PhD defence: Downy mildew-associated microbiomes

All parts of the plant, both above and below ground, on the inside and on the outside, are colonized by a large diversity of microorganisms: the plant microbiome. Previous research has shown that above-ground infection of Arabidopsis thaliana by downy mildew (Hyaloperonospora arabidopsidis, Hpa) leads to changes in the soil and root microbiome. This altered microbiome is a legacy of the diseased plant that results in reduced Hpa infections in new generations of plants that grow in this soil.

In my dissertation, I mainly focused on the plant microbiome in the phyllosphere (above-ground parts of the plant), where downy mildew actually infects, to investigate whether these microbiomes are also 'modulated' in response to downy mildew infection. We also examine the link between phyllosphere microbiomes and the soil-borne legacy of the diseased plant.

We found that very specific disease-suppressing bacteria also accumulate in the phyllospheres of downy mildew-infected plants. Moreover, the specificity among the attracted microbes, in multiple independent systems, is many times higher than previously described. This gives us the possibility to further investigate these robust and specific interactions in order to uncover the molecular mechanisms underlying them.