Takahashi, D. | bioRxiv Science

bioRxiv2020

Updated phylogeny and sequence features of MreB from the Wall-less bacteria Spiropaslma

Spiroplasma are wall-less bacteria which belong to the phylum Tenericutes that evolved from Firmicutes including Bacillus subtilis. Spiroplasma swim by a mechanism unrelated to widespread bacterial motilities, such as flagellar motility, and caused by helicity switching with kinks traveling along the helical cell body. The swimming force is likely generated by five classes of bacterial actin homolog MreBs (SMreBs 1-5) involved in the helical bone structure. We analyzed sequences of SMreBs to clarify their phylogeny and sequence features. The maximum likelihood method based on around 5,000 MreB sequences showed that the phylogenetic tree was divided into several radiations. SMreBs formed a clade adjacent to the radiation of MreBH, an MreB isoform of Firmicutes. Sequence comparisons of SMreBs and Bacillus MreBs were also performed to clarify the features of SMreB. Catalytic glutamic acid and threonine were substituted to aspartic acid and lysine, respectively, in SMreB3. In SMreBs 2 and 4, amino acids involved in inter- and intra-protofilament interactions were significantly different from those in Bacillus MreBs. A membrane-binding region was not identified in most SMreBs 1 and 4 unlike many walled-bacterial MreBs. SMreB5 had a significantly longer C-terminal region than the other MreBs, which possibly forms a protein-protein interaction. These features may support the functions responsible for the unique mechanism of Spiroplasma swimming.

bioinformatics↗

bioRxiv2020

Geographic and subsequent biotic isolations led to a diversity anomaly of Heterotropa (Aristolochiaceae) in insular versus continental regions of the Sino-Japanese Floristic Region

The Sino-Japanese Floristic Region is highly diverse with respect to temperate plants. However, the reasons for this diversity are poorly understood because most studies have only considered geographic isolation caused by climatic oscillations. Heterotropa (genus Asarum; Aristolochiaceae) diverges here and shows high species diversity in insular systems (63 species) compared to continental areas (25 species). Heterotropa shows low dispersal ability with small distribution ranges, implying diversification by geographic events, and high floral diversity, implying pollinator-mediated diversification. To reveal how abiotic and biotic factors have shaped the diversity anomaly of Heterotropa, we conducted phylogenetic analysis using ddRAD-seq and chloroplast genome datasets including 79 species, estimation of floral trait evolution, and comparison of isolation factors within clades based on distribution range and floral trait analysis. Phylogenetic analysis indicates that Heterotropa originated in mainland China and expanded to the Japanese Archipelago in the Miocene, and the major clades almost correspond to geographic distributions. Floral traits evolved repeatedly in the tip nodes within the clades. Although the major clades include a high proportion of species pairs showing isolation by floral traits, there are no conditional relationships between two isolation factors, indicating that most species pairs with floral trait isolation are distributed allopatrically. The repeated exposure and submergence of land-bridges caused by climatic oscillations would have led to significant population fragmentation in insular systems. Thus, the diversity anomaly of Heterotropa would have resulted from geographic and climatic events during the Miocene, while subsequent repeated floral trait evolution would have followed geographic isolation during the Pleistocene.

plant biology↗