Exploring the possible role of hybridization in the evolution of photosynthetic pathways in Flaveria (Asteraceae), the prime model of C4 photosynthesis evolution

Flaveria (Asteraceae) is the prime model for the study of C 4 photosynthesis evolution and seems to support a stepwise acquisition of the pathway through C 3 -C 4 intermediate phenotypes, still existing in Flaveria today. Molecular phylogenies of Flaveria based on concatenated data matrices are currently used to reconstruct the complex sequence of trait shifts during C 4 evolution. To assess the possible role of hybridization in C 4 evolution in Flaveria , we re-analyzed transcriptome data of 17 Flaveria species to infer the extent of gene tree discordance and possible reticulation events. We found massive gene tree discordance as well as reticulation along the backbone and within clades containing C 3 -C 4 intermediate and C 4 -like species. An early hybridization event between two C 3 species might have triggered C 4 evolution in the genus. The clade containing all C 4 species plus the C 4 -like species F. vaginata and F. palmeri is robust but of hybrid origin involving F. angustifolia and F. sonorensis (both C 3 -C 4 intermediate) as parental lineages. Hybridization seems to be a driver of C 4 evolution in Flaveria and likely promoted the fast acquisition of C 4 traits. This new insight can be used in further exploring C 4 evolution and can inform C 4 bioengineering efforts.