To further understand the trends in the evolution of mitochondrial genomes (mitogenomes or mtDNAs) in the Ulvophyceae, the mitogenomes of two separate thalli of Ulva pertusa were sequenced. Two U. pertusa mitogenomes (Up1 and Up2) were 69,333 bp and 64,602 bp in length. These mitogenomes shared two ribosomal RNAs (rRNAs), 28 transfer RNAs (tRNAs), 29 protein-coding genes, and 12 open reading frames. The 4.7 kb difference in size was attributed to variation in intron content and tandem repeat regions. A total of six introns were present in the smaller U. pertusa mtDNA (Up2), while the larger mtDNA (Up1) had eight. The larger mtDNA had two additional group II introns in two genes (cox1 and cox2) and tandem duplication mutations in noncoding regions. Our results showed the first case of intraspecific variation in chlorophytan mitogenomes and provided further genomic data for the undersampled Ulvophyceae.

The species in family Planctomycetaceae are ideal groups for investigating the origin of eukaryotes. Their cells are divided by a lipidic intracytoplasmic membrane and they share a number of eukaryote-like molecular characteristics. However, their genomic structures, potential abilities, and evolutionary status are still unknown. In this study, we searched for common protein families and a core genome/pan genome based on 11 sequenced species in family Planctomycetaceae. Then, we constructed phylogenetic tree based on their 832 common protein families. We also annotated the 11 genomes using the Clusters of Orthologous Groups database. Moreover, we predicted and reconstructed their core/pan metabolic pathways using the KEGG (Kyoto Encyclopedia of Genes and Genomes) orthology system. Subsequently, we identified genomic islands (GIs) and structural variations (SVs) among the five complete genomes and we specifically investigated the integration of two Planctomycetaceae plasmids in all 11 genomes. The results indicate that Planctomycetaceae species share diverse genomic variations and unique genomic characteristics, as well as have huge potential for human applications.

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SUMMARY Ulva prolifera is a green‐tide‐forming macroalga dominating the green tides in the Yellow Sea from 2007 to 2019. The exponential growth of U. prolifera, and the correlating accumulation of biomass, rely heavily on its carbon fixation capability. Despite the importance of carbon fixation in algal growth, to date none of the genes involved in carbon fixation have undergone molecular characterization in U. prolifera. This study used Rapid Amplification of cDNA Ends (RACE) to characterize one full‐length carbonic anhydrase (CA) gene of U. prolifera (UpαCA1). An activity assay showed that UpαCA1 was an active CA. Real‐time quantitative PCR results showed that temperature, irradiance, salinity and pH could influence the transcriptional level of UpαCA1, indicating that UpαCA1 was sensitive to varying environmental factors. The results of this study provided further insights into our understanding of the influence of environmental factors on carbon fixation in U. prolifera and its subsequent role in the formation of green tides.

Coscinodiscus is a genus common in marine phytoplankton, with some species thought to have a significant negative ecological impact. However, the availability of their genome sequences is rather limited. Here, we assembled and annotated the first complete mitochondrial genome (mtDNA) of the species Coscinodiscus granii L.F.Gough 1905, as part of our efforts to gain a better understanding of the genetic characteristics of Coscinodiscus taxa at a genomic level. The circular mtDNA was 34,970 bp in length and encoded 60 genes, including 32 protein-coding genes (PCGs), 24 transfer RNA (tRNA) genes, two ribosomal RNA (rRNA) genes, and two conserved open reading frames (orfs). The overall GC content of C. granii mtDNA was 24.30%, which was slightly lower than that of C. wailesii (25.00%), the first species in the genus Coscinodiscus whose mtDNA has been reported, and higher than that of Melosira undulata (21.60%), the first species in the class Coscinodiscophyceae whose mtDNA has been reported. As expected for congeneric species, phylogenetic analysis using concatenated amino acid sequences of 27 shared PCGs suggested that C. granii has a closer evolutionary relationship with C. wailesii. Coscinodiscus was found to be monophyletic in the phylogeny. The complete mtDNAs of more Coscinodiscus species will facilitate the exploration of the evolutionary relationships of species in the Class Coscinodiscophyceae.

Ulva intestinalis Linnaeus 1753 (Ulvophyceae, Chlorophyta) is a marine green macroalga that is distributed on coasts of the Yellow Sea and the Bohai Sea in China. Here, the complete chloroplast genome of U. intestinalis was constructed and analyzed comparatively. The chloroplast genome of U. intestinalis is a 99,041-bp circular molecule that harbors a total of 112 genes including 71 protein-coding genes (PCGs), 26 transfer RNA genes (tRNAs), three ribosomal RNA genes (rRNAs), three free-standing open reading frames ( orf s) and nine intronic orf s, and ten introns in seven genes ( atpA , infA , psbB , psbC , petB , rrnL , and rrnS ). The maximum likelihood (ML) phylogenomic analysis shows that U. intestinalis firstly groups with Ulva compressa , and then these two species together with the Ulva australis – Ulva fenestrata – Ulva rotundata subclade form a monophyletic clade, Ulva lineage II. U. intestinalis chloroplast genome is the only one in Ulva lineage II where the reversal of a collinear block of two genes ( psbD – psbC ) did not occur, and its genome structure is consistent with that of most chloroplast genomes in Ulva lineage I, indicating that the similarity of genome structure is not completely related to the genetic relationship of Ulva species. Our genomic data will facilitate the development of specific high-resolution chloroplast molecular markers for rapid identification of U. intestinalis , and help us understand its population diversity and genetic characteristics on a global scale.