Paladin, a tyrosine phosphatase-like protein, is required for XA21-mediated immunity in rice

XA21 encodes a rice immune receptor that confers robust resistance to most strains of the Gram-negative bacterium Xanthomonas oryzae pv.oryzae(Xoo).XA21-mediated immunity is triggered by recognition of a small protein called RaxX-sY(required for activation of XA21-mediated immunity X,tyrosine-sulfated)secreted by Xoo.To identify components regulating XA21-mediated immunity,we generated and screened a mutant population of fast-neutron-mutagenized rice expressing Ubi:Myc-XA21 for those susceptible to Xoo.Here,we report the characterization of one of these rice mutants,named sxi2(suppressor of XA21-mediated immunity-2).Whole-genome sequencing revealed that sxi2 carries a deletion of the PALADIN(PALD)gene encoding a protein with three putative protein tyrosine phosphatase-like domains(PTP-A,-B,and-C).Expression of PALD in the sxi2 genetic background was sufficient to complement the susceptible phenotype,which requires the catalytic cysteine of the PTP-A active site to restore resistance.PALD coimmunoprecipitated with the full-length XA21 protein,whose levels are positively regulated by the presence of the PALD transgene.Furthermore,we foundd that sxi2 retains many hallmarks of XA21-mediated immunity,similar to the wild type.These results reveal that PALD,a previously uncharacterized class of phosphatase,functions in rice innate immunity,and suggest that the conserved cysteine in the PTP-A domain of PALD is required for its immune function.