NPR1 and infection: To determine the role of SA production, we challenged sid2‐1 plants, which are impaired in their ability to produce SA upon pathogen infection (Wildermuth, Dewdney, Wu, & Ausubel, 2001), npr1‐1 plants, defective in the NPR1/NIM1 protein function that regulates SA‐dependent defence gene induction (Cao et al., 1994), and NahG plants, which convert SA into catechol (Lawton et al., 1995).