RiceOsPAD4functions differently fromArabidopsisAtPAD4in host‐pathogen interactions

Summary The extensively studied A rabidopsis phytoalexin deficient 4 ( A t PAD 4 ) gene plays an important role in A rabidopsis disease resistance; however, the function of its sequence ortholog in rice is unknown. Here, we show that rice O s PAD 4 appears not to be the functional ortholog of A t PAD 4 in host‐pathogen interactions, and that the Os PAD 4 encodes a plasma membrane protein but that A t PAD 4 encodes a cytoplasmic and nuclear protein. Suppression of Os PAD 4 by RNA interference ( RNA i) increased rice susceptibility to the biotrophic pathogen X anthomonas oryzae pv. oryzae ( X oo ), which causes bacteria blight disease in local tissue. O s PAD 4 ‐ RNA i plants also show compromised wound‐induced systemic resistance to X oo . The increased susceptibility to X oo was associated with reduced accumulation of jasmonic acid ( JA ) and phytoalexin momilactone A ( MOA ). Exogenous application of JA complemented the phenotype of O s PAD 4 ‐ RNA i plants in response to X oo . The following results suggest that O s PAD 4 functions differently than A t PAD 4 in response to pathogen infection. First, O s PAD 4 plays an important role in wound‐induced systemic resistance, whereas A t PAD 4 mediates systemic acquired resistance. Second, O s PAD 4 ‐involved defense signaling against X oo is JA ‐dependent, but A t PAD 4 ‐involved defense signaling against biotrophic pathogens is salicylic acid‐dependent. Finally, O s PAD 4 is required for the accumulation of terpenoid‐type phytoalexin MOA in rice‐bacterium interactions, but A t PAD 4 ‐mediated resistance is associated with the accumulation of indole‐type phytoalexin camalexin.