Red Algal Genomics: A Synopsis

Abstract

The red algae (or Rhodophyta) are an ancient and diversified group of photoautotrophic organisms. A 1,200-million-year-old fossil has been assigned to Bangiomorpha pubescens, a Bangia-like fossil suggesting sexual differentiation (Butterfield, 2000). Most rhodophytes inhabit marine environments (98%), but many well-known taxa are from freshwater habitats and acidic hot springs. Red algae have also been reported from tropical rainforests as members of the subaerial community (Gurgel and Lopez-Bautista, 2007). Their sizes range from unicellular microscopic forms to macroalgal species that are several feet in length. In aquatic environments, they are found as members of the planktonic and benthonic communities. Rhodophytan life cycles are highly contrasting. They include simple life cycles characterized by binary cell division and complex triphasic, haplo-diplobiontic life cycles, with one haploid (gametophytic) and two diploid (tetrasporophytic and carposporophytic) generations. The latter life cycle can be either isomorphic or heteromorphic. This is dependent on whether or not gametophytes and tetrasporophytes are morphologically similar or dissimilar, respectively. Rhodophyta share many biochemical and ultrastructural features with other algal groups. However, they are often characterized by a unique set of features such as the absolute lack of flagella and centrioles, presence of phycobilisomes and unstacked thylakoids in the chloroplast, absence of parenchyma, and presence of pit-connections between cells. Rhodophyta are characteristically red in color, but other shades of green, brown, and purple are common. Photosynthetic pigments include chlorophyll a, which is accompanied by accessory pigments or phycobiliproteins. These phycobiliproteins are responsible for the alga’s red coloration. They include water-soluble pigments such as phycoerythrin (red), phycocyanin (blue), and allophycocyanin (blue-greenish) (Grossman et al., 1993). These red and blue pigments are associated into phycobilisomes, a light-harvesting complex, on the surface of thylakoids. In this report, a summary is presented of genomic studies targeting this algal group, the Rhodophyta, with suggestions for future research in phylogenomics.