Catalytic subunit of cellulose synthase terminal complexes ('rosettes'), required for beta-1,4-glucan microfibril crystallization, a major mechanism of the cell wall formation. [(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. Belongs to the glycosyltransferase 2 family. Plant cellulose synthase subfamily. Lacks the conserved zinc finger domain, which is one of the features of the CESA family. Could be the product of a pseudogene.