Conservation and diversification of the molecular functions of YTHDF proteins

YTHDF proteins bind to N6 -methyladenosine (m6A) in eukaryotic mRNA to determine many cytoplasmatic properties of target transcripts. Vertebrates encode three YTHDF proteins whose possible functional specialization is debated. In land plants, the YTHDF clade has expanded from one member in basal lineages to eleven EVOLUTIONARILY CONSERVED C-TERMINAL REGION1-11 (ECT1-11) proteins in arabidopsis, named after the conserved YTH domain placed behind a divergent intrinsically disordered region. The origin and implications of YTHDF expansion in higher plants are unknown, as only three of these eleven m6A readers have been studied. Here, we show that stimulation of primordial cell division relies on an ancestral molecular function of the m6A-YTHDF axis that was present in the first land plants and remained conserved over YTHDF diversification, as it appears in all major clades of YTHDF proteins in flowering plants. Nevertheless, lineage-specific neo-functionalization of ECT1, ECT9 and ECT11 happened after late duplication events, and involves altered properties mainly of the IDRs. Metazoan YTHDFs cannot provide stimulation of stem cell division in arabidopsis, suggesting different molecular activities of YTHDF proteins across kingdoms. ### Competing Interest Statement The authors have declared no competing interest.