Extracts from cultures of Pseudomonas fluorescens induce systemic resistance to biotic pathogens in Arabidopsis thaliana

Can rhizobacteria in the soil help plants' systemic resistance to infection?

Pathogenic organisms are the cause of many plant diseases and these can often lead to reduced productivity and crop yield. As a result, the interactions between pathogens and plants have been studied extensively. Yet some pathogens can in fact be beneficial to plants, conferring increased tolerance to stress and improving overall plant health. One such group of pathogens is the plant growth promoting rhizobacteria (PGPR) that improve the ability of the plant to cope with cellular oxidative stress. This phenomenon is termed induced systemic resistance (ISR). Interest in PGPR has spiked recently with their potential applications to sustainable agriculture (without pesticides or agrochemicals) becoming clear. A handful of metabolites from various bacterial genera have now been identified as metabolic elicitors of ISR in plants, yet a true understanding of this response at a molecular level is still lacking.

The image shows one of the 12-well plastic plates with Arabidopsis thaliana plants that have been sprayed with the pathogen Pseudomonas syringae DC3000. This plate is a negative control that was used to check the infection symptoms of the pathogen. Leafs have big chlorosis spots. Image credit: Martin-Rivilla et al.

In a new study published in AoBP, Martin-Rivilla et al. evaluated the ability of various PGPR metabolites to induce systemic resistance to the pathogenic Pseudomonas syringae in the model plant Arabidopsis thaliana. The authors used three different organic solvents to extract metabolic molecules of the beneficial PGPR bacterial strain Pseudomonas fluorescens N 21.4. All extracted molecules showed some form of plant protective activity but the molecules extracted using the organic solvent n-hexane were the most efficient. These n-hexane extracts were able to activate the two defensive pathways of the plant immune system (the salicylic acid signalling pathway and the jasmonic acid/ethylene signalling pathway) and all the enzymes responsible for reducing the oxidative stress that plants experience when they are subjected to some kind of attack. Whilst further studies are required to chemically identify the elicitors excreted by P. fluorescens; the authors believe their use as biotechnological inoculants to improve plant resistance to stress is a promising possibility.

Researcher highlight

Helena Martin-Rivilla obtained a Bachelor’s degree in Biology and then focused her career in the field of Plant Sciences by studying a Master of Applied Plant Biology.  In 2016, Helena started a PhD in Pharmacy in the San Pablo CEU University within the research group of Biotechnology of Plant-Microbiome Interaction. She is currently finishing her thesis on the use of PGPRs (Plant Growth Promoting Rhizobacteria) for the induction of secondary metabolism to improve the defensive capacity and the nutritional quality of blackberry. She also works in the Environment Government Area of the Madrid City Council in improving waste management.

Helena is interested in the study of new and more ecofriendly biotechnological tools to improve crop quality and plant resistance to biotic and abiotic stress to ensure food security worldwide.

Further reading

Martin-Rivilla, H., Garcia-Villaraco, A., Ramos-Solano, B., Gutierrez-Mañero, F. J., & Lucas, J. A. (2019). Extracts from cultures of Pseudomonas fluorescens induce defensive patterns of gene expression and enzyme activity while depressing visible injury and reactive oxygen species in Arabidopsis thaliana challenged with pathogenic Pseudomonas syringae. AoB PLANTS, 11(5). https://doi.org/10.1093/aobpla/plz049