The rhizosphere microbiome and host plant glucosinolates exhibit feedback cycles in Brassica rapa

Paru dans Molecular ecology

Dewolf, E., Brock, M.T., Calder, W.J., Kliebenstein, D.J., Katz, E., Li, B.H., Morrison, H.G., Maignien, L., Weinig, C.

The rhizosphere microbiome influences  many aspects of plant fitness, including production of secondary  compounds and defence against insect herbivores. Plants also modulate the composition of the microbial community in the rhizosphere via secretion of root exudates. We tested both the effect of the rhizosphere microbiome on plant  raits, and host plant effects on rhizosphere microbes using recombinant inbred lines (RILs) of Brassica rapa that differ in production of glucosinolates (GLS), secondary metabolites that contribute to defence against insect herbivores. First, we investigated the effect of genetic variation in GLS production on the composi-tion of the rhizosphere microbiome. Using a Bayesian  Dirichlet-multinomial regres-sion model (DMBVS), we identified both negative and positive associations between bacteria from six genera and the concentration of five GLS compounds produced in plant roots. Additionally, we tested the effects of microbial inoculation (an intact vs. disrupted soil microbiome) on GLS production and insect damage in these RILs. We found a significant microbial treatment × genotype interaction, in which total GLS was higher in the intact relative to the disrupted microbiome treatment in some RILs. However, despite differences in GLS production between microbial treatments, we observed no difference in insect damage between treatments. Together, these results provide evidence for a full feedback cycle of plant–microbe interactions mediated by GLS; that is, GLS compounds produced by the host plant “feed-down” to influence rhizosphere microbial community and rhizosphere microbes “feed-up” to influence GLS production.