Chemoecological studies on marine natural products: terpene chemistry from marine mollusks

Some species of nudibranchs (Mollusca) protect themselves from predatory attacks by storing defensive terpene chemicals acquired from dietary sponges (Porifera) in specialized body parts called MDFs (mantle dermal formations), often advertising their unpalatability to potential predators by means of bright coloration patterns. Consequently, the survival of these trophic specialist species is closely related to the possibility of obtaining the defensive tools from sponges that live in their immediate vicinity; therefore, it is important to determine as precisely as possible the chemical composition of nudibranch extracts prior to any ecological studies addressing issues that involve their alimentary behavior and their defensive strategies, including the significance of their color patterns. Some of our recent studies on the chemical composition of terpene extracts from nudibranchs belonging to the genera Chromodoris and Hypselodoris are summarized. We also report the development of a method to assay extracts and purified metabolites for their feeding deterrent activity against co-occurring generalist predators. In a recent chemoecological study, showing that repugnant terpene chemicals are accumulated at extremely high concentrations in exposed parts of the nudibranchs' bodies, the feeding deterrence assays were carried out on the generalist marine shrimp Palaemon elegans, very common in the Mediterranean. We have modified this assay for use with the Australian shrimp species P. serenus, and confirmed the ecological validity of the assay by analysis of extracts from species of sponges and mollusks that live in the same habitat as P. serenus. The deterrent properties of haliclonacyclamine alkaloids isolated from the sponge Haliclona sp. were demonstrated, with the alkaloid mixture demonstrating palatability deterrence at concentrations as low as 0.05 mg/mL, and complete deterrence at 0.75 mg/mL. In contrast, the diterpene thuridillin metabolites from the sacoglossan mollusk Thuridilla splendens did not deter feeding by P. serenus

Towards the genetic architecture of seed lipid biosynthesis and accumulation in Arabidopsis thaliana

We report the quantitative genetic analysis of seed oil quality and quantity in six Arabidopsis thaliana recombinant inbred populations, in which the parent accessions were from diverse geographical origins, and were selected on the basis of variation for seed oil content and lipid composition. Although most of the biochemical steps involved in lipid biosynthesis are known and the key genes have been identified, the regulation of the processes that results in the final oil composition and total amount is not understood. By using physically anchored markers it was possible to compare results across populations. A total of 219 quantitative trait loci (QTLs) were identified, of which 81 were significant at P<0.001. Some of these colocalise with QTLs identified previously, but many novel QTLs were also identified. The results highlight the importance of studying traits in multiple populations, which will lead to a better understanding of the contribution that natural variation makes to the genetic architecture of a phenotype

10-hydroxydarlingine, a new tropane alkaloid from the Australian proteaceous plant Triunia erythrocarpa

Triunia erythrocarpa was identified as containing alkaloids during chemical screening of Queensland Proteaceae using Dragendorff's reagent. A new tropane, 10-hydroxydarlingine (1), and the known tropane, darlingine (2), were isolated from the leaves of T. erythrocarpa. The absolute stereochemistry of 10-hydroxydarlingine (1) was assigned using the advanced Mosher method. T. erythrocarpa is only the seventh member of the Proteaceae to have been shown to produce alkaloids