Win some, lose some: genome evolution in red algae.

Abstract

What's special about red algae? You might say that they have distinct pigments, the phycobiliproteins; unusual plastids with unstacked thylakoids; a different storage saccharide, floridean starch; or that some species have a unique triphasic life history and a special connection between cells, pit plugs. To me, what is most fascinating is what they don't have. There are no flagella and no centrioles. What is the result of not having flagella? One may think that this means at no stage in the life cycle can the organism swim. Red algae are, thus, aquatic organisms that sexually reproduce, but with extremely limited possibilities with respect to chemotaxic responses toward gametes of the other sex, complicating the fusion of gametes. For example, in red algae the male gametes are released and, by random movement of waves and currents, find a female gamete on a female plant; remember that the ocean is large with small areas where seaweeds are found and there are many red algal species, further complicating reproductive success. A lack of motility also means that unicellular planktonic red algae have a decreased capability to position themselves in the light environment. It is generally believed that the ancestral eukaryote had a flagellum (Koumandou et al. 2013), and therefore it must have been lost in red algae. Therefore, the flagella along with the capacity for directed movement, except limited (<1 mm) amoebic movement (Pickett-Heaps et al. 2001), have disappeared. This is likely to be a large handicap for red algae, suggesting that the evolutionary force that triggered the loss of flagella was very strong. So what happened, when and why? The answers to these questions have for a long time been a mystery, but recent increased knowledge on genes and genomes of red algae is starting to shed some light on this subject and on the general evolution of red algal genes and genomes. The article by Qiu et al. (2015) in this issue provides new, important insights into the evolution of red algal genomes, including the loss of genes, the loss of function, and the subsequent gain of genes through horizontal gene transfer. [...]