Enhanced in planta Fitness through Adaptive Mutations in EfpR, a Dual Regulator of Virulence and Metabolic Functions in the Plant Pathogen Ralstonia solanacearum

PLoS Pathog. 2016 Dec 2;12(12):e1006044. doi: 10.1371/journal.ppat.1006044. eCollection 2016 Dec.

Abstract

Experimental evolution of the plant pathogen Ralstonia solanacearum, where bacteria were maintained on plant lineages for more than 300 generations, revealed that several independent single mutations in the efpR gene from populations propagated on beans were associated with fitness gain on bean. In the present work, novel allelic efpR variants were isolated from populations propagated on other plant species, thus suggesting that mutations in efpR were not solely associated to a fitness gain on bean, but also on additional hosts. A transcriptomic profiling and phenotypic characterization of the efpR deleted mutant showed that EfpR acts as a global catabolic repressor, directly or indirectly down-regulating the expression of multiple metabolic pathways. EfpR also controls virulence traits such as exopolysaccharide production, swimming and twitching motilities and deletion of efpR leads to reduced virulence on tomato plants after soil drenching inoculation. We studied the impact of the single mutations that occurred in efpR during experimental evolution and found that these allelic mutants displayed phenotypic characteristics similar to the deletion mutant, although not behaving as complete loss-of-function mutants. These adaptive mutations therefore strongly affected the function of efpR, leading to an expanded metabolic versatility that should benefit to the evolved clones. Altogether, these results indicated that EfpR is a novel central player of the R. solanacearum virulence regulatory network. Independent mutations therefore appeared during experimental evolution in the evolved clones, on a crucial node of this network, to favor adaptation to host vascular tissues through regulatory and metabolic rewiring.

MeSH terms

  • Gene Expression Profiling
  • Genes, Plant / genetics*
  • Mutation
  • Plant Diseases / microbiology*
  • Polymerase Chain Reaction
  • Ralstonia solanacearum / genetics*
  • Ralstonia solanacearum / metabolism*
  • Ralstonia solanacearum / pathogenicity*
  • Virulence / genetics*
  • Virulence Factors / metabolism

Substances

  • Virulence Factors

Grant support

AG, SG, XB and JG received funding from ‘Institut National de la Recherche Agronomique’ (INRA), Plant Health Division (SPE) (http://www.spe.inra.fr/) (AAP SPE 2015 grant). All authors received funding from the French Laboratory of Excellence project TULIP (https://www.labex-tulip.fr/) (ANR-10-LABX-41; ANR-11-IDEX-0002-02). AP was funded by INRA-SPE and the ‘Région Midi-Pyrénées’ (http://www.regionlrmp.fr/) (No. 15000183). RP was supported by EMBO (http://www.embo.org) (Long-Term Fellowship ALTF 1627-2011), Marie Curie Actions (http://ec.europa.eu/research/mariecurieactions/) (EMBOCOFUND2010, GA-2010-267146), and European Research Council (https://erc.europa.eu/) (ERC-StG336808 project VariWhim). The funders had no role in study design, data collection and analysis, decision to publish, or preparation of the manuscript.