Arbuscular mycorrhizal fungi reduce growth and infect roots of the non-host plant Arabidopsis thaliana

The arbuscular mycorrhizal (AM) symbiosis is widespread
throughout the plant kingdom and important for plant nutrition
and ecosystem functioning. Nonetheless, most terrestrial
ecosystems also contain a considerable number of nonmycorrhizal
plants. The interaction of such non-host plants
with AM fungi (AMF) is still poorly understood. Here, in
three complementary experiments, we investigated whether
the non-mycorrhizal plant Arabidopsis thaliana, the model
organism for plant molecular biology and genetics, interacts
with AMF. We grew A. thaliana alone or together with a
mycorrhizal host species (either Trifolium pratense or
Lolium multiflorum) in the presence or absence of the AMF
Rhizophagus irregularis. Plants were grown in a dualcompartment
system with a hyphal mesh separating roots of
A. thaliana from roots of the host species, avoiding direct
root competition. The host plants in the system ensured the
presence of an active AM fungal network. AM fungal networks
caused growth depressions in A. thaliana of more
than 50% which were not observed in the absence of host
plants. Microscopy analyses revealed that R. irregularis supported
by a host plant was capable of infecting A. thaliana
root tissues (up to 43% of root length colonized), but no
arbuscules were observed. The results reveal high susceptibility
of A. thaliana to R. irregularis, suggesting that
A. thaliana is a suitable model plant to study non-host/AMF
interactions and the biological basis of AM incompatibility.