Gene expression in the 7-day-old cotyledons of Col-0 and ckg

Cytokinin (CK) has been known as a cell proliferation activator for a long time in plants; however, its regulatory mechanism in cell division and expansion still remains unclear. Here we revealed that a bHLH transcription factor, CKG (CYTOKININ-RESPONSIVE GROWTH REGULATOR) mediates CK-dependent regulation of cell expansion and cell cycle. Overexpression of CKG increased cell size in a ploidy-independent manner and promoted S-phase entry of cell-cycle especially at early developmental stage, and pleiotropically enhanced organ growth from embryogenesis to reproductive stage, particularly cotyledons. In contrast, ckg loss-of-function mutant exhibited smaller cotyledons. CKG regulates the expression of genes mainly involved in regulation of cell cycle and macromolecule synthesis. We propose that CKG provides a regulatory module of cell cycle and organ growth in CK response. Gene expression in the 7-day-old cotyledons of Col-0 and ckg mutant was measured. Two biological replicates of Col-0 and three biological replicates of ckg line were used.