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Contributions of the effector gene hopQ1-1 to differences in host range between Pseudomonas syringae pv. phaseolicola and P. syringae pv. tabaci.

ABSTRACT: To study the role of type III-secreted effectors in the host adaptation of the tobacco (Nicotiana sp.) pathogen Pseudomonas syringae pv. tabaci, a selection of seven strains was first characterized by multilocus sequence typing (MLST) to determine their phylogenetic affinity. MLST revealed that all strains represented a tight phylogenetic group and that the most closely related strain with a completely sequenced genome was the bean (Phaseolus vulgaris) pathogen P. syringae pv. phaseolicola 1448A. Using primers designed to 21 P. syringae pv. phaseolicola 1448A effector genes, it was determined that P. syringae pv. phaseolicola 1448A shared at least 10 effectors with all tested P. syringae pv. tabaci strains. Six of the 11 effectors that failed to amplify from P. syringae pv. tabaci strains were individually expressed in one P. syringae pv. tabaci strain. Although five effectors had no effect on phenotype, growth in planta and disease severity of the transgenic P. syringae pv. tabaci expressing hopQ1-1(Pph1448A) were significantly increased in bean, but reduced in tobacco. We conclude that hopQ1-1 has been retained in P. syringae pv. phaseolicola 1448A, as this effector suppresses immunity in bean, whereas hopQ1-1 is missing from P. syringae pv. tabaci strains because it triggers defences in Nicotiana spp. This provides evidence that fine-tuning effector repertoires during host adaptation lead to a concomitant reduction in virulence in non-host species.

SUBMITTER: Ferrante P

PROVIDER: S-EPMC6640246 | biostudies-literature | 2009 Nov

REPOSITORIES: biostudies-literature

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Contributions of the effector gene hopQ1-1 to differences in host range between Pseudomonas syringae pv. phaseolicola and P. syringae pv. tabaci.

Ferrante Patrizia P Clarke Christopher R CR Cavanaugh Keri A KA Michelmore Richard W RW Buonaurio Roberto R Vinatzer Boris A BA

Molecular plant pathology 20091101 6

To study the role of type III-secreted effectors in the host adaptation of the tobacco (Nicotiana sp.) pathogen Pseudomonas syringae pv. tabaci, a selection of seven strains was first characterized by multilocus sequence typing (MLST) to determine their phylogenetic affinity. MLST revealed that all strains represented a tight phylogenetic group and that the most closely related strain with a completely sequenced genome was the bean (Phaseolus vulgaris) pathogen P. syringae pv. phaseolicola 1448A ...[more]

PMID: 19849789

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Project description:BackgroundPseudomonas syringae pv. phaseolicola 1448a (P. syringae 1448a), the causative agent of bean halo blight, is a bacterium capable of occupying diverse biological niches. Under conditions of iron starvation P. syringae 1448a secretes siderophores for active uptake of iron. The primary siderophore of P. syringae 1448a is pyoverdine, a fluorescent molecule that is assembled from amino acid precursors by non-ribosomal peptide synthetase (NRPS) enzymes. Whereas other species of Pseudomonas often exhibit structural variations in the pyoverdine produced by different strains, all P. syringae pathovars previously tested have been found to make an identical pyoverdine molecule. P. syringae 1448a also appears to have the genetic potential to make two secondary siderophores, achromobactin and yersiniabactin, each of which has previously been detected in different P. syringae pathovars.ResultsFive putative pyoverdine NRPS genes in P. syringae 1448a were characterized in-silico and their role in pyoverdine biosynthesis was confirmed by gene knockout. Pyoverdine was purified from P. syringae 1448a and analyzed by MALDI-TOF and MS/MS spectroscopy. Peaks were detected corresponding to the expected sizes for the pyoverdine structure previously found in other P. syringae pathovars, but surprisingly P. syringae 1448a appears to also produce a variant pyoverdine species that has an additional 71 Da monomer incorporated into the peptide side chain. Creation of pyoverdine null mutants of P. syringae 1448a revealed that this strain also produces achromobactin as a temperature-regulated secondary siderophore, but does not appear to make yersiniabactin. Pyoverdine and achromobactin null mutants were characterized in regard to siderophore production, iron uptake, virulence and growth in iron limited conditions.ConclusionsThis study provides the first evidence of a P. syringae pathovar producing a side chain variant form of pyoverdine. We also describe novel IC₅₀ and liquid CAS assays to quantify the contribution of different siderophores across a range of iron starvation conditions, and show that although achromobactin has potential to contribute to fitness its contribution is masked by the presence of pyoverdine, which is a significantly more effective siderophore. Neither pyoverdine nor achromobactin appear to be required for P. syringae 1448a to cause bean halo blight, indicating that these siderophores are not promising targets for crop protection strategies.

Project description:Several reports have recently contributed to determine the effector inventory of the sequenced strain Pseudomonas syringae pv. phaseolicola (Pph) 1448a. However, the contribution to virulence of most of these effectors remains to be established. Genetic analysis of the contribution to virulence of individual P. syringae effectors has been traditionally hindered by the lack of phenotypes of the corresponding knockout mutants, largely attributed to a high degree of functional redundancy within their effector inventories. In support of this notion, effectors from Pseudomonas syringae pv. tomato (Pto) DC3000 have been classified into redundant effector groups (REGs), analysing virulence of polymutants in the model plant Nicotiana benthamiana. However, using competitive index (CI) as a virulence assay, we were able to establish the individual contribution of AvrPto1(Pto) (DC3000) to Pto DC3000 virulence in tomato, its natural host, even though typically, contribution to virulence of AvrPto1 is only shown in strains also lacking AvrPtoB (also called HopAB2), a member of its REG. This report raised the possibility that even effectors targeting the same defence signalling pathway may have an individual contribution to virulence, and pointed out to CI assays as the means to establish such a contribution for individual effectors. In this work, we have analysed the individual contribution to virulence of the majority of previously uncharacterised Pph 1448a effectors, by monitoring the development of disease symptoms and determining the CI of single knockout mutants at different stages of growth within bean, its natural host. Despite their potential functional redundancy, we have found individual contributions to virulence for six out of the fifteen effectors analysed. In addition, we have analysed the functional relationships between effectors displaying individual contribution to virulence, highlighting the diversity that these relationships may present, and the interest of analysing their functions within the context of the infection.

Project description:Mobile genetic elements are widespread in Pseudomonas syringae, and often associate with virulence genes. Genome reannotation of the model bean pathogen P. syringae pv. phaseolicola 1448A identified seventeen types of insertion sequences and two miniature inverted-repeat transposable elements (MITEs) with a biased distribution, representing 2.8% of the chromosome, 25.8% of the 132-kb virulence plasmid and 2.7% of the 52-kb plasmid. Employing an entrapment vector containing sacB, we estimated that transposition frequency oscillated between 2.6×10(-5) and 1.1×10(-6), depending on the clone, although it was stable for each clone after consecutive transfers in culture media. Transposition frequency was similar for bacteria grown in rich or minimal media, and from cells recovered from compatible and incompatible plant hosts, indicating that growth conditions do not influence transposition in strain 1448A. Most of the entrapped insertions contained a full-length IS801 element, with the remaining insertions corresponding to sequences smaller than any transposable element identified in strain 1448A, and collectively identified as miniature sequences. From these, fragments of 229, 360 and 679-nt of the right end of IS801 ended in a consensus tetranucleotide and likely resulted from one-ended transposition of IS801. An average 0.7% of the insertions analyzed consisted of IS801 carrying a fragment of variable size from gene PSPPH_0008/PSPPH_0017, showing that IS801 can mobilize DNA in vivo. Retrospective analysis of complete plasmids and genomes of P. syringae suggests, however, that most fragments of IS801 are likely the result of reorganizations rather than one-ended transpositions, and that this element might preferentially contribute to genome flexibility by generating homologous regions of recombination. A further miniature sequence previously found to affect host range specificity and virulence, designated MITEPsy1 (100-nt), represented an average 2.4% of the total number of insertions entrapped in sacB, demonstrating for the first time the mobilization of a MITE in bacteria.

Dataset Information

Contributions of the effector gene hopQ1-1 to differences in host range between Pseudomonas syringae pv. phaseolicola and P. syringae pv. tabaci.

Publications

Contributions of the effector gene hopQ1-1 to differences in host range between Pseudomonas syringae pv. phaseolicola and P. syringae pv. tabaci.

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