Analysis of prenyltransferase gene expression in Pseudo-nitzschia multiseries

Domoic acid is a potent neurotoxin produced by the genus Pseudo-nitzschia. It is responsible for causing amnesic shellfish poisoning, a condition capable of devastating marine wildlife and humans with severe neurological complications once ingested. Much of the biosynthetic pathway, its regulation, and the biological function of domoic acid remains to be elucidated. Recent research has found N-geranyl-L-glutamic acid as the true precursor to domoic acid. This is formed by the condensation of two metabolites, geranyl diphosphate and glutamate. The former, geranyl diphosphate, is synthesized through a condensation of isopentenyl diphosphate and dimethylallyl diphosphate. This initial step is catalyzed by a geranyl diphosphate synthase, a member of the prenyltransferase family. Here, expression of three prenyltransferase genes (Psemu2, Psemu3, and Psemu4) was analyzed through quantitative polymerase chain reaction in three strains of P. multiseries isolated from different growth phases to correlate relative abundance with domoic acid accumulation. Of the three transcripts, Psemu3 and Psemu4 were previously identified as potential geranyl diphosphate synthases in homology modeling studies. Psemu2 and Psemu3 consistently had higher relative expression over Psemu4 in all three strains. Prenyltransferase expression also decreased as domoic acid concentration reached an apparent maximum in late-log and stationary phase. This demonstrates that prenyltransferase transcripts Psemu2 and Psemu3 are highly expressed in log phase, and possibly may play a role in domoic acid biosynthesis.