Genetic Diversity, Morphological Uniformity and Polyketide Production in Dinoflagellates (Amphidinium, Dinoflagellata)

Tamsyn Garby,Mona Hoppenrath,Shauna A. Murray,Brett A. Neilan

doi:10.1371/journal.pone.0038253

Tamsyn Garby, Mona Hoppenrath + Show 2 more

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https://doi.org/10.1371/journal.pone.0038253

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Abstract

Dinoflagellates are an intriguing group of eukaryotes, showing many unusual morphological and genetic features. Some groups of dinoflagellates are morphologically highly uniform, despite indications of genetic diversity. The species Amphidinium carterae is abundant and cosmopolitan in marine environments, grows easily in culture, and has therefore been used as a ‘model’ dinoflagellate in research into dinoflagellate genetics, polyketide production and photosynthesis. We have investigated the diversity of ‘cryptic’ species of Amphidinium that are morphologically similar to A. carterae, including the very similar species Amphidinium massartii, based on light and electron microscopy, two nuclear gene regions (LSU rDNA and ITS rDNA) and one mitochondrial gene region (cytochrome b). We found that six genetically distinct cryptic species (clades) exist within the species A. massartii and four within A. carterae, and that these clades differ from one another in molecular sequences at levels comparable to other dinoflagellate species, genera or even families. Using primers based on an alignment of alveolate ketosynthase sequences, we isolated partial ketosynthase genes from several Amphidinium species. We compared these genes to known dinoflagellate ketosynthase genes and investigated the evolution and diversity of the strains of Amphidinium that produce them.

Highlights

Dinoflagellates are a unique group of microbial eukaryotes that play a variety of important ecological roles, notably as the core of aquatic food webs, in symbioses with invertebrates such as corals, and as the agents responsible for producing harmful algal bloom toxins (HABs)
Given the high level of genetic diversity found in studies of species of Amphidinium, the aim of this study was to examine novel strains of the ‘lab rat’ dinoflagellate Amphidinium carteae and the closely related species Amphidinium massartii using nuclear (ITS, LSU ribosomal RNA (rRNA)) and mitochondrial gene markers, and light and scanning electron microscopy, in order to determine whether cryptic species may be present
As we found intraspecific divergence levels in ITS rDNA within clades of A. carterae and A. massartii of 4–10 times this level, this would suggest that the clades of A. carterae and A. massartii represent cryptic species of Amphidinium

Summary

Introduction

Dinoflagellates are a unique group of microbial eukaryotes that play a variety of important ecological roles, notably as the core of aquatic food webs, in symbioses with invertebrates such as corals, and as the agents responsible for producing harmful algal bloom toxins (HABs) While eukaryotic, they possess many characteristics not seen in typical eukaryotes, such as a fifth base replacing uracil in their DNA [1,2], unusually large genomes, greatly reduced chloroplast genomes [3], permanently condensed chromosomes lacking in histones [2], and complex organelle structures such as eyespots [4]. A. carterae has been used as a ‘model dinoflagellate’ in breakthrough studies of the dinoflagellate plastid including the peridinin-chloroplast A-protein light-harvesting antenna complex [9,10,11,12], the unique dinoflagellate genome [13], the first successful genetic transformation of a dinoflagellate [14] and the first polyketide synthase gene cluster from a dinoflagellate [15]

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