Objectives We analyzed the spatiotemporal expression of rice oligopeptide transport genes in different organs of rice, in order to understand the mechanism of the absorption, transport and distribution of oligopeptides and other nutrients in rice.

Methods Employing the genome of japonica rice variety Nipponbare as the template, the promoter sequences of the nine genes belonging to the PT subfamily of the rice oligopeptide transport gene family were separately cloned and inserted in front of the glucuronidase (GUS) protein coding region in the pCAMBIA1301 vector, thereby forming the promoter-induced GUS protein expression vectors. Through Agrobacterium, transgenic rice plants with GUS protein expression respectively induced by the nine rice oligopeptide transport gene promoters were prepared. Field experiment was carried out during the natural growing season. At the heading and flowering stage, organ samples such as roots, stems, leaves, and spikelets of rice were cut and immersed in GUS staining solution for histochemical staining. Stereomicroscopic observation and photography were conducted. The expression profiles of the nine rice oligopeptide transport genes in different organs in the rice gene expression database RiceXPro were analyzed, and the cis-acting elements of the promoter sequences of the nine rice oligopeptide transport genes were analyzed using the PlantCare database.

Results The nine promoters of rice oligopeptide transport gene family could induce GUS protein to express strongly in rice nodules, and seven of them could induce GUS protein to express strongly in rice inner and outer husks, which were OsOPT1, OsOPT2, OsOPT4, OsOPT5, OsOPT7, OsOPT8 and OsOPT9. The expression profile of RiceXPro rice gene expression database showed that the expression of OsOPT5 and OsOPT6 had strong specificity, which were strongly expressed only in the late stage of anther development and were not detected in other organs. In addition, multiple GA and abscisic acid response elements were found in the promoters of rice oligopeptide transport gene family.

Conclusions The promoter activity of the rice oligopeptide transporter gene family has strong organ-specificity. The expression of GUS protein is strongly induced in the node region of rice, where 9 rice oligopeptide transporter gene promoters are located, indicating that these genes participate in the exchange and allocation of nutrients among different organs of rice and play a role in the response to auxin and abscisic acid signals.