Immunity to bacterial pathogens is impaired in crk mutants.

(A) ROS production was enhanced in several crks compared to Col-0 wild type after elicitation with 100 nM flagellin (flg22) in 4 week-old leaves. Data show the percentage of the mean of the total RLU (relative light units) to Col-0 ± SE (n = 24). Asterisks indicate differences between crks and Col-0, statistical significance *P<0.05, **P<0.01 and ***P<0.001 (one-way ANOVA post hoc Dunnett). (B) A subset of crks was more susceptible to Pto DC3000 (spray infection of 2-week old seedlings at 10⁸ cfu ml^-1) compared to Col-0. Disease symptoms were scored 3 days post inoculation: 0, no symptom; 1, one symptomatic cotyledon; 2, two symptomatic cotyledons; 3, dead seedling. Results are means ± SE (n = 48). Asterisks indicate differences between crks and Col-0, statistical significance *P<0.05, **P<0.01 and ***P<0.001 (Mann-Whitney test, Benjamini-Hochberg correction for multiple comparisons). (C) Some crk mutants are impaired in stomatal closure after 2 h treatment with 10 mM flg22. Results are presented as mean of stomatal aperture ratio (width/length) after treatment compared to pre-treatment values in percentages ± SE (average number of stomata measured = 250). Asterisks indicate statistical significance between control treatment at *P<0.05, **P<0.01 and ***P<0.001 (linear model, single-step p-value adjustment). (D) Stomatal apertures were measured 2 h after chitin treatment. Stomatal closure is impaired in several crk mutants after treatment with chitin (1 g l^-1) for two hours (five selected mutants are shown). Results are means of % stomatal aperture ratio (width/length) after treatment ± SE (average number of stomata measured = 250). Asterisks indicate statistical significance between control treatment at *P<0.05, **P<0.01 and ***P<0.001 (linear model, single-step p-value adjustment). All experiments were repeated three times with similar results.