Abstract: In order to reveal the physiological functions of the small subunit of geranylgeranyl pyrophosphate synthase(GGPPS),a cDNA sequence encoding the small subunit of GGPPS was isolated from tobacco(Nicotiana tabacum) by in silico cloning combined with RT-PCR and SMART RACE technology,and designated as NtGGPPS5(GenBank Number KF316932),the gene was 1320 bp in length and encoded a putative protein of 332 amino acids.This deduced amino acid sequence shared 92% identity with Solanum lycopersicum(XP_004246572) and Solanum pennellii(ADZ24721),and possessed a characterized Asp-rich motif of isoprenyl synthase family.Phylogenetic analysis revealed that the plant GGPPSs had two branches:large subunit and small subunit,NtGGPPS5 belonged in the latter.Meanwhile,the results of real-time quantitative PCR analysis indicated that NtGGPPS5 was transcribed in root,stalk,leaf and bud,the order of NtGGPPS5 expression level was bud>leave>stalk>root.