Attenuation of riboflavin-induced resistance in response to Pst DC3000 in the mpk3 and mpk6 mutant.

(a) Expression of PR1 gene is compromised in the mpk3 and mpk6 mutant seedlings. 2-week-old WT and single mutant (mpk3, mpk6-2 and mpk6-3) seedlings were treated with water or riboflavin, and then inoculated with Pst DC3000 for 24 hours. The total RNAs were extracted at indicated times and analyzed for the expression of PR1 gene. Actin2 was used as an internal control. Control represents WT and single mutant seedlings were not treated with riboflavin and Pst DC3000. Different letters indicate statistically significant differences among the samples (P <0.05; Duncan’s multiple range tests). (b) Representative water- or riboflavin-treated leaves at 5 days after inoculation with Pst DC3000. The mpk3 and mpk6 mutants were significantly more susceptible to Pst DC3000 and failed to develop resistance by riboflavin. (c) Pathogen growth in WT and single mutant seedlings. Different letters indicate statistically significant differences among the samples (P <0.05; Duncan’s multiple range tests). The experiment was repeated three times with similar results.