Catalyzes the formation of N(7)-methylguanine at position 46 (m7G46) in tRNA. guanosine(46) in tRNA + S-adenosyl-L-methionine = N(7)-methylguanosine(46) in tRNA + S-adenosyl-L-homocysteine tRNA modification; N(7)-methylguanine-tRNA biosynthesis. Forms a complex with TRM82. Significant reduction in pathogenicity on the host plants. Mutants develop penetration hyphae into cellophane, suggesting that appressoria of the mutants retain basic function for penetration. However, they fail to develop intracellular penetration hyphae into epidermis of the host plants. Belongs to the class I-like SAM-binding methyltransferase superfamily. TrmB family.