Objective 1: Generate functional EFR variants (EFR+) recognizing both elf18-Xac and elf18-CLas A number of strategies to engineer an EFR variant that recognized elf18-Clas were tested over the grant period, but none were successful. These strategies included PCR mutagenesis of EFR, screening of natural variants in an extensive Arabidopsis accession collection, creating targeted mutations based on the modeled interactions among elf18, EFR, and BAK1, and testing high-throughput selection strategies such as phage display and fluorescence activated cell sorting. Funding for this activity has ended and effort toward this objective has ceased. Objective 2. Generate functional XA21-EFR chimera (XA21-EFRchim) recognizing axYS22-Xac. This objective was completed and a manuscript describing the XA21-EFR chimera and the complementary EFR-XA21 chimera has been published (Holton et al., 2015, PLoS Pathogens 11, e1004602). Objective 3: Generate transgenic citrus plants expressing both EFR+ and XA21-EFRchim. Putative transgenic citrus plants have been generated for four constructs: EFR, EFR plus XA21, EFR plus XA21-EFRchim, and the empty vector pCAMBIA2201. To date, 174 Duncan grapefruit, 20 sweet orange, and 5 Carrizo citrange plants have been tranferred to soil, and PCR analysis is beginning to determine whether the intact transgenes are present.