Expression of extra-cellular levansucrase in Pseudomonas syringae is controlled by the in planta fitness-promoting metabolic repressor HexR

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.

Lscβ and lscγ, two novel levansucrases of Pseudomonas syringae pv. actinidiae biovar 3, the causal agent of bacterial canker of kiwifruit, show different enzymatic properties

“…Interestingly the presence of a likely non-functional lscA gene has also been described in P. syringae pv. glycinea PG 4180 due to an altered upstream region which does not seem to allow its expression [46]. Therefore, the levan production in Psa3 appears to relay on the sole lscβ and lscγ alleles.…”

“…Levan production is a common feature among members of the Pssc, which is useful for discriminating its members from other fluorescent plant pathogenic Pseudomonas when grown on sucrose rich media [1,29]. However the biological functions of levan for this vast group of plant pathogens is poorly understood and different hypotheses are currently under investigation: it can form a "barrier" on the bacterial cell that prevents recognition and consequent active responses by the host, as well as it can be a "side product" of the active release of glucose, the major carbon source for P. syringae, from sucrose, an abundant storage sugar present in the plant apoplast [19,46]. Here, we report the description of the enzymatic activity of two novel lscs, lscβ and lscγ, of Psa3 the causal agent of the current pandemic of canker disease of kiwifruit.…”

“…Nnevertheless under in vivo conditions the multiplication of the pathogen under this pH value seems plausible. It is well known that P. syringae exploits stomatal openings and wounds to entry in plants apoplast which presents an acidic pH (from 5.0 to 5.5) and thereafter a complex sequence of events, mediated by the infection process, activates a K + /H + plant-borne efflux and influx, which increases the apoplastic pH to 7.5 [46]. Indeed Atkinson in 1987 [50] demonstrated that P. syringae pv.…”

Complete genome assembly of the levan‐positive strain PVFi1 of Pseudomonas savastanoi pv. savastanoi isolated from olive knots in Central Italy

“…In the pathovar glycinea several regulatory elements have been proved to be necessary for the gene expression and enzymatic activity Hettwer et al ., 1998; Li and Ullrich, 2001; Srivastava et al ., 2012; Khandekar et al ., 2014; Mehmood et al ., 2015; Abdallah et al ., 2016), which have been also found in our PVFi1 strain: (i) the PAPE region with the com gene; (ii) the transcriptional start site; (iii) the N‐terminal sequence of 48 bp; (iv) the hexose metabolism repressor HexR ; (v) the prophage‐borne transcriptional regulator lscR ; (vi) the enzyme catalytic sites, defined as block I, block II and block III; and (vii) the stem‐loop region for translation termination. This in silico reconstructed region of 5072 bp when blasted appeared to be more related to Pseudomonas syringae pv.…”

The Immunomodulatory Properties of β-2,6 Fructans: A Comprehensive Review

“…In terms of its biological role, microbial levan acts as a constituent of biofilm matrices in some bacteria [ 31 , 80 ] and has also been suggested to contribute towards plant pathogen fitness and virulence [ 48 , 81 , 82 ]. Further, in soil-resident bacteria, levan has been shown to aid in tolerance to salt and desiccation as well formation of cell aggregates on abiotic surfaces suggesting a role for levan in environment adaptions of bacteria under high osmotic stress and in biofilm formation [ 80 ].…”