Figure 3.

Phosphorylation Specificity between CDPKs and MAPKs.

(A) CPK18 phosphorylated tobacco WIPK and SIPK, rice MPK6, and Arabidopsis MPK3 but hardly phosphorylated rice MPK4. The autophosphoryaltion of MAPKs was blocked by the mutation of essential residues (SIPK-KR and WIPK-KR) or by adding the MAPK inhibitor SB202190 (right panel; Os MPK6 and At MPK3), except for rice MPK4, which had barely detectable autophosphorylation. At, Arabidopsis; MW, molecular mass marker; Os, rice. Bacterial protein contaminants copurified with MAPKs are indicated with asterisks on the Coomassie Brilliant Blue (CBB)–stained gels.

(B) Rice CPK4 phosphorylated MPK5KR but CPK7 did not. The common CDPK substrate Histone III (Histone type III-S) was used as a positive control to show GST-CPK7 activity. The asterisk indicates a protein contaminant in Histone III.