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A virus-induced gene silencing screen identifies a role for Thylakoid Formation1 in Pseudomonas syringae pv. tomato symptom development in tomato and Arabidopsis.

Wangdi T, Uppalapati SR, Nagaraj S, Ryu CM, Bender CL, Mysore KS

Plant Biology Division, The Samuel Roberts Noble Foundation, 2510 Sam Noble Parkway, Ardmore, Oklahoma 73401 USA; Department of Entomology and Plant Pathology, Oklahoma State University, Stillwater, OK 74078, USA.

Pseudomonas syringae pv. tomato DC3000 (Pst DC3000), which causes disease in tomato and Arabidopsis, produces coronatine (COR), a non-host specific phytotoxin. COR, which functions as a jasmonate mimic, is required for full virulence of Pst DC3000 and for the induction of chlorosis in host plants. Previous genetic screens based on insensitivity to COR and/or MeJA identified several potential targets for COR and MeJA. In this study, we utilized Nicotiana benthamiana and virus-induced gene silencing (VIGS) to individually reduce the expression of over 4,000 genes. The silenced lines of N. benthamiana were then screened for altered response to purified COR. Using this forward genetics approach several genes were identified with altered responses to COR. These were designated as altered COR response (ALC) genes. When silenced, one of the identified genes, ALC1, produced a hypersensitive/necrosis-like phenotype upon COR application in a Coronatine insensitive 1 (COI1) dependent manner. To understand the involvement of ALC1 during the Pst DC3000-host interaction, we used the nucleotide sequence of ALC1 and identified its ortholog in Arabidopsis (Thylakoid Formation1, THF1) and tomato (SlALC1). In pathogenicity assays performed on Arabidopsis thf1 mutant and SlALC1-silenced tomato plants, Pst DC3000 induced accelerated coalescing necrotic lesions. Furthermore, we showed that COR affects ALC1 localization in chloroplast in a COI1-depenendent manner. In conclusion, our results show that VIGS-based forward genetic screen has potential to identify new players in COR signaling and disease associated necrotic cell death.

Published 16 November 2009 in Plant Physiol.
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