In Plant Journal: new microRNA paper on THO2

THO2, core member of the THO/TREX complex, is required for micro RNA production in Arabidopsis

Francisco-Mangilet A.G., Karlsson P., Kim M.H., Eo H.J., Oh S.A., Kim J.H., Kulcheski F.R., Park S.K., Manavella P.A.

The THO/TREX complex mediates the transport of nascent mRNAs from the nucleus towards the cytoplasm in animals, and it has a role in small interfering RNA-dependent processes in plants. Here we describe five mutant alleles of Arabidopsis thaliana THO2, a core subunit of the plant THO/TREX complex. tho2 mutants present strong developmental defects resembling those in plants compromised in microRNA (miRNA) activity. In agreement, not only the levels of siRNAs, but also of mature miRNAs were reduced in tho2 mutants. As a consequence a feedback mechanism is triggered, increasing the amount of miRNA precursors, finally causing accumulation of miRNA-targeted mRNAs. Yeast two hybrid experiments and confocal microscopy showed that THO2 does not seem to interact with any of the known miRNA biogenesis components, but rather with the splicing machinery, implying an indirect role of THO2 in small RNA biogenesis. Using a RIP approach we found that THO2 is able to interact with miRNA precursors and that tho2 mutants fail to recruit such precursors into the miRNA-processing complex, explaining the reduction in the miRNA production in this mutant background. We also detected alterations in the splicing pattern of genes encoding Serine/Arginine-Rich (SR) proteins in tho2 mutants, supporting a previously unappreciated role of the THO/TREX complex in alternative splicing.