Catalysis of the reaction: N(6)-dimethylallyladenine + S-adenosyl-L-methionine(1+) = S-methyl-5'-thioadenosine + discadenine + H+.
S-adenosyl-L-methionine:N6-(Delta2-isopentenyl)-adenine 3-(3-amino-3-carboxypropyl)-transferas