Figure 2.
SA and PAD4 are critical for low-temperature enhancement of plant immunity. A, Growth curve of Pst DC3000 grown in Luria-Bertani liquid medium at 16°C and 22°C. Shown is the result from one experiment, and similar growth curves were observed for each temperature in a second experiment. B, Effect of temperature on the enzymatic activity of HopY1-CyaA. Shown are means ± sd of the amount of cAMP produced in reactions containing the lysate of Pst DC3000 carrying HopY1-CyaA with plant extracts at 16°C, 22°C, and 28°C. The plant extract was provided at a concentration of 0.5 or 1 μg μL−1. Data are means from seven biological repeats, and sd values are indicated by error bars. C, Effector translation at different temperatures. Shown is the amount of cAMP in leaves of temperature-acclimated plants syringe infiltrated with Pst DC3000 with AvrPto-CyaA, Pst DC3000 with HopY1-CyaA, or Pst DC3000 ΔhrcQ-hrcU with AvrPto-CyaA. Values were normalized by the total protein amount and the relative CyaA enzyme activity at the two temperatures. Data are means from seven biological repeats, and sd values are indicated by error bars. Asterisks indicate statistical significance based on Student’s t test (**, P < 0.01) of pairwise comparisons for each individual effector strain at 16°C versus 22°C. D, Growth of Pst DC3000 in wild-type Col-0 and cbf-1 and cbf-2 mutants measured at 4 dpi for 16°C and 3 dpi for 22°C. Values represent means ± sd (n = 3). cfu, Colony-forming units; FW, fresh weight. E and F, Growth of Pst DC3000 in the pad4 (E) and sid2 (F) mutants at 16°C, 22°C, and 28°C. The bacterial growth was measured at 4, 3, and 3 dpi at 16°C, 22°C, and 28°C, respectively. Values represent means ± sd (n = 3). Letters indicate statistically significant differences by ANOVA (P < 0.05). Similar results were obtained in three independent experiments, and shown is the result from one experiment with three biological repeats. G and H, MANOVA for pathogen growth in the mutant plants pad4 (G) and sid2 (H) compared with the wild-type plants at different temperatures. F, F test; MS, mean square; SS, square sum; Temp, temperature.