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A horizontally acquired expansin gene increases virulence of the emerging plant pathogen Erwinia tracheiphila.

ABSTRACT: Erwinia tracheiphila is a bacterial plant pathogen that causes a fatal wilt infection in some cucurbit crop plants. Wilt symptoms are thought to be caused by systemic bacterial colonization through xylem that impedes sap flow. However, the genetic determinants of within-plant movement are unknown for this pathogen species. Here, we find that E. tracheiphila has horizontally acquired an operon with a microbial expansin (exlx) gene adjacent to a glycoside hydrolase family 5 (gh5) gene. Plant inoculation experiments with deletion mutants in the individual genes (?exlx and ?gh5) and the full operon (?exlx-gh5) resulted in decreased severity of wilt symptoms, decreased mortality rate, and impaired systemic colonization compared to the Wt strain. Co-inoculation experiments with Wt and ?exlx-gh5 rescued the movement defect of the mutant strain, suggesting that expansin and GH5 function extracellularly. Together, these results show that expansin-GH5 contributes to systemic movement through xylem, leading to rapid wilt symptom development and higher rates of plant death. The presence of expansin genes in diverse species of bacterial and fungal wilt-inducing pathogens suggests that microbial expansin proteins may be an under-appreciated virulence factor for many pathogen species.

SUBMITTER: Rocha J

PROVIDER: S-EPMC7729394 | biostudies-literature | 2020 Dec

REPOSITORIES: biostudies-literature

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A horizontally acquired expansin gene increases virulence of the emerging plant pathogen Erwinia tracheiphila.

Rocha Jorge J Shapiro Lori R LR Kolter Roberto R

Scientific reports 20201210 1

Erwinia tracheiphila is a bacterial plant pathogen that causes a fatal wilt infection in some cucurbit crop plants. Wilt symptoms are thought to be caused by systemic bacterial colonization through xylem that impedes sap flow. However, the genetic determinants of within-plant movement are unknown for this pathogen species. Here, we find that E. tracheiphila has horizontally acquired an operon with a microbial expansin (exlx) gene adjacent to a glycoside hydrolase family 5 (gh5) gene. Plant inocu ...[more]

PMID: 33303810

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Project description:Erwinia tracheiphila is the causal agent of bacterial wilt of cucurbits, an economically important phytopathogen affecting an economically important phytopathogen affecting few cultivated Cucurbitaceae few cultivated Cucurbitaceae host plant species in temperate eastern North America. However, essentially nothing is known about E. tracheiphila population structure or genetic diversity. To address this shortcoming, a representative collection of 88 E. tracheiphila isolates was gathered from throughout its geographic range, and their genomes were sequenced. Phylogenomic analysis revealed three genetic clusters with distinct hrpT3SS virulence gene repertoires, host plant association patterns, and geographic distributions. Low genetic heterogeneity within each cluster suggests a recent population bottleneck followed by population expansion. We showed that in the field and greenhouse, cucumber (Cucumis sativus), which was introduced to North America by early Spanish conquistadors, is the most susceptible host plant species and the only species susceptible to isolates from all three lineages. The establishment of large agricultural populations of highly susceptible C. sativus in temperate eastern North America may have facilitated the original emergence of E. tracheiphila into cucurbit agroecosystems, and this introduced plant species may now be acting as a highly susceptible reservoir host. Our findings have broad implications for agricultural sustainability by drawing attention to how worldwide crop plant movement, agricultural intensification, and locally unique environments may affect the emergence, evolution, and epidemic persistence of virulent microbial pathogens.IMPORTANCEErwinia tracheiphila is a virulent phytopathogen that infects two genera of cucurbit crop plants, Cucurbita spp. (pumpkin and squash) and Cucumis spp. (muskmelon and cucumber). One of the unusual ecological traits of this pathogen is that it is limited to temperate eastern North America. Here, we complete the first large-scale sequencing of an E. tracheiphila isolate collection. From phylogenomic, comparative genomic, and empirical analyses, we find that introduced Cucumis spp. crop plants are driving the diversification of E. tracheiphila into multiple lineages. Together, the results from this study show that locally unique biotic (plant population) and abiotic (climate) conditions can drive the evolutionary trajectories of locally endemic pathogens in unexpected ways.

Dataset Information

A horizontally acquired expansin gene increases virulence of the emerging plant pathogen Erwinia tracheiphila.

Publications

A horizontally acquired expansin gene increases virulence of the emerging plant pathogen Erwinia tracheiphila.

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