Born with intronless ERF transcriptional factors: C4 photosynthesis inherits a legacy dating back 450 million years

The genus Flaveria , containing species at different evolutionary stages of the progression from C3 to C4 photosynthesis, is used as a model system to study the evolution of C4 photosynthesis. Here, we report chromosome-scale genome sequences for five Flaveria species, including C3, C4, and intermediate species. Our analyses revealed that both acquiring additional gene copies and recruiting ethylene responsive factor (ERF) cis -regulatory elements (CREs) contributed to the emergence of C4 photosynthesis. ERF transcriptional factors (TFs), especially intronless ERF TFs, were co-opted in dicotyledonous C4 species and monocotyledonous C4 species in parallel. These C4 species co-opted intronless ERF TFs originated from the Late Ordovician mass extinction that occurred ∼450 million years ago in coping with environmental stress. Therefore, this study demonstrated that intronless ERF TFs were acquired during the early evolution of plants and provided the molecular toolbox facilitating multiple subsequent independent evolutions of C4 photosynthesis. ### Competing Interest Statement The authors have declared no competing interest.