The Pseudomonas syringae phytotoxin coronatine promotes virulence by overcoming salicylic acid‐dependent defences in Arabidopsis thaliana

Abstract

SUMMARY Successful pathogen infection likely involves the suppression of general antimicrobial host defences. One Pseudomonas syringae virulence factor proposed to act in this manner is coronatine (COR), a phytotoxin believed to function as an analogue of one or more jasmonates, a family of plant growth regulators. COR biosynthetic (COR(-)) mutants of P. syringae pv. tomato strain DC3000 exhibit reduced virulence on Arabidopsis thaliana and tomato. In the present study, three genetically and biochemically defined COR(-) mutants of DC3000 were used to explore potential effects of COR and its precursors, coronafacic acid (CFA) and coronamic acid (CMA), on defence signalling pathways in A. thaliana. Inoculation with wild-type DC3000 resulted in the accumulation of several jasmonate-responsive transcripts, whereas infection with a mutant strain that accumulates CFA, which is structurally similar to methyl jasmonate (MeJA), did not. Thus, COR, but not CFA, stimulates jasmonate signalling during P. syringae infection of A. thaliana. The ability of the COR(-) mutants to grow to high levels in planta was fully restored in A. thaliana lines deficient for salicylic acid (SA) accumulation. Although the COR(-) mutants grew to high levels in SA-deficient plants, disease symptoms were reduced in these plants. Collectively, these results indicate that COR is required both for overcoming or suppressing SA-dependent defences during growth in plant tissue and for normal disease symptom development in A. thaliana.

Arabidopsis MYC Transcription Factors Are the Target of Hormonal Salicylic Acid/Jasmonic Acid Cross Talk in Response to Pieris brassicae Egg Extract

“…However, attackers can also exploit this antagonism for their own benefit. For example, activation of the JA pathway by the biotroph pathogen Pseudomonas syringae pv tomato results in the inhibition of SA-dependent defenses through production of the virulence factor coronatine (COR), which is a JA-Ile analog (Brooks et al, 2005).…”

Microbe-Associated Molecular Patterns-Triggered Root Responses Mediate Beneficial Rhizobacterial Recruitment in Arabidopsis

“…Various lines of studies have shown that COR intervenes with the SA/JA antagonistic pathway to suppress a defense response in plants leading to susceptibility against Pst DC3000 (Brooks et al, 2005;Melotto et al, 2006). In contrast, a recent study showed that COR-induced suppression of plant defense is independent of SA-JA antagonism (Brooks et al, 2005;Katsir et al, 2008;Millet et al, 2010).…”

Cross Talk in Defense Signaling

“…For instance, virulent P. syringae bacteria produce coronatine that functions as a potent mimic of JA-Ile (Nomura et al, 2005). It is assumed that coronatine triggers hypersensitive induction of JA-Ile responses, resulting in suppression of effectual SA-dependent defenses through pathway cross talk, as well as enhanced growth of the pathogen (Zhao et al, 2003;Brooks et al, 2005;Cui et Doares et al, 1995;Spoel et al, 2003). However, Doares et al (1995) provided evidence that exogenous application of SA to tomato (Solanum lycopersicum) plants strongly inhibited the JA-induced expression of genes encoding proteinase inhibitors I and II, suggesting that SA also targets the JA pathway downstream of JA biosynthesis.…”