Coronatine and salicylic acid: the battle between Arabidopsis and Pseudomonas for phytohormone control

SUMMARY The phytotoxin coronatine is a jasmonate mimic produced by Pseudomonas syringae pv. tomato (Pst). Coronatine acts as a virulence factor in Arabidopsis and mutants insensitive to coronatine are resistant to Pst and have higher levels of salicylic acid (SA). In this work we used the SA-deficient lines NahG and sid2-2 to determine if coronatine acts directly as a virulence factor or indirectly by SA suppression. Using coronatine-deficient Pst mutants we demonstrated that the lack of coronatine compromises Pst virulence in both wild-type and SA-deficient Arabidopsis. Thus, the action of coronatine is not due to SA suppression. Rather, SA-independent jasmonate-responses are the most likely mechanism for its action.