S-adenosyl-L-methionine-dependent methyltransferase responsible for the addition of the methyl group in the formation of N6-methyl-N6-threonylcarbamoyladenosine at position 37 (m(6)t(6)A37) of the tRNA anticodon loop of tRNA(Ser)(GCU) (PubMed:25063302). The methyl group of m(6)t(6)A37 may improve the efficiency of the tRNA decoding ability (By similarity).