Identification and cloning of a negative regulator of systemic acquired resistance, SNlI1, through a screen for suppressors of npr1-1

Systemic acquired resistance (SAR) is a plant immune response induced after a local infection by necrotizing pathogens. The Arabidopsis NPR1 gene is a positive regulator of SAR, essential for transducing the SAR signal salicy lic acid (SA). Mutations in the NPR1 gene abolish the SA-induced expression of pathogenesis-related (PR) genes and resistance to pathogens. To identif y additional regulators of SAR, we screened for suppressors of npr1-1. In t he npr1-1 background, the sni1 (suppressor of npr1-1, inducible 1) mutant s hows near wild-type levels of PR1 expression and resistance to pathogens af ter induction. Restoration of SAR in npr1-1 by the recessive sni1 mutation indicates that wild-type SNI1 may function as a negative regulator of SAR. We cloned the SNI1 gene and found that it encodes a leucine-rich nuclear pr otein.