Volvox africanus NIES-3780 asexual spheroid. Image credit: Hisayoshi Nozaki.

V. africanus NIES-3780 bisexual (monoicous) sexual spheroid with eggs and sperm packet (bundle of male gametes). Image credit: Hisayoshi Nozaki.

Parental spheroid containing male, bisexual and asexual spheroids of the next generation. Image credit: Hisayoshi Nozaki.

The Volvox africanus NIES-3780 genome sequence and gene models were not determined by the Joint Genome Institute (JGI), but were downloaded from NCBI on March 6, 2023. All published models are available as ExternalModels. In order to ensure this genome is comparable to those sequenced annotated by the JGI , we applied standard filters to ExternalModels to produce the initial GeneCatalog. A total of 11,013 of 23,635 external models were excluded based on one of the following classifications: 1) association with repetitive elements, 2) pseudogenes with internal stop codons, 3) alternative isoforms or overlapping transcript models, 4) alleles on secondary/smaller 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.

Volvox africanus NIES-3780

Volvox africanus is a multicellular chlorophyte alga found in freshwater habitats. Asexual spheroids are haploid and normally reproduce by production of daughter spheroids. When sexual reproduction is induced, V. africanus forms both male and female gametes (sperm and eggs, respectively) in sexual spheroids within a single clonal culture (homothallism) (Nozaki et al. 2015). V. africanus strain NIES-3780 forms both bisexual and unisexual male spheroids. Since V. africanus is very closely related to a heterothallic species, V. reticuliferus, comparison of the whole sequences of the two species provided exciting insights into the evolution of homothallism in haploid organisms (Yamamoto et al. 2021). Further comparative studies of these two species promises deeper insights into evolution and diversity of mating systems in eukaryotes.