Focal Accumulation of ROS Can BlockPyricularia oryzaeEffector BAS4-Expression and Prevent Infection in Rice

The reactive oxygen species (ROS) burst is the most common plant immunity mechanism to prevent pathogen infection, although the exact role of ROS in plant immunity has not been fully elucidated. We investigated the expression and translocation ofOryza sativarespiratory burst oxidase homologue B (OsRBOHB) during compatible and incompatible interactions between rice epidermal cells and the pathogenic fungusPyricularia oryzae(syn.Magnaporthe oryzae). We characterized the functional role of ROS focal accumulation around invading hyphae duringP. oryzaeinfection process using the OsRBOHB inhibitor diphenyleneiodonium (DPI) and the actin filament polymerization inhibitor cytochalasin (Cyt) A. OsRBOHB was strongly induced during incompatible rice-P. oryzaeinteractions, and newly synthesized OsRBOHB was focally distributed at infection sites. High concentrations of ROS focally accumulated at the infection sites and suppressed effector biotrophy-associated secreted (BAS) proteins BAS4 expression and invasive hyphal growth. DPI and Cyt A abolished ROS focal accumulation and restoredP. oryzaeeffector BAS4 expression. These results suggest that ROS focal accumulation is able to function as an effective immune mechanism that blocks some effectors including BAS4-expression duringP. oryzaeinfection. Disruption of ROS focal accumulation around invading hyphae enables successfulP. oryzaecolonization of rice cells and disease development.