iTRAQ-Based Quantitative Proteomic Analysis of a Toxigenic Dinoflagellate Alexandrium catenella and Its Non-toxigenic Mutant Exposed to a Cell Cycle Inhibitor Colchicine

Abstract

Paralytic shellfish toxins (PSTs) are a group of potent neurotoxic alkaloids mainly produced by marine dinoflagellates and their biosynthesis is associated with the cell cycle. Study shows that colchicine can cease cell division and inhibit PST production of dinoflagellates. However, the molecular mechanism behind this linkage is unknown. Here, we applied the iTRAQ-based proteomic approach to investigate protein expression profiles of a toxigenic dinoflagellate Alexandrium catenella (ACHK-T) and its non-toxigenic mutant (ACHK-NT) when treated with colchicine. The results showed that the cell cycles of both strains were arrested at the G1 phase by colchicine, and the toxin biosynthesis of ACHK-T was inhibited. Among 6,988 proteins identified, 113 and 253 proteins were differentially expressed in the colchicine-treated ACHK-T and ACHK-NT, respectively, compared with their non-colchicine treatments. Proteins involved in reactive oxygen species scavenging and protein degradation were upregulated in both strains while proteins participating in photosynthetic pigment biosynthesis and nitrogen metabolism presented different expressions. Nitrate reductase and glutamine synthetase were altered insignificantly in the colchicine-treated ACHK-T while both of them were remarkably downregulated in the colchicine-treated ACHK-NT, suggesting a feedback regulation between PST production and nitrogen metabolism in ACHK-T. Nitrogen originally for PST biosynthesis might be reallocated to photosynthetic pigment biosynthesis in the colchicine-treated ACHK-T. A total of 55 homologs of 7 toxin-related proteins were obtained; however, they altered insignificantly in both colchicine-treated strains, suggesting that toxin biosynthesis might be post-translationally regulated. Our study provided new insights into toxin biosynthesis in marine dinoflagellates.

Biosynthesis of Saxitoxin in Marine Dinoflagellates: An Omics Perspective

“…These studies outlined that the elevated photosynthesis rate in the non-toxic mutant of A. catenella might contribute to its higher growth rate compared to its toxic counterpart. In another investigation, the proteomics analysis of mutated saxitoxin-producing A. catenella exposed to a cell-cycle inhibitor colchicine revealed the upregulation of several proteins involved in photosynthesis and carotenoid biosynthesis during the arrested toxin production stage, indicating the channeling of nitrogen compounds originally allocated for saxitoxin biosynthesis toward the synthesis of carotenoid and nitrogenous chlorophyll [96]. However, these claims can be contended with a finding by Jiang et al [97] of several photosynthesis-related proteins having enhanced expression during the highly toxic period of saxitoxin-producing A. tamarense, which can be reflected back to a study by Etheridge and Roesler [98] that was unable to find a significant correlation between photosynthesis rate and toxin production in the toxic A. fundyense.…”

Production of Paralytic Shellfish Toxins (PSTs) in Toxic Alexandrium catenella is Intertwined with Photosynthesis and Energy Production

“…On the basis of these facts and in order to understand the mechanism of PST production, researchers compared the differences in genetic makeup and gene expression levels [ 14 , 15 , 16 ], as well as physiological properties among toxic and non-toxic algal strains in determining the differences in abilities to produce toxins. For example, the production of PSTs under the G1 phase was suggested in PST-producing A. fundyense [ 17 ] and was further validated by the G1 phase inhibitor experiment in another PST-producing species A. tamarense [ 18 , 19 ]. Nevertheless, only limited information on the PST production mechanism was gathered.…”

“…Hence, investigating differential protein expressions is reasonably one of the first steps to explore the mechanism of toxin synthesis. Such an approach with quantitative proteomics was reported in 2012 [ 22 ] and was refreshed by the same group in 2015 [ 23 ] and 2018 [ 19 ]. By comparing protein expression profiles of PST-producing A. catenella (AC) and its toxicity-lost mutant in both 2-dimensional gel electrophoresis [ 22 ] and iTRAQ-based shotgun proteomic basis [ 19 , 23 ], they reported the up-regulation of light-harvesting related proteins and methionine biosynthesis in the toxic strain.…”

“…Such an approach with quantitative proteomics was reported in 2012 [ 22 ] and was refreshed by the same group in 2015 [ 23 ] and 2018 [ 19 ]. By comparing protein expression profiles of PST-producing A. catenella (AC) and its toxicity-lost mutant in both 2-dimensional gel electrophoresis [ 22 ] and iTRAQ-based shotgun proteomic basis [ 19 , 23 ], they reported the up-regulation of light-harvesting related proteins and methionine biosynthesis in the toxic strain. Further, seven sxt gene-related suspects were identified but none of them were differentially expressed in-between the toxic and non-toxic counterparts [ 19 , 23 ].…”

In silicoprediction of the secretome from the invasive neurotoxic marine dinoflagellateAlexandrium catenella

“…When ingested by humans upon consumption of contaminated seafood, these toxins cause neural system perturbation that can lead to death (Hallegraeff, 1993;Quod and Turquet, 1996;Cusick and Sayler, 2013). The proteins involved in A. catenella toxin biosynthesis have been investigated in several studies (Wang et al, 2013;Zhang et al, 2015;Zhang et al, 2017;Zhang et al, 2018).…”