Transfers dimethylallyl groups to AMP as part of the biosynthesis of cytokinin phytohormones like isopentenyl adenine or discadenine which controle spore formation and viability. AMP + dimethylallyl diphosphate = diphosphate + N(6)-(dimethylallyl)adenosine 5'-phosphate Belongs to the isopentenyl transferase family.