Activation of RPP 5 locus R genes causes similar phenotypes in bal , cpr1 , and snc1 mutants. (A) Organization of the RPP5 locus in the Columbia haplotype. The R genes and a related TIR-NBS gene, At4g16990, are indicated by open arrows while non-R-genes are indicated by filled arrows. R genes that are up-regulated in all three mutants are indicated by filled upward arrowheads. Additional R genes up-regulated in the bal variant are indicated by open upward arrowheads (Additional File 1 and Data Not Shown); the expression of these genes has not yet been determined for cpr1 and snc1. Transposon-related sequences are not indicated. Cen: centromere. (B) Phenotypes of 3-week old bal, cpr1, and snc1 homozygous mutants along with a wild-type plant. Scale bar: 1 cm.