Involved in a key methylation step in both tocopherols (vitamin E) and plastoquinone synthesis. Catalyzes the conversion of 2-methyl-6-phytyl-1,4-hydroquinone (MPBQ) to 2,3-dimethyl-6-phytyl-1,4-hydroquinone (DMPQ, a substrate for tocopherol cyclase), and 2-methyl-6-solanyl-1,4-benzoquinone (MSBQ) to plastoquinone (By similarity). 2-methyl-6-phytyl-1,4-benzene-1,4-diol + S-adenosyl-L-methionine = 2,3-dimethyl-6-phytylbenzene-1,4-diol + H(+) + S-adenosyl-L-homocysteine 2-methyl-6-all-trans-nonaprenylbenzene-1,4-diol + S-adenosyl-L-methionine = H(+) + plastoquinol-9 + S-adenosyl-L-homocysteine 6-geranylgeranyl-2-methylbenzene-1,4-diol + S-adenosyl-L-methionine = 6-geranylgeranyl-2,3-dimethylbenzene-1,4-diol + H(+) + S-adenosyl-L-homocysteine Cofactor biosynthesis; tocopherol biosynthesis. Belongs to the class I-like SAM-binding methyltransferase superfamily. MPBQ/MBSQ MT family.