Dinoflagellata

Abstract

Dinoflagellates are a major group of aquatic protists responsible for a major part of marine primary productivity, the creation of coral reefs, marine bioluminescence, and most toxic red tides; indirectly they also cause some human diseases like paralytic shellfish poisoning, ciguatera, etc. They are derived from photosynthetic ancestors and early in their evolutionary history exchanged most of the histones in their nuclei for DVNPs, proteins of putatively viral origin that caused a complete reorganization of chromosomes that includes the loss of the typical eukaryotic nucleosomes and a very marked increase in total amounts of DNA per nucleus. Later on, they acquired other types of DNA-binding proteins, so-called HLPs in at least two waves, possibly lateral transfers from bacteria. Dinoflagellate mitochondrial genomes are some of the smallest known, and the genomes of the ancestral plastid type of the group, the peridinin plastids, are atomized into mini-circles with usually one single gene per circle. Roughly half of the dinoflagellates are non-photosynthetic, and the majority of the photosynthetic forms have peridinin plastids. Loss of photosynthesis has occurred repeatedly, but all free-living non-photosynthetic forms remain metabolically dependent on cryptic plastids; complete loss of plastid metabolic activity has only been shown in a few parasitic forms. Several lineages show a marked propensity for reacquisition of photosynthesis, be it in the form of permanent photosynthetic endosymbionts, kleptochloroplasts, or serial secondary and tertiary endosymbioses that produce cells with a wide variety of plastid types. In a few members of the group, peridinin plastids have become the pigment cup/retinoid of complex eyelike structures, so-called ocelli.