iTRAQ-Based Quantitative Proteomic Analysis of a Toxigenic Dinoflagellate Alexandrium catenella at Different Stages of Toxin Biosynthesis during the Cell Cycle

Abstract

Paralytic shellfish toxins (PSTs) are a group of potent neurotoxic alkaloids that are produced mainly by marine dinoflagellates. PST biosynthesis in dinoflagellates is a discontinuous process that is coupled to the cell cycle. However, little is known about the molecular mechanism underlying this association. Here, we compared global protein expression profiles of a toxigenic dinoflagellate, Alexandrium catenella, collected at four different stages of toxin biosynthesis during the cell cycle, using an isobaric tags for relative and absolute quantification (iTRAQ)-based quantitative proteomic approach. The results showed that toxin biosynthesis occurred mainly in the G1 phase, especially the late G1 phase. In total, 7232 proteins were confidently identified, and 210 proteins exhibited differential expression among the four stages. Proteins involved in protein translation and photosynthetic pigment biosynthesis were significantly upregulated during toxin biosynthesis, indicating close associations among the three processes. Nine toxin-related proteins were detected, and two core toxin biosynthesis proteins, namely, sxtA and sxtI, were identified for the first time in dinoflagellates. Among these proteins, sxtI and ompR were significantly downregulated when toxin biosynthesis stopped, indicating that they played important roles in the regulation of PST biosynthesis. Our study provides new insights into toxin biosynthesis in marine dinoflagellates: nitrogen balance among different biological processes regulates toxin biosynthesis, and that glutamate might play a key modulatory role.

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

“…Moreover, seven other potential sxt gene product homologs identified by proteomic approaches in that study did not show any expressional difference between the toxic and non-toxic mutant [ 23 ]. In another study documenting proteomic changes of A. catenella at different stages of PST biosynthesis where sxtA homolog was identified for the first time, expression of sxtA also remained stable throughout the cell cycle regardless of fluctuation of cellular toxin contents throughout the cell cycle [ 34 ]. Owing to the wide range of biochemical roles of SAM as well as insufficient information acquired, the relationship between MAT and toxin synthesis needs to be investigated thoroughly.…”

Genetic association of toxin production in the dinoflagellate Alexandrium minutum

“…The sxtG homologues were reported in PST-producing dinoflagellate species only [56] and sxtG expression was upregulated in experimental conditions favouring toxin production [96]. Similarly, sxtI expression was upregulated in conditions favouring toxin production, and downregulated when toxin synthesis was stopped [96, 97]. Although identifying the molecular bases of the production of the various analogues is beyond the scope of the present study, the case of the strain e (T1xNT1 cross) might be worth being mentioned.…”

The Genetic Basis of Toxin Biosynthesis in Dinoflagellates

“…Several proteomics studies have been performed to provide insight on the mechanisms and possible translational regulation of STX biosynthesis. Correlation between the PST biosynthesis pathway and other carbon and energy utilizing pathways has been observed [210,211]. Proteins involved in the translational machinery, photosynthetic pigment production, and toxin biosynthesis with linkages to arginine, which is an important PST precursor molecule, and glutamate biosynthesis, were found to be upregulated during the same stage of the cell cycle [211,212,213].…”

“…Correlation between the PST biosynthesis pathway and other carbon and energy utilizing pathways has been observed [210,211]. Proteins involved in the translational machinery, photosynthetic pigment production, and toxin biosynthesis with linkages to arginine, which is an important PST precursor molecule, and glutamate biosynthesis, were found to be upregulated during the same stage of the cell cycle [211,212,213]. Proteins involved in bioluminescence have been observed to be upregulated during toxin production [211] and found to be downregulated in a non-toxic strain with toxin related proteins [210].…”

“…Proteins involved in the translational machinery, photosynthetic pigment production, and toxin biosynthesis with linkages to arginine, which is an important PST precursor molecule, and glutamate biosynthesis, were found to be upregulated during the same stage of the cell cycle [211,212,213]. Proteins involved in bioluminescence have been observed to be upregulated during toxin production [211] and found to be downregulated in a non-toxic strain with toxin related proteins [210]. Hence, it can be concluded that the toxin biosynthesis might not be regulated as a single pathway rather than being regulated in concert with other biosynthetic pathways.…”