CorR Regulates Multiple Components of Virulence in Pseudomonas syringae pv. tomato DC3000

Abstract

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 (sigmaL) 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 sigmaL, 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.

Abscisic Acid-Induced Resistance against the Brown Spot Pathogen Cochliobolus miyabeanus in Rice Involves MAP Kinase-Mediated Repression of Ethylene Signaling

“…For instance, some P. syringae pathovars have shown an ability to synthesize ET both in vitro and in planta from Met through the 2-keto-4-methylthiobutyric acid pathway (Weingart et al, 2001). This ability, together with the production of the JA mimic coronatine and auxins by the same microorganisms, is assumed to contribute to hormonal saturation and consequent circumvention of effectual defenses (Cui et al, 2005;Sreedharan et al, 2006). More recently, Ralstonia solanacearum has been seen to produce ET by means of the HrpG regulon (Valls et al, 2006).…”

Pseudomonas syringae pv. tomato DC3000 CmaL (PSPTO4723), a DUF1330 Family Member, Is Needed To Produce l - allo -Isoleucine, a Precursor for the Phytotoxin Coronatine

“…CFA and CMA are produced independently and can be supplied exogenously to restore COR production to corresponding P. syringae pv. tomato DC3000 mutants (6,22). The cfa and cma operons, respectively, responsible for the production of these moieties are separated by 26 kb in P. syringae pv.…”

“…tomato DC3000, and it is noteworthy that PSPTO4723 is only 8.8 kb downstream from cmaU, the last gene in the cma operon (21,23). The cma genes are linked with the corR, corS, and corP genes, encoding a modified two-component regulator system that coregulates the cfa and cma operons (21,22). Current uncertainties about COR production in P. syringae pv.…”

“…tomato DC3000 response regulator CorR regulates the production of both CFA and CMA (22). The corR gene is preceded by hopAQ1, which encodes an unconfirmed candidate type III effector and is itself preceded by a HrpL-responsive promoter (22,24,25).…”

“…tomato DC3000 response regulator CorR regulates the production of both CFA and CMA (22). The corR gene is preceded by hopAQ1, which encodes an unconfirmed candidate type III effector and is itself preceded by a HrpL-responsive promoter (22,24,25). HrpL is an extracytoplasmic function (ECF) class alternative sigma factor that regulates the expression of the hrp-hrc T3SS genes and the hop genes (26,27).…”