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Publications of the Week

A Genome-Wide Screen Identifies Genes in Rhizosphere-Associated Pseudomonas Required to Evade Plant Defenses

By November 22, 2018No Comments

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This week we profile a recent publication in mBio from the laboratory of
Dr. Cara Haney (pictured, centre) at the Michael Smith Laboratories.

Can you provide a brief overview of your lab’s current research focus?

The Haney lab investigates the genetic factors that regulate assembly of host-associated microbial communities, or microbiomes. We use genetic and molecular approaches, combined with high-throughput assays, and next-generation sequencing, to probe the interface of the rhizosphere microbiome with the model plant Arabidopsis. We are interested in both basic mechanisms that regulate host-microbiome interactions, and learning about the plant microbiome to improve agricultural sustainability through use of microbes.

What is the significance of the findings in this publication?

Plant-associated microbial communities improve plant health by helping plants defend against pathogens and helping with nutrient uptake. Like those microbes that colonize the human gut, plant root, or “rhizosphere” communities must evade plant immunity and use host-derived nutrients. To determine how members of the plant microbiome evades plant immunity, we use a model system consisting of the beneficial bacterium Pseudomonas fluorescens and the model host Arabidopsis thaliana. Using this system, we performed a genome-wide screening, using a technique called “Tn-Seq” to identify bacterial genes required to evade the plant immune system. We identified 231 genes in this strain that either positively affected fitness in the rhizosphere of wild-type plants, or negatively affected fitness in the rhizosphere of immunocompromised plants. Out of the 231 genes, we focused on two specific genes, morA and spuC, and the role they play in evading the host immune system. We found that both morA and spuC prevent hyperbiofilm formation by bacteria and help the bacteria avoid triggering an immune response. We found that spuC plays a critical role in the metabolism of a polyamine called putrescine, a small organic molecule. We found that putrescine promotes biofilm formation suggesting that putrescine may be a plant-derived signal that can trigger a lifestyle change in bacteria.

What are the next steps for this research?

Evasion or suppression of the plant immune system is essential for commensals to colonize their plant hosts. This works suggests that host-derived polaymines, including putrescine or derivatives, might be involved in recruiting members of the microbiome. We are exploring how bacteria sense host-derived polyamines, and how bacteria sense and process this signal in a way that allows them to successfully colonize a host.

This research was funded by:

This work was supported by NSERC Discovery Grant, Canada Foundation for Innovation, and Canada Research Chair grants, Toteston & Fund for Medical Discovery Fellowship, the Gordon and Betty Moore Foundation through Grant to the Life Sciences Research Foundation (LSRF), Simons Foundation Grant to the LSRF, and NSERC URSA.

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