The Plant Immunity Regulating F-Box Protein Supports Plastid Function in Absence of Pathogens.

The mutant ( of was isolated in a genetic screening approach for mutants with defects in chloroplast-to-nucleus redox signaling. It has an atypically low activation status of the 2-Cys peroxiredoxin-A promoter in the seedling stage. shows wildtype-like germination, seedling development and greening, but slower growth and reduced biomass in the rosette stage. Mapping of the casual mutation revealed that carries a single nucleotide polymorphism in the gene encoding (At4g12560), leading to a premature stop codon. CPR1 is known as a repressor of pathogen signaling and regulator of microtubule organization. Allelism of and revealed a function of CPR1 in chloroplast stress protection. Expression studies in pathogen signaling mutants demonstrated that CPR1-mediated activation of genes for photosynthesis and chloroplast antioxidant protection is, in contrast to activation of pathogen responses, regulated independently from PAD4-controlled salicylic acid (SA) accumulation. We conclude that the support of plastid function is a basic, SA-independent function of CPR1.