses. The differences in amplification lengths illustrate the tribe and subtribe classification of Pooideae. The comparatively conserved structure of the newly studied Topo6 region makes it a promising marker from the nuclear genome that could be successfully PCR-amplified to study higher-level phylogenetic relationships within grasses and perhaps between families within the order Poales.

Key words:

• BEP
• grasses
• matK
• phylogenetics
• Poaceae
• Pooideae
• Topo6
• topoisomerase

Acknowledgements

We would like to thank Barbara G. Briggs and Adam Marchant (The Royal Botanic Garden & the Domain, Sydney, Australia), Khidir W. Hilu (Virginia Polytechnic Institute, Blacksburg, USA), Natalia V. Tkach (Institute of Biology, Halle, Germany), Nikolai N. Tzvelev (Komarov Institute, St. Petersburg, Russia), and the herbaria listed in Table 1 for supplying plant material for our study. Further we are very grateful to Bärbel Hildebrandt for excellent technical support in our lab. A research grant of the German Research Foundation (DFG) is gratefully acknowledged.

Associate Editor: Nadia Bystriakova