The genome of the freshwater monogonont rotifer Brachionus calyciflorus

Monogononta is the most speciose class of rotifers, with more than 2,000 species. The monogonont genus Brachionus is widely distributed at a global scale, and a few of its species are commonly used as ecological and evolutionary models to address questions related to aquatic ecology, cryptic speciation, evolutionary ecology, the evolution of sex and ecotoxicology. With the importance of Brachionus species in many areas of research, it is remarkable that the genome has not been characterized. This study aims to address this lacuna by presenting, for the first time, the whole‐genome assembly of the freshwater species Brachionus calyciflorus. The total length of the assembled genome was 129.6 Mb, with 1,041 scaffolds. The N50 value was 786.6 kb, and the GC content was 24%. A total of 16,114 genes were annotated with repeat sequences, accounting for 21% of the assembled genome. This assembled genome may form a basis for future studies addressing key questions on the evolution of monogonont rotifers. It will also provide the necessary molecular resources to mechanistically investigate ecophysiological and ecotoxicological responses. </p

Complete mitochondrial genome of the Antarctic copepod Tigriopus kingsejongenesis (Harpacticoida, Harpacticidae)

The complete mitochondrial genome was sequenced from the Antarctic harpacticoid copepod Tigriopus kingsejongensis. The sequenced genome size was 14,940 bp, possessing different gene order and contents to those of the congeneric species T. japonicus and T. californicus in the genus Tigriopus. The mitochondrial genome of T. kingsejongensis has 13 protein-coding genes (PCGs), 2 rRNAs, and 22 tRNAs. Of the 13 PCGs, CO1, ND3, ATP6, and CO3 genes had incomplete stop codons T–, T–, TA–, and T–, respectively. Furthermore, the stop codons of the remaining 11 PCGs were TAA or TAG, while the start codon of 13 PCGs was ATG (CO1, ND4, Cytb, ND2, ND1, CO2, ND6, ATP6, CO3 genes), ATT (ND5, ATP8 genes), and ATA (ND3, ND4L genes), respectively. The nucleotide of 13 PCGs of T. kingsejongensis mitogenome showed 53.42, 52.17, and 49.10% similarities to the copepods T. japonicus, T. californicus, and Amphiascoides atopus, respectively, while the amino acid similarities were 64.38, 63.86, and 62.40%, respectively

Microplastic Size-Dependent Toxicity, Oxidative Stress Induction, and p‑JNK and p‑p38 Activation in the Monogonont Rotifer (<i>Brachionus koreanus</i>)

In this study, we evaluated accumulation and adverse effects of ingestion of microplastics in the monogonont rotifer (<i>Brachionus koreanus</i>). The dependence of microplastic toxicity on particle size was investigated by measuring several <i>in vivo</i> end points and studying the ingestion and egestion using 0.05-, 0.5-, and 6-μm nonfunctionalized polystyrene microbeads. To identify the defense mechanisms activated in response to microplastic exposure, the activities of several antioxidant-related enzymes and the phosphorylation status of mitogen-activated protein kinases (MAPKs) were determined. Exposure to polystyrene microbeads of all sizes led to significant size-dependent effects, including reduced growth rate, reduced fecundity, decreased lifespan and longer reproduction time. Rotifers exposed to 6-μm fluorescently labeled microbeads exhibited almost no fluorescence after 24 h, while rotifers exposed to 0.05- and 0.5-μm fluorescently labeled microbeads displayed fluorescence until 48 h, suggesting that 6-μm microbeads are more effectively egested from <i>B. koreanus</i> than 0.05- or 0.5-μm microbeads. This observation provides a potential explanation for our findings that microbead toxicity was size-dependent and smaller microbeads were more toxic. <i>In vitro</i> tests revealed that antioxidant-related enzymes and MAPK signaling pathways were significantly activated in response to microplastic exposure in a size-dependent manner

AtCML8, a calmodulin-like protein, differentially activating CaM-dependent enzymes in Arabidopsis thaliana

Plants express many calmodulins (CaMs) and calmodulin-like (CML) proteins that sense and transduce different Ca(2+) signals. Previously, we reported divergent soybean (Glycine max) CaM isoforms (GmCaM4/5) with differential abilities to activate CaM-dependent enzymes. To elucidate biological functions of divergent CaM proteins, we isolated a cDNA encoding a CML protein, AtCML8, from Arabidopsis. AtCML8 shows highest identity with GmCaM4 at the protein sequence level. Expression of AtCML8 was high in roots, leaves, and flowers but low in stems. In addition, the expression of AtCML8 was induced by exposure to salicylic acid or NaCl. AtCML8 showed typical characteristics of CaM such as Ca(2+)-dependent electrophoretic mobility shift and Ca(2+) binding ability. In immunoblot analyses, AtCML8 was recognized only by antiserum against GmCaM4 but not by GmCaM1 antibodies. Interestingly, AtCML8 was able to activate phosphodiesterase (PDE) but did not activate NAD kinase. These results suggest that AtCML8 acts as a CML protein in Arabidopsis with characteristics similar to soybean divergent GmCaM4 at the biochemical levels.close7