miR398 regulation in rice of the responses to abiotic and biotic stresses depends on CSD1 and CSD2 expression.

MiR398 targets two Cu or Zn superoxide dismutases (CSD1 and CSD2) in Arabidopsis thaliana (L.) Heynh. Here we provide evidence that rice (Oryza sativa L.) miR398 mediates responses to abiotic and biotic stresses through regulating the expression of its target genes, Os-CSD1 and Os-CSD2. Rice plants were exposed to various stresses, including high Cu2+, high salinity, high light, methyl viologen, water stress, pathogens and ethylene, and the molecular response was investigated. Rice plants overexpressing Os-miR398 and the miR398-resistant form of Os-CSD2 were also exposed to these stresses. Both abiotic and biotic stresses significantly inhibited Os-miR398 expression and thus stimulated the expression of Os-CSD1 and Os-CSD2. The plant hormone ethylene produced an especially marked response. Transgenic rice lines that overexpressed Os-miR398 had a lower expression of CSD1 and -2 and were more sensitive to environmental stress. Conversely, transgenic rice lines which overexpressed the miR398-resistant form of Os-CSD2 showed more tolerance to high salinity and water stress than non-transgenic rice. We conclude that Os-miR398 regulates the responses of rice to a wide range of environmental stresses and to ethylene, and exerts its role through mediating CSDs expression and cellular ROS levels.