One of the main reasons that I study the biological diversity of dinoflagellates is that they are a living laboratory for the evolution of endosymbiotic organelles. This is at least in part because, although they have plastids (chloroplasts) that seem to be ancestral to the group, dinoflagellates are all purely photosynthetic organisms. Some are parasitic or predatory (and not photosynthetic at all), while others are predatory or “mixotrophic” (meaning they are capable of both photosynthesis and predation). Consider the video below, which shows Esoptrodinium isolated from a puddle on the University of Maryland Campus, enthusiastically eating a Chlamydomonas (video by Liam MacTurk):

Matt Parrow has done some very interesting work on plastid loss in Esoptrodinium. It is a fascinating story of plastid gain and loss in what seems to be a single species.

Although mixotrophy is not unique to dinoflagellates, it seems to have set them up for a complex history of gain and loss of photosynthesis. In some cases plastids have become specialized for functions very different from photosynthesis, while in other cases they seem to have been lost outright. In other cases the dinoflagellate is photosynthetic, but relies on a relatively newly acquired plastid that seems to have replaced the “native” plastid (which is pigmented with, and named for, an unusual carotenoid, peridinin). These replacement plastids are acquired by ingesting another alga and permanently retaining its plastid.

The acquisition of an organelle can also mean exchange genetic material with the host cell. Remember that the original plastid underwent extensive gene loss and exchange with the nuclear genome. Because plastids play several important roles in the cell, we decided to use our dinoflagellate transcriptomic dataset to explore the isoprenoid pathways in dinoflagellates. Isoprenoids are interesting because there are two distinct pathways that perform this essential biosynthesis in different organisms, the Mevalonate (MVP) and Non-Mevalonate (MEP or DOXP) pathways, with plants making use of both pathways. Our data suggest that dinoflagellates only use the DOXP pathway, but, interestingly, in species with secondary plastids derived from other algae, some of the genes in the pathway seem to have been replaced with genes from the plastid donor species. This is interesting, because it implies transfer of genes from nuclear genome to nuclear genome in the course of transfer of the organelle, and is one more indication that the transfer of organelles is a much more complex than simply moving a functional module into a new cell.

Bentlage, B., Rogers, T.S., Bachvaroff, T.R., and Delwiche, C.F. 2015. Complex ancestries of isoprenoid synthesis in dinoflagellates. J. Euk. Microbiol.