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, especially in roots. [(1->4)-beta-D-glucosyl](n) + UDP-alpha-D-glucose = [(1->4)-beta-D-glucosyl](n+1) + H(+) + UDP Binds 2 Zn(2+) ions per subunit. Glycan metabolism; plant cellulose biosynthesis. Interacts with CESA1 and CESA6. Interacts with STL1 and STL2, but not with GOT1 (PubMed:27277162). Binds to CSI1 and CSI3 (PubMed:20616083, PubMed:24368796). Expressed in young plants, flowers and roots, and to a lower extent in leaves and stems. Localized in all cells except meristematic cells. Accumulates particularly in root caps, root hairs, epidermal layer, midveins of leaves and anthers. Not present in old tissues. Mostly expressed in cotyledons during all steps of embryogenesis, and decrease toward the bent-cotyledon stage. Mutants cev1 are dark green and contains more jasmonates and ethylene, that leads to shorter and thickened hypocotyls and roots, with prolific root hairs, and the accumulation of purple anthocyanins. They exhibit constitutive and high expression in leaves lamina of vegetative storage proteins (VSP1 and VSP2), basic chitinase CHI-B and plant defensin PDF1.2. In addition, this mutation confers resistance to powdery mildew pathogens such as E.cichoracearum, E.orontii and O.lycopersicum, to the bacterial pathogen P.syringae pv maculicola, and also to the green peach aphid M.persicae. Belongs to the glycosyltransferase 2 family. Plant cellulose synthase subfamily.