Systemic acquired resistance (SAR) may be a whole-plant resistance response that happens following an earlier localized exposure to a pathogen. SAR is analogous to the innate system found in animals, and although there are many shared aspects between the 2 systems, it's thought to be a results of convergent evolution. Plants use pattern-recognition receptors to acknowledge conserved microbial signatures. This recognition triggers an immune reaction . Plants also carry immune receptors that recognize highly variable pathogen effectors, these include the NBS-LRR class of proteins. SAR is related to the induction of a good range of genes and therefore the activation of SAR requires the buildup of endogenous 2-hydroxybenzoic acid (SA). The pathogen-induced SA signal activates a molecular signal transduction pathway that's identified by a gene called NIM1, NPR1 or SAI1 (three names for an equivalent gene) within the model genetic system Arabidopsis thaliana .