UNCOUPLING PR GENE-EXPRESSION FROM NPR1 AND BACTERIAL-RESISTANCE - CHARACTERIZATION OF THE DOMINANT ARABIDOPSIS CPR6-1 MUTANT

In Arabidopsis, NPR1 mediates the salicylic acid (SA)-induced expressi on of pathogenesis-related (PR) genes and systemic acquired resistance (SAR), Here, we report the identification of another component, CPR6, that may function with NPR1 in regulating PR gene expression. The dom inant CPR6-1 mutant expresses the SA/NPR1-regulated PR genes (PR-1, BG L2, and PR-5) and displays enhanced resistance to Pseudomonas syringae pv maculicola ES4326 and Peronospora parasitica Noco2 in the absence of SAR induction. cpr6-1-induced PR gene expression is not suppressed in the cpr6-1 npr1-1 double mutant but is suppressed when SA is remove d by salicylate hydroxylase. Thus, constitutive PR gene expression in cpr6-1 requires SA but not NPR1. In addition, resistance to P. s. macu licola ES4326 is suppressed in the cpr6-1 npr1-1 double mutant, despit e expression of PR-1, BGL2, and PR-5, Resistance to P. s, maculicola E S4326 must therefore be accomplished through unidentified antibacteria l gene products that are regulated through NPR1. These results show th at CPR6 is an important regulator of multiple signal transduction path ways involved in plant defense.