Expression and characterization of rice putative PAUSED gene.

In Arabidopsis, PAUSED (PSD) encodes the ortholog of los1p/exportin-t, which mediates the nuclear export of transfer RNA (tRNA) in yeast and mammals. However, in monocot plants such as rice, knowledge of the corresponding ortholog is limited, and its effects on growth development and productivity remain unknown. In this study, we verified a rice transfer-DNA insertional mutant psd line and analyzed its phenotypes; the mutant displayed severe morphological defects including retarded development and low fertility compared with wild-type rice. Examining intronless tRNA-Tyr and intron-containing pre-tRNA-Ala expression levels in cytoplasmic and nuclear fraction with Northern blot analysis between wild-type and mutant leaf tissue suggested that rice PSD might be involved in tRNA export from the nucleus to the cytoplasm. Additionally, reverse transcription-polymerase chain reaction analysis revealed that PSD transcript was expressed throughout normal rice plant development, and subcellular localization assays showed that rice PSD protein was present in both the nucleus and cytoplasm. In summary, our data implied that the putative PSD gene might be indispensable for normal rice development and its function might be the same as that of Arabidopsis PSD.