Characterization of KS activity for ZmTPS1, ZmKSL3, and ZmKSL5. A, GC-MS analysis (272 m/z extracted ion chromatographs) of the enzymatic products of ZmTPS1, ZmKSL5, and ZmKSL3. B, Production of ent-kaurene by ZmTPS1, ZmKSL5, and ZmKSL3 transiently expressed in N. benthamiana with An2 (ZmCPS2). GC-MS analysis (272 m/z extracted ion chromatographs) was carried out using leaf extract after infiltration for 5 d. Agrobacterium GV3101 harboring P19 was coinfiltrated in all treatment. Authentic ent-kaurene (retention time, 17.80 min.) made by OsKS was used for retention time and mass spectra comparison. EV, Empty vector control.