Discussion
Although Pseudomonas syringae infection in plants is actively inhibited by the endogenous salicylic acid (SA) of host origin, a successful infection is still established because the bacterium secretes coronatine, an effector molecule. Which one of the following best describes the mode of action of coronatine?
Answer: D
Coronatine is a structural analogue of jasmonic acid (JA), which activates JA signaling to inhibit SA response.
Coronatine closely mimics the active hormone jasmonoyl-isoleucine (JA-Ile). It binds the COI1-JAZ co-receptor, triggers degradation of the JAZ repressors and switches on jasmonate signalling. Because the JA and SA pathways antagonise each other, activating JA signalling suppresses the SA-dependent defences that would otherwise restrict Pseudomonas syringae, and coronatine also reopens stomata for bacterial entry.
Coronatine does not act as an SA analogue or by directly blocking SA biosynthesis, and it does not work by raising the plant's own JA synthesis; it is itself the JA mimic.
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