Catalytic subunit of cellulose synthase terminal complexes ('rosettes'), required for beta-1,4-glucan microfibril crystallization, a major mechanism of the cell wall formation. Involved in the primary cell wall formation. Required during embryogenesis for cell elongation, orientation of cell expansion and complex cell wall formations, such as interdigitated pattern of epidermal pavement cells, stomatal guard cells and trichomes. Plays a role in lateral roots formation, but seems not necessary for the development of tip-growing cells such as root hairs. The presence of each protein CESA1 and CESA6 is critical for cell expansion after germination