A SiPf40 gene was identified from an immature seed cDNA library of foxtail millet (Setaria italica). This gene encodes for a 29.4 KDa protein containing eight potential transmembrane domains and a highly conserved ZIP signature motif typical of ZIPs (zinc or iron transporter proteins) family. Other SiPf40 potential homologous genes have also been identified in rice, maize, wheat and Arabidopsis by Southern analysis. Expression data showed that this gene is preferentially expressed in millet hypocotyl and bud; however, a minimal level of constitutive expression could be detected in other foxtail millet tissues. Overexpression of SiPf40 gene causes extra branches in tobacco and extra tillering in millet associated with vessel enlarging and xylary fibers increasing, whereas the tiller number decreases in SiPf40 gene silenced plants. Moreover, IAA content decreased significantly in shoot apex of the transgenic tobacco overexpressing SiPf40 gene. All together, these morphological alterations indicate that SiPf40 gene is essential for lateral shoots growth.