Hybridization and reticulation as driving forces in the evolution of grasses from temperate regions (grass subfamily Pooideae)?

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The grass subfamily Pooideae (~3300 species) is characteristic of the Earth´s temperate climate zones. This plant group is extremely meaningful for humans, because it has evolved major crop plants like wheat, barley, rye and oat. It is significant therefore (1) to identify the evolutionary lineages present within this subfamily, (2) to clarify their interrelations and (3) to determine the temporal sequence how they originated. In the preceding project phase we achieved a dense coverage of genera for DNA sequence data from the plastid and nuclear genome (matK-trnK region, repetitive nuclear ribosomal ITS). The data were analysed in conjunction with morphological, chromosomal and biogeographical research results. This led to several far-reaching taxonomic changes including the discovery of the new tribe Duthieeae among the early diverging lineages of Pooideae, to altered circumscriptions and re-arrangements of major evolutionary lineages (tribes, subtribes). On the whole, the molecular phylogenetic information for parts of the subfamily Pooideae and the placement of many genera in the trees seem to be at odds with classifications based on morphology. Frequent past hybridisation, partly even between genera from different tribes (intertribe hybridisation) therefore was discussed as a potential explanation of these inconsistencies. To obtain direct evidence on the role of past hybridisation and reticulate evolution, this project will focus on the biparentally inherited nuclear genome. Nuclear single copy genes (SCGs) have been increasingly used in recent years to analyse hybrid processes, introgression in homoploids, diploid-polyploid relationships, thus finally evolutionary reticulation. These non-repetitive markers preserve the evolutionary history frequently much better than the ribosomal arrays since they are less prone to gene conversion, a process, in which one parental copy is replaced by the other. Building on our preliminary work on topoisomerase 6 (Topo6) and acetyl-CoA carboxylase 1 (Acc1), we will sequence 5 exon/intron regions of these SCGs, which already have been successfully tested in our previous studies, and 4 from other SCGs. We will focus on the widely unresolved early diverging lineages of Pooideae (tribes Stipeae, Duthieeae, etc.) and the large Aveneae/Poeae tribe complex. For our study, 70 and 190 representative taxa have been selected from these groups. Conventional Sanger method and Next Generation Sequencing (NGS) will be used to gather DNA information. The data set of the SCGs will be compared with the plastid matK-trnK and nuclear ITS data, which have already been generated for the taxonomically completely overlapping sample of taxa. This analysis of differently inherited (uniparentally vs. biparentally) and differently evolving DNA regions is expected to give for the first time direct, DNA-based evidence of hybrid processes and has a high potential in their reconstruction.