Genome-sequencing of the obligate symbiotic, Mycoplasma-related endobacteria of arbuscular mycorrhizal fungi to uncover their function and coevolution.

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Arbuscular mycorrhizal fungi (AMF), symbionts of land plants for >400 million years (My), are known to host in their cytoplasm Gram-positive endobacteria traditionally called bacterium-like organisms (BLOs). Recently, we could show that 16S rDNA sequences of AMF-BLOs (from highly diverse AMF lineages) all fall in a >400 My old monophyletic clade in the class Mollicutes. Despite the fact that the uncultivable BLOs must play an important, maybe organelle-like role in AMF, their function is thus far unknown. In this project, we aim to achieve a full sequencing of the genomes of BLOs to founder understanding their functioning in the important AM symbiosis. Within a single AMF spore BLOs are genetically polymorphic. To explore and annotate their metagenome and individual genome sequences, we will use two well defined AMF isolates and combine metagenomics, single cell sorting, whole genome amplification and new sequencing technologies. This will provide comprehensive insights into the capacities and environmental and evolutionary adaptations of BLOs. The unprecedented data regarding these elusive bacteria and their hosts potentially are highly interesting also for applied, agricultural aspects. We anticipate that BLO genome sequence information may reveal essential or advantageous metabolic pathways, antibiotics-synthesis or -resistance, putative significance for AM evolution (e.g., by horizontal gene transfer), and several unforeseeable aspects, like hints for effector secretion.