Abstract
The nonhost-specific phytotoxin coronatine (COR) produced by several pathovars of Pseudomonas syringae functions as a jasmonic acid-isoleucine (JA-Ile) mimic and contributes to disease development by suppressing plant defense responses and inducing reactive oxygen species in chloroplast. It has been shown that the F-box protein CORONATINE INSENSITIVE 1 (COI1) is the receptor for COR and JA-Ile. JASMONATE ZIM DOMAIN (JAZ) proteins act as negative regulators for JA signaling in Arabidopsis. However, the physiological significance of JAZ proteins in P. syringae disease development and nonhost pathogen-induced hypersensitive response (HR) cell death is not completely understood. In this study, we identified JAZ genes from tomato, a host plant for P. syringae pv. tomato DC3000 (Pst DC3000), and examined their expression profiles in response to COR and pathogens. Most JAZ genes were induced by COR treatment or inoculation with COR-producing Pst DC3000, but not by the COR-defective mutant DB29. Tomato SlJAZ2, SlJAZ6 and SlJAZ7 interacted with SlCOI1 in a COR-dependent manner. Using virus-induced gene silencing (VIGS), we demonstrated that SlJAZ2, SlJAZ6 and SlJAZ7 have no effect on COR-induced chlorosis in tomato and Nicotiana benthamiana. However, SlJAZ2-, SlJAZ6- and SlJAZ7-silenced tomato plants showed enhanced disease-associated cell death to Pst DC3000. Furthermore, we found delayed HR cell death in response to the nonhost pathogen Pst T1 or a pathogen-associated molecular pattern (PAMP), INF1, in SlJAZ2- and SlJAZ6-silenced N. benthamiana. These results suggest that tomato JAZ proteins regulate the progression of cell death during host and nonhost interactions.
Highlights
Several pathovars of Pseudomonas syringae, including pvs. atropurpurea, glycinea, maculicola, morsprunorum and tomato, produce the nonhost-specific phytotoxin coronatine (COR)
Tomato SlJAZ Genes were Upregulated by Coronatine and Pseudomonas syringae pv. tomato DC3000
We demonstrated that 12 SlJAZ genes were induced by Pst DC3000, but only seven of 12 JASMONATE ZIM DOMAIN (JAZ) genes were upregulated in response to COR
Summary
Several pathovars of Pseudomonas syringae, including pvs. atropurpurea, glycinea, maculicola, morsprunorum and tomato, produce the nonhost-specific phytotoxin coronatine (COR). Atropurpurea, glycinea, maculicola, morsprunorum and tomato, produce the nonhost-specific phytotoxin coronatine (COR). COR is a polyketide formed by the coupling of coronafacic acid (CFA) and coronamic acid (CMA) through an amide bond [1]. COR functions as a structural and functional analog of a phytohormone, jasmonic acid-isoleucine (JA-Ile) [2,3,4]. The F-box protein CORONATINE INSENSITIVE 1 (COI1) is known to be required for COR and JA signaling in tomato and Arabidopsis [1,2,5,6]. COR activates the JA-signaling pathway by mimicking JA-Ile in Arabidopsis and tomato and thereby functions to suppress the stomata-mediated and/or SA-mediated defenses, allowing bacteria to grow to higher densities in planta [6,7,8,9]. The physiological significance of COR-induced disease development is not completely understood
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