S-adenosyl-L-methionine-dependent N-methyltransferase that catalyzes a nitrogen methylation involved in vindoline biosynthesis (PubMed:20956330, PubMed:21802100). Displays a strict requirement for a 2,3-dihydro bond in the aspidosperma skeleton (PubMed:20956330). Can use 2,3-dihydrotabersonine, 2,3-dihydro-3-hydroxytabersonine and 2,3,6,7-tetraydro-3-hydroxytabersonine as substrates, but not tabersonine, vincadifformine, picrinine, 21-hydroxycyclolochnericine, tryptamine, norharmane, harmaline, catharanthine, norajmaline, ajmaline, serpentine, ajmalicine, yohimbine or gamma-tocopherol (PubMed:20956330, PubMed:26848097). (3R)-3-hydroxy-16-methoxy-2,3-dihydrotabersonine + S-adenosyl-L-methionine = deacetoxyvindoline + H(+) + S-adenosyl-L-homocysteine Inhibited by gamma-tocopherol. kcat is 2.47 sec(-1) for 2,3-dihydrotabersonine. kcat is 5.4 sec(-1) for S-adenosyl-L-methionine. Alkaloid biosynthesis; vindoline biosynthesis. Homodimer. Up-regulated upon methyl jasmonate treatment. Belongs to the class I-like SAM-binding methyltransferase superfamily. gTMT family. Extended N-terminus.