O-methyltransferase involved in the benzoxazinoid glucoside biosynthesis. Can use 2,4,7-trihydroxy-2H-1,4-benzoxazin-3(4H)-one 2-D-glucoside (TRIBOA-glucoside) as substrate, but not aglucone TRIBOA, caffeic acid, ferulic acid, apigenin or quercetin. S-adenosyl-L-methionine + TRIBOA beta-D-glucoside = DIMBOA beta-D-glucoside + H(+) + S-adenosyl-L-homocysteine kcat is 0.249 sec(-1) for TRIBOA-glucoside. Optimum pH is 7.0. Expressed in seedlings and newly formed crown roots. Highest expression in the scutellar node. Low to non detectable levels in cob, tassel and mature organs like husk or leaves. Peak of expression in 3- and 4-day-old seedlings. Belongs to the class I-like SAM-binding methyltransferase superfamily. Cation-independent O-methyltransferase family. COMT subfamily.