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The rbcS multigene family evolved through complex duplication events leading to species-specific gene copies. Selection and coevolution with rbcL constrained rbcS evolution thereby limiting the divergence of each gene copy., Ribulose-1,5-bisphosphate carboxylase/oxygenase (RuBisCO) is considered to be the main enzyme determining the rate of photosynthesis. The small subunit of the protein, encoded by the rbcS gene, has been shown to influence the catalytic efficiency, CO2 specificity, assembly, activity, and stability of RuBisCO. However, the evolution of the rbcS gene remains poorly studied. We inferred the phylogenetic tree of the rbcS gene in angiosperms using the nucleotide sequences and found that it is composed of two lineages that may have existed before the divergence of land plants. Although almost all species sampled carry at least one copy of lineage 1, genes of lineage 2 were lost in most angiosperm species. We found the specific residues that have undergone positive selection during the evolution of the rbcS gene. We detected intensive coevolution between each rbcS gene copy and the rbcL gene encoding the large subunit of RuBisCO. We tested the role played by each rbcS gene copy on the stability of the RuBisCO protein through homology modelling. Our results showed that this evolutionary constraint could limit the level of divergence seen in the rbcS gene, which leads to the similarity among the rbcS gene copies of lineage 1 within species.

Polyploidization occurs widely in eukaryotes, and especially in plants. Polyploid plants and some fishes have been commercialized. Typically, severe genomic perturbations immediately follow polyploidization and little is known about how polyploid offspring survives the genetic and epigenetic changes. Investigations into this require the identification of genes related to polyploidization and the discrimination of dosage-balance from paternal and maternal copies, and regardless of the mechanism being either autopolyploidization or allopolyploidization. New approaches and technologies may discern the mosaic of novel gene functions gained through the recombination of paternal and maternal genes in allopolyploidization. Modifications of Clustered Regularly Interspaced Short Palindromic Repeats (CRISPR) with CRISPR-associated system (Cas) protein 9 (CRISPR/Cas9) have been employed in studies of polyploidization of plants. However, the approach has seldom been applied to polyploidization in vertebrates. Herein, we use CRISPR/Cas9 to trace gene-fate in tetraploid goldfish, and specifically to identify the functional differentiation of two divergent copies of fgf20a, which are expressed differently throughout embryonic development. We expect this gene editing system will be applicable to studies of polyploids and the genetic improvement of polyploid livestock.

Background Bdelloid rotifers are microscopic animals that have apparently survived without sex for millions of years and are able to survive desiccation at all life stages through a process called anhydrobiosis. Both of these characteristics are believed to have played a role in shaping several unusual features of bdelloid genomes discovered in recent years. Studies into the impact of asexuality and anhydrobiosis on bdelloid genomes have focused on understanding gene copy number. Here we investigate copy number and sequence divergence in alpha tubulin. Alpha tubulin is conserved and normally present in low copy numbers in animals, but multiplication of alpha tubulin copies has occurred in animals adapted to extreme environments, such as cold-adapted Antarctic fish. Using cloning and sequencing we compared alpha tubulin copy variation in four species of bdelloid rotifers and four species of monogonont rotifers, which are facultatively sexual and cannot survive desiccation as adults. Results were verified using transcriptome data from one bdelloid species, Adineta ricciae. Results In common with the typical pattern for animals, monogonont rotifers contain either one or two copies of alpha tubulin, but bdelloid species contain between 11 and 13 different copies, distributed across five classes. Approximately half of the copies form a highly conserved group that vary by only 1.1% amino acid pairwise divergence with each other and with the monogonont copies. The other copies have divergent amino acid sequences that evolved significantly faster between classes than within them, relative to synonymous changes, and vary in predicted biochemical properties. Copies of each class were expressed under the laboratory conditions used to construct the transcriptome. Conclusions Our findings are consistent with recent evidence that bdelloids are degenerate tetraploids and that functional divergence of ancestral copies of genes has occurred, but show how further duplication events in the ancestor of bdelloids led to proliferation in both conserved and functionally divergent copies of this gene.