Both modular and single‐domain Type I polyketide synthases are expressed in the brevetoxin‐producing dinoflagellate, Karenia brevis (Dinophyceae)

Abstract

Dinoflagellates are prolific producers of polyketide compounds, many of which are potent toxins with adverse impacts on human and marine animal health. To identify polyketide synthase (PKS) genes in the brevetoxin‐producing dinoflagellate, Karenia brevis, we assembled a transcriptome from 595 million Illumina reads, sampled under different growth conditions. The assembly included 125,687 transcripts greater than 300 nt in length, with over half having >100× coverage. We found 121 transcripts encoding Type I ketosynthase (KS) domains, of which 99 encoded single KS domains, while 22 contained multiple KS domains arranged in 1–3 protein modules. Phylogenetic analysis placed all single domain and a majority of multidomain KSs within a monophyletic clade of protist PKSs. In contrast with the highly amplified single‐domain KSs, only eight single‐domain ketoreductase transcripts were found in the assembly, suggesting that they are more evolutionarily conserved. The multidomain PKSs were dominated by trans‐acyltransferase architectures, which were recently shown to be prevalent in other algal protists. Karenia brevis also expressed several hybrid nonribosomal peptide synthetase (NRPS)/PKS sequences, including a burA‐like sequence previously reported in a wide variety of dinoflagellates. This contrasts with a similarly deep transcriptome of Gambierdiscus polynesiensis, which lacked NRPS/PKS other than the burA‐like transcript, and may reflect the presence of amide‐containing polyketides in K. brevis and their absence from G. polynesiensis. In concert with other recent transcriptome analyses, this study provides evidence for both single domain and multidomain PKSs in the synthesis of polyketide compounds in dinoflagellates.

Transcriptomic investigation into polyketide toxin synthesis in Ostreopsis (Dinophyceae) species

“…Variations of the GYLG motif (DYLG, HYLG, YYLG, GLLG, AYLG and ALLG) were also observed in this study in the four transcriptomes and have been also been reported from previous dinoflagellate libraries (Monroe and Van Dolah, ; Eichholz et al ., ; Pawlowiez et al ., ; Meyer et al ., ; Van Dolah et al ., ) (Fig. ).…”

“…Our KS phylogenetic tree reports similar evolutionary trends compared to previous studies, such as the three iterative dinoflagellate sub‐clades amongst the ‘protistan’ clade and numerous multiple (modular) KS domains, with the addition of NRPS/PKS hybrid clades that are closely related to bacterial type I PKS clade (Monroe and Van Dolah, ; López‐Legentil et al ., ; Eichholz et al ., ;Kohli et al ., ; Van Dolah et al ., ). All single KS domain identified in this study from the four dinoflagellate species belonged to either one of the three protistian sub‐clades that have been previously described suggesting that these single domain transcripts are of dinoflagellate origin and not due to bacterial and fungal contaminations in the cultures.…”

“…Recently, Van Dolah et al . () identified six NRPS/PKS hybrids from K . brevis , which could be linked to the biosynthesis of talulamide, brevisamide and other known amide‐containing compounds from K .…”

Natural Voltage‐Gated Sodium Channel Ligands: Biosynthesis and Biology

“…Murray and co‐workers revealed the most comprehensive collection of polyketide synthase genes in dinoflagellates so far from the genomes of Gambierdiscus polynesiensis and Gambierdiscus excentricus , some of which could be associated with the production of ciguatoxins . Concurrently, Murray and co‐workers published a transcriptome from K. brevis which revealed several single and multidomain polyketide synthases potentially involved in the production of brevetoxins . This cutting edge work by Murray provides new clues toward understanding the enzymes involved in assembling the complex polyether ladder scaffolds.…”

“…[80] Concurrently, Murray andc o-workersp ublished at ranscriptome from K. brevis which revealed several single and multidomainp olyketide synthases potentially involved in the production of brevetoxins. [82] This cutting edge work by Murray provides new clues toward understanding the enzymes involvedi na ssembling the complex polyether ladder scaffolds.…”