May catalyze both beta-1,3 and beta-1,4 glycosidic linkage on beta-D-glucan. Essential for (1,3;1,4)-beta-D-glucans synthesis in grasses and cereals (Poaceae). The mixed-linked glucans (which are not present in walls of dicotyledons or most other monocotyledonous plants) are particularly important constituents of the walls of the starchy endosperm and aleurone cells of cereal grains such as oats, wheat, rice and barley. They can account for up to 70% by weight of the wall (By similarity). Belongs to the glycosyltransferase 2 family. Plant cellulose synthase-like F subfamily.