|全部作者||劉啟德 ,Berckx, F., Van Nguyen, T., Bandong, CM., Lin, HH., Yamanaka, T., Katayama, S., Wibberg, D., Blom, J., Kalinowski, J., Tateno, M., Simbahan, J., Liu, CT., Brachmann, A., Pawlowski, K.*|
|論文名稱||A tale of two lineages: how the strains of the earliest divergent symbiotic Frankia clade spread over the world|
|摘要||It is currently assumed that around 100 million years ago, the common ancestor to the Fabales, Fagales, Rosales and
Cucurbitales in Gondwana, developed a root nodule symbiosis with a nitrogen-fxing bacterium. The symbiotic trait
evolved frst in Frankia cluster-2; thus, strains belonging to this cluster are the best extant representatives of this origi‑
nal symbiont. Most cluster-2 strains could not be cultured to date, except for Frankia coriariae, and therefore many
aspects of the symbiosis are still elusive. Based on phylogenetics of cluster-2 metagenome-assembled genomes
(MAGs), it has been shown that the genomes of strains originating in Eurasia are highly conserved. These MAGs are
more closely related to Frankia cluster-2 in North America than to the single genome available thus far from the
southern hemisphere, i.e., from Papua New Guinea.
To unravel more biodiversity within Frankia cluster-2 and predict routes of dispersal from Gondwana, we sequenced
and analysed the MAGs of Frankia cluster-2 from Coriaria japonica and Coriaria intermedia growing in Japan, Taiwan
and the Philippines. Phylogenetic analyses indicate there is a clear split within Frankia cluster-2, separating a continen‑
tal from an island lineage. Presumably, these lineages already diverged in Gondwana.
Based on fossil data on the host plants, we propose that these two lineages dispersed via at least two routes. While
the continental lineage reached Eurasia together with their host plants via the Indian subcontinent, the island lineage
spread towards Japan with an unknown host plant.