PAD4 was found to be required for modulating SA accumulation in pathogen-infected plants (Zhou et al., 1998; Jirage et al., 1999; Rietz et al., 2011), and for systemic acquired resistance, an inducible defense mechanism that increases resistance against subsequent infections in plants that previously experienced a localized infection (Shah and Zeier, 2013). Here, PADI4 is linked to infection.