Jihoon Jo1, Seok-Wan Choi1, Minho Seo1, and Hwan Su Yoon1
1 Department of Biological Sciences, Sungkyunkwan University, Suwon, South Korea
The genus Vaucheria is a grass-like yellow-green algal group (Xanthophyceae, Ochrophyta) inhabiting various aquatic environments such as freshwater streams, lakes, salt marshes, and seashores. Interestingly, this genus is the unique group having diverse sexual reproduction modes, from hermaphroditic, monoecious, to dioecious, while other Xanthophyceae only have the asexual mode. Although their physiological and sexual diversification, just a few systematics studies had been conducted using several phylogenetic-marker genes, and there is no genomic application. In this study, we collected 20 Vaucheria species (or strains), and sequenced organelle genomes (i.e., plastids and mitochondria) with an asexual ancestor Asterosiphon dichotomus to explore the phylogenetic relationships underlying the evolution of this fascinating algal group. We also performed comparative genome analyses to investigate structural variation and genetic repertoires. As a result, we constructed complete plastid and mitochondrial genomes of all species and inferred a more reliable evolutionary history correlating with habitat adaptation and sexual reproduction mode. We also found a unique mitochondrial genome structure by identifying large inverted-repeat regions that had never been reported in the Ochrophyta lineage. This study will help provide a genomic view for understanding the evolutionary biology of the Vaucheria and furthermore Xanthophyceae.