Involved in the catabolism of syringate. Catalyzes the conversion of syringate to 3-O-methylgallate (3MGA) in the presence of tetrahydrofolate. Has weak activity with vanillate and 3-O-methylgallate. (6S)-5,6,7,8-tetrahydrofolate + syringate = (6S)-5-methyl-5,6,7,8-tetrahydrofolate + 3-O-methylgallate Optimum pH is 8.0 (in the presence of 1 mM tetrahydrofolate). Secondary metabolite metabolism; lignin degradation. Induced by growth on syringate. Mutant cannot grow on syringate, but grows on vanillate. Belongs to the GcvT family.