Galactolipids of the genus Amphidinium (Dinophyceae): an hypothesis that they are basal to those of other peridinin-containing dinoflagellates.

The genus Amphidinium is shown in many phylogenies to be basal to other peridinin-containing, photosynthetic dinoflagellates as one of the first photosynthetic genera to arise after the evolution of heterotrophic genera. As part of our continuing examination of the plastid-associated galactolipids, namely mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively), in dinoflagellates, we here examine the galactolipid composition of members of the genus Amphidinium. We show that this genus is characterized by an abundance of 20:5(n-3)/18:5(n-3) and 20:5(n-3)/18:4(n-3) forms of MGDG and DGDG (with sn-1/sn-2 regiochemical specificity of fatty acids), but also sometimes with generally lesser amounts of some polyunsaturated C₁₈/C₁₈ forms, thus placing the examined species within a previously identified cluster of C₂₀/C₁₈ MGDG- and DGDG-containing, peridinin-containing dinoflagellates. We also show that Testudodinium testudo, previously known as Amphidinium testudo, conversely falls within a previously identified C₁₈/C₁₈ cluster, indicating a distinct difference in galactolipid biosynthesis capability. While it is likely that further revision of the genus may occur in the future and/or more basal peridinin-containing, photosynthetic genera may be discovered, at the current time Amphidinium is the currently agreed-upon most basal dinoflagellate genus for which isolates are available for biochemical characterization such as what we describe in this paper. Thus, because of the presumed basal position of the genus Amphidinium, we present a hypothesis that its galactolipids currently represent those that are ancestral to other genera of peridinin-containing dinoflagellates, including those within the C₁₈/C₁₈ cluster. Amphidinium species' galactolipids reside within the C₂₀/C₁₈ peridinin dinoflagellate cluster. Conversely, Testudodinium testudo (formerly Amphidinium testudo) falls within the C₁₈/C₁₈ cluster. We hypothesize Amphidinium's galactolipids as basal to other peridinin dinoflagellates. [ABSTRACT FROM AUTHOR]