Abstact

The calcium (Ca2+) sensor ROD1 (RESISTANCE OF RICE TO DISEASES1) is a master regulator of immunity in rice. By screening suppressors of rod1 mutants, we show that ROD1 governs immune homeostasis by surveilling the activation of a canonical immune pathway. Mutations in OsTIR (TIR-only protein), OsEDS1 (enhanced disease susceptibility 1), OsPAD4 (phytoalexin deficient 4), and OsADR1 (activated disease resistance 1) all abolish enhanced disease resistance of rod1 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 ROD1 leads to constitutive activation of the EPA complex. Thus, we unveil an immune network that fine-tunes immune homeostasis and multipathogen resistance in rice.