Obligate biotroph downy mildew consistently induces near-identical protective microbiomes in Arabidopsis thaliana.

Hyaloperonospora arabidopsidis (Hpa) is an obligately biotrophic downy mildew that is routinely cultured on Arabidopsis thaliana hosts that harbour complex microbiomes. We hypothesized that the culturing procedure proliferates Hpa-associated microbiota (HAM) in addition to the pathogen and exploited this model system to investigate which microorganisms consistently associate with Hpa. Using amplicon sequencing, we found nine bacterial sequence variants that are shared between at least three out of four Hpa cultures in the Netherlands and Germany and comprise 34% of the phyllosphere community of the infected plants.

Coumarin biosynthesis genes are required after foliar pathogen infection for the creation of a microbial soil-borne legacy that primes plants for SA-dependent defenses.

Plants deposit photosynthetically-fixed carbon in the rhizosphere, the thin soil layer directly around the root, thereby creating a hospitable environment for microbes. To manage the inhabitants of this nutrient-rich environment, plant roots exude and dynamically adjust microbe-attracting and -repelling compounds to stimulate specific members of the microbiome. Previously, we demonstrated that foliar infection of Arabidopsis thaliana by the biotrophic downy mildew pathogen Hyaloperonospora arabidopsidis (Hpa) leads to a disease-induced modification of the rhizosphere microbiome.

The Soil-Borne Identity and Microbiome-Assisted Agriculture: Looking Back to the Future.

Looking forward includes looking back every now and then. In 2007, David Weller looked back at 30 years of biocontrol of soil-borne pathogens by Pseudomonas and signified that the progress made over decades of research has provided a firm foundation to formulate current and future research questions. It has been recognized for more than a century that soil-borne microbes play a significant role in plant growth and health.

Root exudates drive the soil-borne legacy of aboveground pathogen infection.

Background: Plants are capable of building up beneficial rhizosphere communities as is evidenced by disease-suppressive soils. However, it is not known how and why soil bacterial communities are impacted by plant exposure to foliar pathogens and if such responses might improve plant performance in the presence of the pathogen. Here, we conditioned soil by growing multiple generations (five) of Arabidopsis thaliana inoculated aboveground with Pseudomonas syringae pv tomato (Pst) in the same soil.