%D 2008 %0 MEDLINE %T Rice XB15 , a protein phosphatase 2C , negatively regulates cell death and XA21-mediated innate immunity . %J PLoS Biol %V 6 %P e231 %A Park CJ %A Peng Y %A Chen X %A Dardick C %A Ruan D %A Bart R %A Canlas PE %A Ronald PC %M pub18817453 %X Perception of extracellular signals by cell surface receptors is of central importance to eukaryotic development and immunity . Kinases that are associated with the receptors or are part of the receptors themselves modulate signaling through phosphorylation events . The rice ( Oryza sativa L ) XA21 receptor kinase is a key recognition and signaling determinant in the innate immune response . A yeast two-hybrid screen using the intracellular portion of XA21 , including the juxtamembrane ( JM ) and kinase domain as bait , identified a protein phosphatase 2C ( PP2C ) , called XA21 binding protein 15 ( XB15 ) . The interaction of XA21 and XB15 was confirmed in vitro and in vivo by glutathione-S-transferase ( GST ) pull-down and co-immunoprecipitation assays , respectively . XB15 fusion proteins purified from Escherichia coli and from transgenic rice carry PP2C activity . Autophosphorylated XA21 can be dephosphorylated by XB15 in a temporal and dosage-dependent manner . A serine residue in the XA21 JM domain is required for XB15 binding . Xb15 mutants display a severe cell death phenotype , induction of pathogenesis-related genes , and enhanced XA21-mediated resistance . Overexpression of Xb15 in an XA21 rice line compromises resistance to the bacterial pathogen Xanthomonas oryzae pv . oryzae . These results demonstrate that Xb15 encodes a PP2C that negatively regulates the XA21-mediated innate immune response .