Plant bacterial pathogens survive in soil by changing their genetic expression pattern

• Plant-infecting bacteria are able to survive in soil in between disease outbreaks.

• CRAG researchers have found how an important plant pathogen, Ralstonia solanacearum, activates certain types of genes to be able to survive in the harsh soil conditions.

• This knowledge is crucial to control pathogen dissemination and prevent crop plagues.

Bacterial pathogens which infect plants exhibit a remarkable ability to persist and thrive in diverse environments. These populations of bacteria outside their hosts are the ones responsible for dissemination and potential disease outbreaks. However, most of the studies on plant pathogenic bacteria have been focused solely on their interaction with their living host.

In this article published in the journal PLOS Pathogens and lead by Marc Valls, UB researcher at CRAG, researchers have elucidated how the plant pathogen Ralstonia solanacearum is able to survive in two key environmental habitats that it occupies: water and soil.

Ralstonia solenacearum is a soil bacterium with devastating effects on many solanaceous crops such as tomato, in which produces the bacterial wilt (also known as brown rot in potato and granville wilt in tobacco). Due to rise in temperatures caused by the present climate crisis, this tropical bacteria is now dangerously spreading to other countries. 

Adaptation to the environment

In this work, CRAG researchers have used Ralstonia as a model to investigate pathogen adaptation to water and soil, and have compared this information with the gene expression of the pathogen in the plant. By using high-throughput genetic analyses, CRAG researchers have found a distinct pattern of gene expression in each of the environments. In water, gene expression pattern is similar to that encountered during late infection stages in plants, in late xylem colonization. 

In contrast, in the soil this bacteria activates a series of very different and specific genes necessary to adapt and survive in this unique environment. Importantly, these genes are not used by the bacterium during plant infection, confirming the ability of this pathogen to adapt to this specific phase of its life cycle, in the absence of the natural host.

Aromatic compounds as nutrients

The genes that are activated in the soil phase are mainly involved in the adaptation to the increased oxidative stress in the soil but also, and more importantly, related to the degradation of aromatic compounds. Aromatic compounds are abundant in soil due to the presence of for example antimicrobials, pollutants or derivatives of wood degradation, and this finding suggests that they could be used as nutrients by pathogens.

″The next step will be to identify the exact aromatic compounds used by this pathogen to be able to control its population in soil″, says Marc Valls, lead author of the work.

For the experiments, researchers used real soil samples extracted from fields of land in the Vallès Oriental region in Catalonia (Santa Eulàlia de Ronçana), which had to be treated beforehand to kill soil microorganisms and to remove the previously present genetic material that would otherwise interfere with the analysis.

Since it has been reported that bacterial pathogens can survive up to five years in soil, understanding the mechanisms enabling their transition between habitats is crucial to control dissemination and potential disease outbreaks of plant pathogens.

Reference Article

de Pedro-Jové R, Corral J, Rocafort M, Puigvert M, Azam FL, Vandecaveye A, et al. Gene expression changes throughout the life cycle allow a bacterial plant pathogen to persist in diverse environmental habitats. PLoS Pathog 202; 19(12): e1011888. https://doi.org/10.1371/journal.ppat.1011888

About the authors and funding of the study

This research was funded by grant MCIN/AEI/PID2019-108595RB-I00 to M.V. and N.S.C. The Center for Research in Agricultural genomics is supported by the ‘Severo Ochoa Programme for Centres Centers of Excellence in R&D’ (CEX2019-000917 funded by MCIN/AEI/ 10.13039/501100011033) and by the CERCA Program of the Generalitat de Catalunya. R.P.J. received FPU Fellowship (FPU2018-03285) funded by Ministerio de Universidades and FI Fellowship (2019 FI_B 00461) from the Secretaria d’Universitats i Recerca del Departament d’Empresa i Coneixement de la Generalitat de Catalunya and the co-funding of the European Social Fund (ESF—″ESF is investing in your future″) from the European Union. J. C was the recipient of a Margarita Salas 2021 Fellowship (Contract ID:675711) at Autonomous University of Barcelona (UAB) funded by Ministerio de Universidades and by ″European Union NextGenerationEU/PRTR. The funders did not play any role in the study design, data collection, analysis, decision to publish or preparation of the manuscript.