Catalyzes the transfer of a dimethylallyl group onto the adenine at position 37 in tRNAs that read codons beginning with uridine, leading to the formation of N6-(dimethylallyl)adenosine (i(6)A). Involved in the cis-type cytokinin biosynthesis. adenosine(37) in tRNA + dimethylallyl diphosphate = diphosphate + N(6)-dimethylallyladenosine(37) in tRNA Expressed ubiquitously, with highest expression in proliferating tissues. Not regulated by cytokinin, auxin or nitrate. No visible phenotype, due the redundancy with IPT2. Often chlorotic. Belongs to the IPP transferase family.