Abstract
BackgroundPseudomonas syringae pv. glycinea PG4180 causes bacterial blight on soybean plants and enters the leaf tissue through stomata or open wounds, where it encounters a sucrose-rich milieu. Sucrose is utilized by invading bacteria via the secreted enzyme, levansucrase (Lsc), liberating glucose and forming the polyfructan levan. P. syringae PG4180 possesses two functional lsc alleles transcribed at virulence-promoting low temperatures.ResultsWe hypothesized that transcription of lsc is controlled by the hexose metabolism repressor, HexR, since potential HexR binding sites were identified upstream of both lsc genes. A hexR mutant of PG4180 was significantly growth-impaired when incubated with sucrose or glucose as sole carbon source, but exhibited wild type growth when arabinose was provided. Analyses of lsc expression resulted in higher transcript and protein levels in the hexR mutant as compared to the wild type. The hexR mutant’s ability to multiply in planta was reduced. HexR did not seem to impact hrp gene expression as evidenced by the hexR mutant’s unaltered hypersensitive response in tobacco and its unmodified protein secretion pattern as compared to the wild type under hrp-inducing conditions.ConclusionsOur data suggested a co-regulation of genes involved in extra-cellular sugar acquisition with those involved in intra-cellular energy-providing metabolic pathways in P. syringae.Electronic supplementary materialThe online version of this article (doi:10.1186/s12866-015-0349-0) contains supplementary material, which is available to authorized users.
Highlights
Pseudomonas syringae pv. glycinea PG4180 causes bacterial blight on soybean plants and enters the leaf tissue through stomata or open wounds, where it encounters a sucrose-rich milieu
Generation and genotypic characterization of the P. syringae hexR mutant T del Castillo, E Duque and JL Ramos [23] and A Daddaoua, T Krell and JL Ramos [22] had previously shown that genes encoding enzymes of the phosphorylative branch and the ED pathway of glucose catabolism in P. putida were regulated by the hexose metabolism repressor, HexR
In order to investigate the impact of HexR on expression of lscB and lscC genes, a hexR-deficient mutant of P. syringae PG4180 was generated by insertion of a kanamycin resistance cassette in the hexR gene as a result of homologous recombination
Summary
Pseudomonas syringae pv. glycinea PG4180 causes bacterial blight on soybean plants and enters the leaf tissue through stomata or open wounds, where it encounters a sucrose-rich milieu. When plant-borne sucrose is present, the soybeaninfecting bacterial blight pathogen, Pseudomonas syringae pv. A complex sequence of events mediated by injection of bacterial hypersensitive reaction and pathogenicity (Hrp) effector proteins into plant cells [11] activates plant-borne K+ efflux and H+ influx, which increases the apoplastic pH from 5.5 to 7.5 [12]. This high extra-cellular pH induces efflux of the dominant photo assimilate, sucrose, from plant cells [12]. Apoplastic sucrose ranging in concentrations from 20 μM to 1–5 mM is hydrolyzed by either plant-borne invertases or by extracellular microbial enzymes, e.g. Lsc [13,14]
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