Dinoflagellates, the major photosynthetic symbiont of corals and the key agents of harmful algal blooms (HABs), are an important group of microalgae in aquatic ecosystems. We found that major components of the DNA Damage Response (DDR) pathways, including photoreactivation, base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), non-homologous end joining repair (NHEJ) and homologous recombination repair (HR) were well represented in dinoflagellate genomes. Putative DDR components were also expressed under the normal dinoflagellate vegetative cycles, which could be related to the replication stresses associated with the tandem repeat arrays (TRAs), a common mode of gene encoding amongst these largest genomes.

Transcriptomic analysis of heterotrophic dinofla...[ Read more ]

Dinoflagellates, the major photosynthetic symbiont of corals and the key agents of harmful algal blooms (HABs), are an important group of microalgae in aquatic ecosystems. We found that major components of the DNA Damage Response (DDR) pathways, including photoreactivation, base excision repair (BER), nucleotide excision repair (NER), mismatch repair (MMR), non-homologous end joining repair (NHEJ) and homologous recombination repair (HR) were well represented in dinoflagellate genomes. Putative DDR components were also expressed under the normal dinoflagellate vegetative cycles, which could be related to the replication stresses associated with the tandem repeat arrays (TRAs), a common mode of gene encoding amongst these largest genomes.

Transcriptomic analysis of heterotrophic dinoflagellate Crypthecodinium cohnii, in response to Ultraviolet-C radiation (UVc), showed an overall downregulation of transcripts involved in replication and transcription, consistent with our observed UVc dosage-dependent cell cycle delay. Selective upregulation of component homologues in BER and NER, but not in other pathways were observed. Interestingly, transcripts of conventional UVr-responsive CPD photolyases, which was expressed in normal vegetative cycles without light activation, were not elevated in response to UVc.

In addition to its upregulation during sexual reproduction, we also reported expression of a meiotic recombinase ccDmc1p of the RecA/Rad51/Dmc1 superfamily in both vegetative cycles and in response to UVc. Taken together, the cumulative results of DDR components being expressed in normal vegetative cycles, and the lack of significant upregulation of most DDR pathway, indicated dinoflagellates likely incorporated canonical damage repair genes in the maintenance of TRAs which encode most of the dinoflagellate genes.

Our findings in UVc dosage responses will have immediate value in the deployment of UVc for the harmful algal blooms and of ballast water treatment. These first studies of dinoflagellate DDR pathways, including the response to UVc irradiation, will form the basis for future investigations in relation to both DDR and UVc response. Increasing UVc levels, with the advent of climate change associated ozone depletion, and the extension of traditional ozone depletion regions, will lead to increasing influence of UVc to future oceanic regimes.