Figure 6.

The CPK18-MPK5 Pathway Negatively Regulates Plant Immunity.

(A) CPK18-RI plants exhibited enhanced resistance to M. oryzae. Lesion size, lesion number, and relative fungal amount were compared between the wild type and CPK18-RI lines 6 d after fungal infection. Asterisks indicate statistically significant differences (*P < 0.05, **P < 0.01, Student’s t test). The results are shown as means ± se (n = 3 biological repeats).

(B) Rice disease symptoms caused by M. oryzae strain 70-15 in the wild type and CPK18-RI lines. The photograph was taken 6 d after inoculation.

(C) RT-qPCR analysis shows that the expression of defense-related genes (Chitinase, Hin1, PR5, and PR10) was increased in CPK18-RI and MPK5-RI plants in comparison with the wild type (**P < 0.01, Student’s t test). The data are shown as means ± sd (n = 3).

(D) and (E) The phosphorylation-mimic mutant MPK5DD (T14D-T32D) exhibited stronger ability to repress PR5 and Hin1 promoter activity than did MPK5 in rice protoplast reporter assays. A plasmid containing PR5_pro:GUS or Hin1_pro:GUS was cotransfected with FLAG-tagged MPK5, MPK5DD, or empty vector (CK) (D). Promoter activities were determined based on the relative GUS activity. The P values from Student’s t test are shown in the plot. The results are presented as means ± sd (n = 5). Protein levels of MPK5 and MPK5DD in rice protoplasts were examined by immunoblotting (WB) using anti-FLAG antibody (E). Equal protein loading is indicated by Coomassie Brilliant Blue (CBB) staining.

[See online article for color version of this figure.]