DOI: 10.1094/MPMI-19-0768

CorR Regulates Multiple Components of Virulence in Pseudomonas syringae pv. tomato DC3000. Aswathy Sreedharan (1), Alejandro Penaloza-Vazquez (1), Barbara N. Kunkel (2), and Carol L. Bender (1). (1) Department of Entomology and Plant Pathology, 127 Noble Research Center, Oklahoma State University, Stillwater 74078, U.S.A.; (2) Department of Biology, Washington University, St. Louis, MO 63130, U.S.A. MPMI 19:768-779. Submitted 1 December 2005. Accepted 19 February 2006. Copyright 2006 The American Phytopathological Society.

The phytotoxin coronatine (COR) is produced by various pathovars of Pseudomonas syringae, including P. syringae pv. tomato DC3000, which is pathogenic on crucifers and tomato, and P. syringae pv. glycinea PG4180, a soybean pathogen. The COR molecule contains two distinct components, coronafacic acid (CFA) and coronamic acid (CMA), which are intermediates in the COR biosynthetic pathway. In P. syringae pv. tomato DC3000, it is not clear whether corR, which encodes a response regulator, positively regulates CFA and CMA synthesis as it does in P. syringae pv. glycinea PG4180. In this study, a corR mutant of P. syringae pv. tomato DC3000 was constructed and was shown to be defective in the production of COR, CFA, and CMA. Furthermore, disease severity was greatly reduced in tomato plants inoculated with the corR mutant compared with wild-type P. syringae pv. tomato DC3000. We also showed that a mutation in hrpL, which encodes an alternate RNA polymerase sigma factor (sigma(^L)) required for the expression of genes encoding components of the type III secretion system, abrogated production of COR in P. syringae pv. tomato DC3000. The presence of a potential hrp box, the recognition site for sigma(^L), upstream of corR suggested that corR might be regulated by hrpL. This was confirmed in reverse-transcription polymerase chain reaction experiments showing that the upstream effector gene holPtoAA, which was associated with the hrp box, was cotranscribed with corR. Furthermore, studies also were conducted to investigate whether mutations in corR had effects on the expression of hrpL. The corR mutant of P. syringae pv. tomato DC3000 showed both a reduction and delay in the expression of hrpL and was impaired in its ability to elicit a hypersensitive response on Nicotiana benthamiana. A putative CorR-binding site was identified upstream of hrpL, and gel shift studies confirmed the binding of CorR to this region. These results indicate that corR directly impacts the expression of the hrp regulon in P. syringae.

This online article contains two supplemental figures. Figure S1 shows Nicotiana benthamiana infiltrated with Pseudomonas syringae pv. tomato DC3000, corR and hrpL mutants, and water. Figure S2 shows the alignment of the CorR-binding site upstream of the cfl gene in Pseudomonas syringae pv. glycinea PG4180.

Supplemental Table S1 lists fluorogenic LUX primer pairs used for quantitative real-time polymerase chain reaction (RT-qPCR).