Abstract

Because of tremendous variation in anatomy, floral morphology, and breeding systems as well as its worldwide distribution covering very different environments, the Oleeae tribe (Oleaceae) presents a very interesting biological model to study plant diversification and molecular evolution patterns. However, without a robust phylogenetic framework, our understanding of the mechanisms, which led to this diversification, is still too limited to accurately describe the evolutionary and biogeographic history of this tribe. Reconstruction of the evolutionary history of the Oleeae tribe and the phylogenetic relationships between its species were thus at the core of this work. This was notably addressed by applying a genome skimming strategy in order to assembly complete plastid genomes (mean size _{155’000 bp) and nearly complete nuclear ribosomal DNA (ETS, 18S, ITS1 , 5.8S, ITS2 , and 26S) (mean size} 7’000 bp) of 74 taxa encompassing all 18 recognized genera of Oleeae. This work has led to significant progress in resolving the phylogenetic relationships within the tribe at different taxonomic levels. We demonstrated that the use of a shotgun approach is a highly suitable method to generate complete plastomes (ptDNA) and nuclear ribosomal DNA (nrDNA), even on herbarium sample. We showed the high suitability of the complete plastid genome for constructing a robust and high-resolution phylogeny of the Oleeae tribe and provided new insights into the biogeographic history and the evolution of it breeding system. We also demonstrated that nuclear ribosomal DNA structure appears to be influenced by climatic factors. This latter lie in line with the predictions of the thermostability hypothesis and suggest that this topic needs to be looked into more in detail for better mechanistic understanding of genome evolution.