Volvox, the most sophisticated member of the lineage, is believed to have evolved from a Chlamydomonas-like ancestor within the last 200 million years, making the two living organisms an appealing model to study the evolutionary changes that brought about multicellularity and cellular differentiation.
To gather data for the comparative genomic analysis, the researchers sequenced the 138 million base pair Volvox genome using a whole genome shotgun strategy. The genome itself is 17% larger than the previously sequenced genome of Chlamydomonas and the sequence divergence between the two is comparable to that between human and chicken.
Despite the modest increase in genome size, the number of predicted proteins turned out to be very similar for the two organisms (14,566 in Volvox vs. 14,516 in Chlamydomonas) and no significant differences could be identified in the repertoires of protein domains or domain combinations. Protein domains are parts of proteins that can evolve, function, and exist independently of the rest of the protein chain.
"This was somewhat unexpected," explains Umen, "since innovation at the domain level was previously thought to play a role in the evolution of multicellularity in the plant and animal lineages."
In contrast to the overall lack of innovation, protein families specific to volvocine algae, such as extracellular matrix proteins, were enriched in Volvox compared to <
|Contact: Susan Trebach|