Gene expression and phytohormone levels in the asymptomatic and symptomatic phases of infection in potato tubers inoculated with Dickeya solani

PLoS One. 2022 Aug 29;17(8):e0273481. doi: 10.1371/journal.pone.0273481. eCollection 2022.

Abstract

Dickeya solani is a soft rot bacterium with high virulence. In potato, D. solani, like the other potato-infecting soft rot bacteria, causes rotting and wilting of the stems and rotting of tubers in the field and in storage. Latent, asymptomatic infections of potato tubers are common in harvested tubers, and if the storage conditions are not optimal, the latent infection turns into active rotting. We characterized potato gene expression in artificially inoculated tubers in nonsymptomatic, early infections 1 and 24 hours post-inoculation (hpi) and compared the results to the response in symptomatic tuber tissue 1 week (168 hpi) later with RNA-Seq. In the beginning of the infection, potato tubers expressed genes involved in the detection of the bacterium through pathogen-associated molecular patterns (PAMPs), which induced genes involved in PAMPs-triggered immunity, resistance, production of pathogenesis-related proteins, ROS, secondary metabolites and salicylic acid (SA) and jasmonic acid (JA) biosynthesis and signaling genes. In the symptomatic tuber tissue one week later, the PAMPs-triggered gene expression was downregulated, whereas primary metabolism was affected, most likely leading to free sugars fueling plant defense but possibly also aiding the growth of the pathogen. In the symptomatic tubers, pectic enzymes and cell wall-based defenses were activated. Measurement of hormone production revealed increased SA concentration and almost no JA in the asymptomatic tubers at the beginning of the infection and high level of JA and reduced SA in the symptomatic tubers one week later. These findings suggest that potato tubers rely on different defense strategies in the different phases of D. solani infection even when the infection takes place in fully susceptible plants incubated in conditions leading to rotting. These results support the idea that D. solani is a biotroph rather than a true necrotroph.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Dickeya
  • Enterobacteriaceae / genetics
  • Gene Expression
  • Pathogen-Associated Molecular Pattern Molecules
  • Plant Diseases / genetics
  • Plant Diseases / microbiology
  • Plant Growth Regulators
  • Salicylic Acid
  • Solanum tuberosum* / microbiology

Substances

  • Pathogen-Associated Molecular Pattern Molecules
  • Plant Growth Regulators
  • Salicylic Acid

Supplementary concepts

  • Dickeya solani

Grants and funding

MP was supported by Ministry of Agriculture and Forestry of Finland, grant 567/312/2011 (mmm.fi/en/frontpage). Metabolomics unit (NS) is supported by Biocenter Finland (biocenter.fi) and Helsinki Institute of Life Science HiLIFE (https://www2.helsinki.fi/en/helsinki-institute-of-life-science). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript. Open access funded by Helsinki University Library.