A new article in Plant Systematics and Evolution reports on an ‘unconventional’ actin gene in the Volvocales. Called ‘novel actin-like protein’ (NAP), the gene is present, along with a traditional actin gene, in Chlamydomonas reinhardtii, C. moewusii, and Volvox carteri. A team of researches from Chuo University and the University of Tokyo, led by Takako Kato-Minoura, sequenced NAP from several other volvocine species in an effort to understand its origin and function.
NAP can replace conventional actin for some functions, but it fails to do so for others, presumably because it has a lower ability to polymerize. This is consistent with the ‘duplication and subfunctionalization‘ model of gene origins (cdesign proponentsists love to pretend that evolutionary theory has no explanation for gene origins). By examining whole genome sequences of other Chlorophyte algae and plants, Dr. Kato-Minoura’s team found that NAP appears to be restricted to the Volvocales. An inferred gene tree of NAP sequences doesn’t contradict the (more or less) consensus view of volvocine phylogeny, but because of low support values, it’s hard to conclude much from this. Because NAP is present in both C. reinhardtii and C. moewusii, the authors conclude that it must have been present in their common ancestor, which would suggest that its origin precedes by a good bit the origin of multicellularity in the volvocine algae.