Drought stress is one of the most determinative factors of agriculture and plays a major role in limiting crop productivity. This limitation is going to rising through climate changes. However, plants have their own defense systems to moderate the adverse effects of climatic conditions. MicroRNA-mediated post-transcriptional gene regulation is one of these defense mechanisms. The root endophytic fungus Piriformospora indica enhances plant tolerance to environmental stress based on general and non-specific plant species mechanisms. In this work, we investigated the effects of drought and P. indica inoculation on the expression of two important miRNAs, miR159 and miR396, in rice plants. To this end, leaf samples were harvested at control (F.C.) and severe drought stress (25% F.C.) in P. indica-colonized and non-inoculated rice plants 4 weeks after fungal inoculation. We have observed contrary expression patterns of miR396 (down-regulated) and miR159 (up-regulated) under drought stress condition. However, both miRNAs showed up-regulation by P. indica inoculation. We have observed significant up-regulation of miR396 and miR159 by treatment of P. indica under drought stress condition. Regulation of growth, hyposensitivity response and bio-water saving pathways directly affected by MYB and GRF transcriptional factor. So, remarkable change of miR156 and miR396 could lead plant to be tolerable under drought stress by the fine regulation of MYB and GRF, respectively.
