Identification and characterization of an isopentenyltransferase (IPT) gene in soybean (Glycine max L.)

A putative isopentenyltransferase (IPT) encoding gene was identified from the soybean expressed sequence tag (EST) database, and the full-length gene was cloned with RACE. The gene was most similar to AtIPT5, an isopentenyltransferase gene in Arabidopsis, with respect to expression profile and sequence alignment. Southern hybridization showed that there were two copies (isoforms) of GmIPT in the soybean genome. Transgenic study with tobacco in the present study indicated that the protein encoded by the GmIPT1 gene could produce active cytokinins (CKs) in plants. RT-PCR revealed that the GmIPT1 gene may be expressed constitutively in several tissues. Promoter–GUS fusion revealed highly specific expression sites of GmIPT1 in roots, shoots and leaves, although these were not detected by Northern blot analysis, due to very low expression status. The isolated upstream regulatory sequence of GmIPT1 shared common transcription factor binding motifs with the corresponding regulatory regions of AtIPTs and OsIPTs. GmIPT1 expression was up-regulated by other phytohormones and chemicals, as indicated by the results of quantitative PCR and GUS activity examination in transgenic Arabidopsis. This is consistent with finding putative phytohormone and stress-responsive motifs in the promoter region. Involvement of putative signals and/or other factors in regulating GmIPT1 expression, and related control of CK production in higher plants are discussed.