Linking key steps of microRNA biogenesis by TREX-2 and the nuclear pore complex in Arabidopsis.

Unlike in metazoans, the stepwise biogenesis of microRNAs (miRNAs) in plants occurs within the nucleus. Whether or how the major steps in miRNA biogenesis are coordinated is largely unknown. Here we show that the plant TREX-2 complex promotes multiple steps in miRNA biogenesis, including transcription, processing and nuclear export. THP1 and SAC3A-the core subunits of TREX-2-interact and colocalize with RNA polymerase II to promote the transcription of MIR genes in the nucleoplasm. TREX-2 interacts with the microprocessor component SERRATE and promotes the formation of dicing bodies in the nucleoplasm. THP1 also interacts and colocalizes with the nucleoporin protein NUP1 at the nuclear envelope. NUP1 and THP1 promote the nuclear export of miRNAs and ARGONAUTE1. These results suggest that TREX-2 coordinates the transcription, processing and export steps in miRNA biogenesis to ensure efficient miRNA production.