Photo of Pleodorina starrii NIES-4481 (female) female colonies from Dr. Kohei Takahashi.

Photo of Pleodorina starrii NIES-4481 (female) asexual colonies from Dr. Kohei Takahashi.

The Pleodorina starrii NIES-4481 genome sequence and gene models were not determined by the Joint Genome Institute (JGI), but were downloaded from NCBI on April 24, 2024. All published models are available as ExternalModels. In order to ensure this genome is comparable to those sequenced and annotated by the JGI, we applied standard filters to ExternalModels to produce the initial GeneCatalog. A total of 1285 external models were excluded based on one of the following classifications: 1) repetitive elements, 2) pseudogenes with internal stop codons, 3) alternative isoforms or overlapping transcript models, 4) alleles on secondary scaffolds, and 5) short models lacking functional annotation. Please note that this copy of the genome is not maintained by NCBI and is therefore not automatically updated. In order to allow comparative analyses with other algal genomes sequenced by the JGI, a copy of this genome is incorporated into PhycoCosm. The JGI Annotation Pipeline was used to add functional annotation to the genes.

Pleodorina starrii is a freshwater colonial green algae and was firstly established in 2006 originating from Lake Sagami, Japan (Nozaki et al. 2006a). In P. starrii, a male-specific gene OTOKOGI, the homolog of the minus-dominance gene MID of Chlamydomonas reinhardtii, has been reported for the first time among anisogamous/oogamous volvocine algae (Nozaki et al. 2006b). P. starrii has differentiated somatic and gametic cells. Asexual colonies are haploid and produce clonal daughter colonies. In sexual reproduction, gametic cells differentiate into sperm packets in male colonies and female gametes in female colonies. P. starrii has three distinct sex phenotypes; male that produces only male colonies, female that produces only female colonies, and bisexual that produces both male and female colonies within a clone (Takahashi et al. 2021). A comparative genomic study among the three sex phenotypes (NIES-1363 male, NIES-4481 female, NIES- 4479 bisexual) provided insights into the molecular genetic bases of the trioecy under a haploid sex-determining system (Takahashi et al. 2023). Further genomic studies will reveal detailed mechanisms and the origin of trioecy in this lineage. 

References

1. Nozaki, H., Ott, F. D., Coleman, A. W. Morphology, molecular phylogeny and taxonomy of two new species of Pleodorina (Volvoceae, Chlorophyceae). J. Phycol. 42, 1072–1080 (2006a). https://doi.org/10.1111/j.1529-8817.2006.00255.x 
2. Nozaki, H., Mori, T., Misumi, O., Matsunaga, S., Kuroiwa, T. Males evolved from the dominant isogametic mating type. Curr. Biol. 16, 1018–1020 (2006b). https://doi.org/10.1016/j.cub.2006.11.019 
3. Takahashi, K., Kawai-Toyooka, H., Ootsuki, R., Hamaji, T., Tsuchikane, Y., Sekimoto, H., Higashiyama, T., Nozaki, H. Three sex phenotypes in a haploid algal species give insights into the evolutionary transition to a self-compatible mating system. Evolution 75, 2984–2993 (2021). https://doi.org/10.1111/evo.14306