A canonical protein complex controls immune homeostasis and multipathogen resistance

Abstract

The calcium (Ca²⁺) sensor ROD1 (RESISTANCE OF RICE TO DISEASES1) is a master regulator of immunity in rice. By screening suppressors of <i>rod1</i> mutants, we show that ROD1 governs immune homeostasis by surveilling the activation of a canonical immune pathway. Mutations in <i>OsTIR</i> (<i>TIR-only protein</i>), <i>OsEDS1</i> (<i>enhanced disease susceptibility 1</i>), <i>OsPAD4</i> (<i>phytoalexin deficient 4</i>), and <i>OsADR1</i> (<i>activated disease resistance 1</i>) all abolish enhanced disease resistance of <i>rod1</i> plants. OsTIR catalyzes the production of second messengers 2'-(5″-phosphoribosyl)-5'-adenosine monophosphate (pRib-AMP) and diphosphate (pRib-ADP), which trigger formation of an OsEDS1-OsPAD4-OsADR1 (EPA) immune complex. ROD1 interacts with OsTIR and inhibits its enzymatic activity, whereas mutation of <i>ROD1</i> leads to constitutive activation of the EPA complex. Thus, we unveil an immune network that fine-tunes immune homeostasis and multipathogen resistance in rice.