Abstract:
Understanding how organisms deal with potentially toxic or fitness-reducing
allelochemicals is important for understanding patterns of predation and herbivory in the
marine environment. The ability of marine consumers to tolerate dietary toxins may
involve biochemical resistance mechanisms, which increase the hydrophilicity of
compounds and facilitate their active efflux out of sensitive cells and tissues. While
several allelochemical-responsive detoxification enzymes have been sequenced and
functionally characterized in terrestrial invertebrates feeding on chemically defended host
plants, there is virtually no information concerning the role of these biotransformation
enzymes that may mediate feeding tolerance in marine invertebrates. The objective of
this research was to assess the diversity and dietary regulation of cytochrome P450s
(CYP), glutathione S-transferases (GST) and ABC transporters in the generalist marine
gastropod Cyphoma gibbosum feeding on a variety of chemically defended gorgonian
corals, and to identify those dietary natural products that act as substrates for these
proteins.
Molecular and proteomic techniques identified both allelochemically-responsive
CYPs, and constitutively expressed GSTs and transporters in Cyphoma digestive glands.
Inhibition of Cyphoma GST activity by gorgonian extracts and selected allelochemicals
(i.e., prostaglandins) indicated that gorgonian diets are likely to contain substrates for
molluscan detoxification enzymes. In vitro metabolism studies with recombinant CYPs
suggested those Cyphoma enzymes most closely related to vertebrate fatty acid
hydroxylating enzymes may contribute to the detoxification of ichthyodeterrent
cyclopentenone prostaglandins found in abundance in selected gorgonian species.
Finally, the presence and activity of multixenobiotic resistance transporters in Cyphoma
and the co-occuring specialist nudibranch, Tritonia hamnerorum, suggests these efflux
transporters could function as a first line of defense against dietary intoxication.
Together, these results suggest marine consumers that regularly exploit allelochemical-rich
prey have evolved both general (GST and ABC transporters) and allelochemical-specific
(CYP) detoxification mechanisms to tolerate prey chemical defenses.
