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Diatom biodiversity and speciation revealed by comparative analysis of mitochondrial genomes
  • Nansheng Chen
Nansheng Chen

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Diatoms (Bacillariophyta) constitute one of the most diverse and ecologically significant groups of phytoplankton, comprising at least 100,000 species in three classes Bacillariophyceae, Mediophyceae, and Coscinodiscophyceae. Nevertheless, diatom biodiversity and evolutionary history remain elusive due to limited genomic information. Here, we constructed complete mitochondrial genomes (mtDNAs) of 15 diatom species including five Coscinodiscophyceae species (Guinardia delicatula, Guinardia striata, Stephanopyxis turris, Paralia sulcata, and Actinocyclus curvatulus), four Mediophyceae species (Hemiaulus sinensis, Odontella aurita var. minima, Lithodesmioides polymorpha, Helicotheca tamesis), and six Bacillariophyceae species (Nitzschia ovalis, Nitzschia sp., Nitzschia traheaformis, Cylindrotheca closterium, Haslea tsukamotoi, Pleurosigma intermedium). Comparative analysis of these mtDNAs, together with diatom mtDNAs that have been published, revealed extensive genome rearrangement events, gene duplications, gene losses, and gains and losses of introns. Duplication of cox1 was discovered for the first time in diatoms in Nitzschia traheaformis and Haslea tsukamotoi. Phylogenetic analysis of 68 Bacillariophyta species revealed that species of the genus Nitzschia were so diverse that they could represent multiple genera. mtDNAs showed extensive genome rearrangement events including translocations and/or inversion at the class level, while high conservation at the order level. Molecular dating analysis revealed that the three diatom classes split 100 Mya and many diatom species appeared 50 Mya. More mtDNAs of diatoms representing different orders will play great dividends to explore biodiversity and speciation of diatoms in different ecological regions.