Role of coronatine in the virulence of Pseudomonas syringae pv. tomato DC3000 on edible brassicas

Abstract

Scope and Method of Study: The phytotoxin coronatine (COR), produced by different strains of Pseudomonas syringae has two moieties: coronamic acid (CMA) and coronafacic acid (CFA). The bacterium P. syringae pv. tomato DC3000 is pathogenic on tomato, Arabidopsis and edible species of brassicas. This study is focused on understanding the roles of COR and its components in the bacterial virulence on two major cultivated brassicas, collard and turnip. Furthermore, defense gene expression in these two plants in response to COR-defective biosynthetic mutants as well as the purified toxin and its components were investigated.

Findings and Conclusions: COR contributed to the virulence of Pst DC3000 in both collard and turnip by contributing to the symptoms in both plants and bacterial multiplication in turnip. Gene expression studies showed that COR stimulated the activation of CORI1 and LOX2 genes and suppression of PR-1 gene in both plants. The treatment of turnip with AK7E2 (CFA+ CMA-) resulted in chlorosis, expression of CORI1 and LOX2 genes and PR-1 suppression; suggesting the role of CFA in defense modulation in this plant. The exogenous application of purified COR also induced chlorophyll degradation and JA activation on both plants, whereas the CFA component induced JA-mediated defense in turnip. The activation of the jasmonic acid (JA) pathway by COR may be a part of the general virulence strategy of the pathogen. The results of this study suggest that CFA component has some role in the interaction of Pst DC3000 with turnip but not collard.