AtAO3 negatively regulates systemic acquired resistance (SAR). Relative transcript accumulation of (a) PR1 gene, (b) PR2 gene, (c) G3DPH, and (d) AZI genes analyzed using quantitative real-time PCR (qPCR) in systemic leaves after Pst DC3000 (avrB) inoculation. The Y-axis of panels (a) and (b) was interrupted to clarify the small values. The expression was normalized against constitutively expressed Actin. Error bars represent ±SE (n = 3). Significant differences are represented by different letters (p ≤ 0.05) calculated by DMRT.