An OsPRMT5‐OsAGO2/miR1875‐OsHXK1 module regulates rice immunity to blast disease

Rice ARGONAUTE2 (OsAGO2) is a core component of the rice RNA‐induced silencing complex (RISC), which is repressed by Magnaporthe oryzae (M. oryzae) infection. Whether and how OsAGO2‐mediated gene silencing plays a role in rice blast resistance and which sRNAs participate in this process are unknown. Our results indicate that OsAGO2 is a key immune player that manipulates rice defense responses against blast disease. OsAGO2 associates with the 24‐nt miR1875 and binds to the promoter region of HEXOKINASE1 (OsHXK1), which causes DNA methylation and leads to gene silencing. Our multiple genetic evidence showed that, without M. oryzae infection, OsAGO2/miR1875 RISC promoted OsHXK1 promoter DNA methylation and OsHXK1 silencing; after M. oryzae infection, the reduced OsAGO2/miR1875 led to a relatively activated OsHXK1 expression. OsHXK1 acts as a positive regulator of blast disease resistance that OsHXK1‐OE rice exhibited enhanced resistance, whereas Cas9‐Oshxk1 rice showed reduced resistance against M. oryzae infection. OsHXK1 may function through its sugar sensor activity as glucose induced defense‐related gene expression and reactive oxygen species (ROS) accumulation in Nipponbare and OsHXK1‐OE but not in Cas9‐Oshxk1 rice. OsAGO2 itself is delicately regulated by OsPRMT5, which senses M. oryzae infection and attenuates OsAGO2‐mediated gene silencing through OsAGO2 arginine methylation. Our study reveals an OsPRMT5‐OsAGO2/miR1875‐OsHXK1 regulatory module that fine tunes the rice defense response to blast disease. A rice defense module is initiated by sensing Magnaporthe oryzae infection via the protein arginine N‐methyltransferase OsPRMT5, activated by arginine methylation of OsARGONAUTE 2, amplified by OsHEXOKINASE 1 promoter DNA methylation via the microRNA miR1875, and implemented by activating multiple defense reposes.