OsAGO2 controls ROS production and the initiation of tapetal PCD by epigenetically regulating OsHXK1 expression in rice anthers

Proteins of the ARGONAUTE (AGO) family function in the epigenetic regulation of gene expression. Although the rice (Oryza sativa) genome encodes 19 predicted AGO proteins, few of their functions have thus far been characterized. Here, we show that the AGO protein OsAGO2 regulates anther development in rice. OsAGO2 was highly expressed in anthers. Knockdown of OsAGO2 led to the overaccumulation of reactive oxygen species (ROS) and abnormal anther development, causing premature initiation of tapetal programmed cell death (PCD) and pollen abortion. The expression level of Hexokinase 1 (OsHXK1) increased significantly, and the methylation levels of its promoter decreased, in plants with knocked-down OsAGO2 expression. Overexpression of OsHXK1 also resulted in the overaccumulation of ROS, premature initiation of PCD, and pollen abortion. Moreover, knockdown of OsHXK1 restored pollen fertility in OsAGO2 knockdown plants. Chromatin im-munoprecipitation assays demonstrated that OsAGO2 binds directly to the OsHXK1 promoter region, suggesting that OsHXK1 is a target gene of OsAGO2. These results indicate that OsHXK1 controls the appropriate production of ROS and the proper timing of tapetal PCD and is directly regulated by OsAGO2 through epigenetic regulation.