Born with intronless ERF transcriptional factors: C₄photosynthesis inherits a legacy dating back 450 million years

SummaryThe genusFlaveria, containing species at different evolutionary stages of the progression from C3to C4photosynthesis, is used as a model system to study the evolution of C4photosynthesis. Here, we report chromosome-scale genome sequences for fiveFlaveriaspecies, 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 C4photosynthesis. ERF transcriptional factors (TFs), especially intronless ERF TFs, were co-opted in dicotyledonous C4species and monocotyledonous C4species in parallel. These C4species 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 C4photosynthesis.