One of the main plant defence mechanisms is the Systemic Acquired Resistance (SAR) mediated by Salicylic Acid (SA). This is a heightened and broad-spectrum immune response initiated by the exposure to pathogens, inducing resistance not only in the infected site, but also throughout the entire plant. It was demonstrated that plant immune system can be regulated by two classes of SA receptors: NONEXPRESSOR OF PR GENES 1 (NPR1) and NPR1-LIKE PROTEIN 3 and 4 (NPR3/NPR4). While NPR1 is required for SA-induction followed by the expression of pathogenesis-related (PR) protein and resistance against pathogens, NPR3/NPR4 serve as transcriptional co-repressors of SA-responsive genes.