Figure 3.

agb1-2 suppresses cell death in transgenic plants overexpressing SOBIR1 and compromised PAMP-triggered immunity. A, Morphology of the wild type, 35S-SOBIR1 transgenic line number 2 (SOBIR1 OX-2; Gao et al., 2009), and agb1-2 carrying the 35S-SOBIR1 transgene from line number 2 (agb1-2 SOBIR1 OX-2). Plants were grown on soil at 23°C and photographed approximately 3 weeks after planting. B, Trypan blue staining of the indicated genotypes. Plants were grown at 23°C for 2 weeks on one-half-strength MS plates. C to E, flg22-induced (C), elf18-induced (D), or chitin-induced (E) resistance to P. syringae pv tomato DC3000 in the wild type, gpa1-3 (SALK_066823), agb1-2, and a transgenic line expressing AGB1 under its own promoter in agb1-2 background (agb1/AGB1). Plants were pretreated with the indicated PAMPs (+) or water (−) 1 d before infiltration with P. syringae pv tomato DC3000 (OD₆₀₀ = 0.001). Bacterial titers on day 3 are shown. Error bars represent sds from means of six measurements. Asterisks above the bars indicate significant difference between samples treated with or without the indicated elicitors (*P < 0.01). Statistical differences among the elicitor-treated samples are labeled with different letters (P < 0.01). F to H, Oxidative burst triggered by flg22 (F), elf18 (G), or chitin (H) in the indicated genotypes. Leaf slices of 4-week-old plants were treated with 1 μm flg22, 1 μm elf18, or 200 μg mL^–1 chitin, and ROS was subsequently measured. Error bars represent sds from means of eight samples. I, Activation of MPK3 and MPK6 in the wild type and agb1-2 by flg22. Two-week-old seedlings grown on one-half-strength MS medium were treated with or without 1 μm flg22. Phosphorylated MPK3 and MPK6 were detected by western blot using an anti-Erk1/2 antibody specific for the phosphorylated MAPKs. mpk3 and mpk6 knockout mutants were included as controls. J, Activation of MPK4 in the wild type and agb1 mutants by flg22. Two-week-old seedlings grown on one-half-strength MS medium were treated with or without 1 μm flg22. MPK4 was immunoprecipitated from total protein extracts using anti-MPK4 antibodies (Sigma) and assayed for its kinase activity (autoradiograph) using MBP as the substrate. WT, Wild type. [See online article for color version of this figure.]