Required for correct initiation of floral organ primordia and for proper development of organ primordia. Phosphorylates in vitro ASF1B/SGA1, the C-terminal part of TKI1 and histone H3. ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Oligomerization is required for activity. May be activated by trans-autophosphorylation. Higher activity during G2/M phase and G1 phase compared to S phase. Homooligomer. Interacts with TKI1 and ASF1B/SGA1. Most abundant in developing floral meristem. Also expressed in maturing flowers, developing seeds, mature leaves and roots. Barely detected in stems. Expressed at constant level during the cell cycle. The first coiled coil domain is essential for oligomerization. Autophosphorylation on both phosphoserine and phosphothreonine. Belongs to the protein kinase superfamily. Ser/Thr protein kinase family.