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Abstract:
Plants recruit microbial communities from the soil in which they germinate. Our understanding
of the recruitment process and the factors affecting it is still limited for most
microbial taxa. We analysed several factors potentially affecting root microbiome
structure – the importance of geographic location of natural populations, the microbiome
of native seeds as putative source of colonization and the effect of a plant’s response to
UVB exposure on root colonization of highly abundant species. The microbiome of
Nicotiana attenuata seeds was determined by a culture-dependent and culture-independent
approach, and the root microbiome of natural N. attenuata populations from five
different locations was analysed using 454-pyrosequencing. To specifically address the
influence of UVB light on root colonization by Deinococcus, a genus abundant and
consistently present in N. attenuata roots, transgenic lines impaired in UVB perception
(irUVR8) and response (irCHAL) were investigated in a microcosm experiment with/
without UVB supplementation using a synthetic bacterial community. The seed
microbiome analysis indicated that N. attenuata seeds are sterile. Alpha and beta diversities
of native root bacterial communities differed significantly between soil and root,
while location had only a significant effect on the fungal but not the bacterial root communities.
With UVB supplementation, root colonization of Deinococcus increased in
wild type, but decreased in irUVR8 and irCHAL plants compared to nontreated plants.
Our results suggest that N. attenuata recruits a core root microbiome exclusively from
soil, with fungal root colonization being less selective than bacterial colonization. Root
colonization by Deinococcus depends on the plant’s response to UVB.
