Escalation in the host-pathogen arms race: A host resistance response corresponds to a heightened bacterial virulence response

PLoS Pathog. 2021 Jan 11;17(1):e1009175. doi: 10.1371/journal.ppat.1009175. eCollection 2021 Jan.

Abstract

The zig-zag model of host-pathogen interaction describes the relative strength of defense response across a spectrum of pathogen-induced plant phenotypes. A stronger defense response results in increased resistance. Here, we investigate the strength of pathogen virulence during disease and place these findings in the context of the zig-zag model. Xanthomonas vasicola pv. holcicola (Xvh) causes sorghum bacterial leaf streak. Despite being widespread, this disease has not been described in detail at the molecular level. We divided diverse sorghum genotypes into three groups based on disease symptoms: water-soaked lesions, red lesions, and resistance. Bacterial growth assays confirmed that these three phenotypes represent a range of resistance and susceptibility. To simultaneously reveal defense and virulence responses across the spectrum of disease phenotypes, we performed dual RNA-seq on Xvh-infected sorghum. Consistent with the zig-zag model, the expression of plant defense-related genes was strongest in the resistance interaction. Surprisingly, bacterial virulence genes related to the type III secretion system (T3SS) and type III effectors (T3Es) were also most highly expressed in the resistance interaction. This expression pattern was observed at multiple time points within the sorghum-Xvh pathosystem. Further, a similar expression pattern was observed in Arabidopsis infected with Pseudomonas syringae for effector-triggered immunity via AvrRps4 but not AvrRpt2. Specific metabolites were able to repress the Xvh virulence response in vitro and in planta suggesting a possible signaling mechanism. Taken together, these findings reveal multiple permutations of the continually evolving host-pathogen arms race from the perspective of host defense and pathogen virulence responses.

Publication types

  • Research Support, U.S. Gov't, Non-P.H.S.

MeSH terms

  • Gene Expression Regulation, Bacterial*
  • Gene Expression Regulation, Plant*
  • Host-Pathogen Interactions / immunology*
  • Plant Diseases / genetics
  • Plant Diseases / immunology
  • Plant Diseases / microbiology*
  • Sorghum / genetics
  • Sorghum / immunology
  • Sorghum / microbiology*
  • Transcriptome
  • Virulence*
  • Xanthomonas / genetics
  • Xanthomonas / immunology
  • Xanthomonas / pathogenicity*

Supplementary concepts

  • Xanthomonas vasicola

Grants and funding

The following funding supported this work: The United States Department of Energy grants DE-SC0018072 (RSB) and DE-SC0014395 (RSB and TCM); The United States Department of Energy Joint Genome Institute (KMV); and The United States Department of Energy Advanced Research Projects Agency-Energy (ARPA-E) award DE-AR0000594 (TCM). The views and opinions of authors expressed herein do not necessarily state or reflect those of the United States Government or any agency thereof. The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.