Unique and unifying themes in the mechanisms regulating the expression of the Arabidopsis thaliana PR-1 and Solanum tuberosum PR-10a inducible defense genes

Arabidopsis is a model plant used to study disease resistance; Solanum tuberosum or potato is a crop species. Both plants possess inducible defense mechanisms that are deployed upon recognition of pathogen invasion. Transcriptional reprogramming is crucial to the activation of defense responses. The Pathogenesis-Related (PR) genes are activated in these defense programs. Expression of Arabidopsis PR-1 and potato PR-10a serve as markers for the deployment of defense responses in these plants.;The PR-10a is activated in response to pathogen invasion, wounding and elicitor treatment. PR-10a induction requires recruitment of the Whirly 1 (Why1) activator to the promoter. This locus is also negatively regulated by the silencer element binding factor (SEBF).;We established that both the PR-1 and PR-10a are occupied by repressors under non-inducing conditions. TGA2 was found to be a constitutive resident and repressor of PR-1, which mediates repression by forming an oligomeric complex on the promoter. The DNA-binding activity of this oligomer required the TGA2 N-terminus (NT).;Under resting conditions we determined that the PR-10a is bound by a repressosome containing SEBF and curiously the activator Pto interacting protein 4 (Pti4). In the context of this repressosome, SEBF is responsible for PR-10a binding, yet recruitment of SEBF to this locus required the Pti4.;PR-1 expression indicates induction of systemic acquired resistance (SAR). Activation of SAR requires accumulation of salicylic acid (SA), in addition to the interaction of the non-expressor of pathogenesis-related genes 1 (NPR1), with the TGA transcription factors.;We also showed that PR-1and PR-10a are activated by different means. In PR-1 activation the NPR1 NT domain alleviates TGA2-mediated repression by interacting with the TGA2 NT. TGA2 remains at the PR-1 but adopts a dimeric conformation and forms an enhanceosome with NPR1. In contrast, the PR-10a is activated by evicting the repressosome and recruiting Why1 to the promoter.;These results advance our understanding of the mechanisms regulating PR-1 and PR-10a expression under resting and inducing conditions. This study also revealed that the means of regulation for related genes can differ greatly between model and crop species, which has important implications for the field of translational biology.