The ability of plants to produce strigolactones affects rhizosphere community composition of fungi but not bacteria

Strigolactones are an important group of plant hormones. When released from roots, they act as signalling molecules that induce branching of arbuscular mycorrhizal hyphae. However, the extent to which they affect the rhizosphere microbiome is unknown. Filling this knowledge gap is important because the diversity and composition of the root-associated microbiome influence plant fitness. In this study, we hypothesised that strigolactone-producing plants harbour a different community of rhizosphere bacteria and fungi compared to plants whose strigolactone synthesis is impaired. To test this hypothesis, we compared the diversity of rhizosphere bacterial and fungal communities associated with wild-type Arabidopsis thaliana and a mutant impaired in the production of strigolactones due to a disruption of the MORE AXILLARY GROWTH 4 (MAX4) gene. Our results indicate that the plant's ability to produce strigolactone is significantly correlated with changes in the composition (beta diversity) of rhizosphere fungal but not bacterial communities. No differences in alpha diversity (richness and evenness) were observed for either bacterial or fungal communities between the rhizospheres of max4 and wild-type. Epicoccum nigrum, Penicillium, Fibulochlamys chilensis, Herpotrichiellaceae, Mycosphaerella and Mycosphaerellaceae were among the fungal taxa possibly attracted to or mostly influenced by strigolactones given that they were present at higher abundances in the rhizosphere of the wild-type compared to the mutant. Our study provides evidence that rhizosphere fungal diversity are more strongly affected than bacterial diversity by the plant's ability to produce strigolactones.