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Cellulose is the most abundant biopolymer on Earth. Three cellulose synthases (CESA4, CESA7 and CESA8) are necessary for cellulose production in the secondary cell walls of Arabidopsis. Little is known about how expression of these CESA genes is regulated. We recently identified a cis‐regulatory element (M46RE) that is recognized by MYB46, which is a master switch for secondary wall formation in Arabidopsis. A genome‐wide survey of promoter sequences for the presence of M46REs led to the hypothesis that MYB46 may function as a direct regulator of all three secondary wall‐associated cellulose synthase genes: CESA4, CESA7 and CESA8. We tested this hypothesis using several lines of experimental evidence. All three CESA genes are highly up‐regulated by both constitutive and inducible over‐expression of MYB46 in planta. Using a steroid receptor‐based inducible activation system, we show …