Bioinformatic and gene expression analysis of an SLC6 homolog in the toxin-producing marine diatom pseudo-nitzschia multiseries

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Henningsen, Brooks M.
Pseudo-nitzschia multiseries (Ps-n) is a marine pennate diatom that produces the neurotoxin, domoic acid (DA). The molecular processes involved in toxin synthesis have yet to be elucidated. Previous work generated a suite of candidate genes that were found to be up-regulated under toxin-producing conditions. One such gene showed high sequence homology to the SLC6 family of amino acid transporters, which have been found to transport an array of amino acid substrates. This thesis focused on further characterizing the gene structure and expression patterns of this gene which we have designated PSN0072. Sequence analysis of the predicted protein revealed a conserved domain found in the SLC6 transporter family. Alignment of this amino acid sequence with a functional alignment of SLC6 homologs revealed the conservation of functionally relevant residues, strengthening the putative identification of PSN0072 as a member of the SLC6 family. Gene expression analyses revealed a link between the regulation of this gene and DA levels. Interestingly, PSN0072 was also up-regulated under nitrogen limited conditions, a finding consistent with other characterized amino acid importers. The results presented in this thesis suggest that PSN0072 may be involved in the export of DA or the import of another amino acid substrate, either as a nitrogen source or as a precursor to DA synthesis. A possible hypothesis to explain the results presented is that PSN0072 may be able to perform both of these important functions to Ps-n physiology.