, a Plant-specific Casein Kinase 1, Negatively Regulates Flowering and Phosphorylates Histone H3 in Vitro.

thaliana (), a family of the plant-specific casein kinase 1 (CK1), have been implicated collectively in multiple biological processes including flowering. Three of the four () have been characterized, however, little is known about , the most divergent member of Here, we demonstrated that disruption of transcript in caused early flowering with retarded leaf growth under long-day conditions. In vitro kinase assay showed the nuclear protein MLK3 phosphorylated histone 3 at threonine 3 (H3T3) and mutation of a conserved residue (K146R) abolished the catalytic activity. Ectopic expression of but not () rescued the morphological defects of , indicating that an intact MLK3 is critical for maintaining proper flowering time. Transcriptomic analysis revealed that the floral repressor C () was down-regulated significantly in , suggesting that negatively regulates flowering. Hence, plays a role in repressing the transition from vegetative to reproductive phase in . thaliana. This study sheds light on the delicate control of flowering time by . thaliana specific to the plant kingdom.