A MACPF Protein OsCAD1 Balances Plant Growth and Immunity Through Regulating Salicylic Acid Homeostasis in Rice

Unraveling the mechanisms behind plant growth and immunity contributes to effective crop improvement. Membrane attack complex/perforin (MACPF) domain proteins play vital roles in innate and adaptive immunity in vertebrates; however, their molecular functions in plants remain largely unexplored. Here, we isolated and characterized a rice mutant, Oryza sativa constitutively activated cell death 1 (oscad1), which exhibited a lesion mimic phenotype and growth inhibition with increased cell death, elevated ROS accumulation, and enhanced resistance to bacterial blight Xanthomonas oryzae pv. Oryzae (Xoo) and Magnaporthe oryzae. OsCAD1 encodes an MACPF protein, OsCAD1/OsMACPF1, localized in the plasma membrane, cytosol, and nucleus, with a broad expression pattern in tissues. An F416L substitution in OsCAD1 affects its stability and abundance. OsCAD1 knockout lines displayed severe lesion mimic leaves, growth retardation, and eventual death. Both oscad1 and OsCAD1 knockout lines showed increased salicylic acid (SA) levels with the latter showing even higher levels, while OsCAD1-overexpressing lines maintained uninduced SA levels during Xoo infection, resulting in decreased resistance. Knockout of the SA biosynthetic enzyme OsPAL4 in the oscad1 mutant partially alleviated the lesion mimic phenotype and growth inhibition without impacting Xoo resistance. Our findings indicate that OsCAD1 negatively regulates SA levels to modulate plant growth and immunity.