Chemistry of oxylipin pathways in marine diatoms

Abstract

Oxylipins are important signal transduction molecules widely distributed in animals and plants where they regulate a variety of events associated with physiological and pathological processes. The family embraces several different metabolites that share a common origin from the oxygenase-catalyzed oxidation of polyunsaturated fatty acids. The biological role of these compounds has been especially studied in mammalians and higher plants, although a varied and very high concentration of these products has also been reported from marine macroalgae. This article gives a summary of our results concerning the oxylipin chemistry of marine diatoms, a major class of planktonic microalgae that discourage predation from their natural grazers, zooplanktonic copepods, using chemical warfare. These apparently harmless microscopic cells produce a plethora of oxylipins, including short-chain unsaturated aldehydes, hydroxyl-, keto-, and epoxyhydroxy fatty acid derivatives, that induce reproductive failure in copepods through abortions, congenital malformations, and reduced larval growth. The biochemical process involved in the production of these compounds shows a simple regulation based on decompartmentation and mixing of preexisting enzymes and requires hydrolysis of chloroplast-derived glycolipids to feed the downstream activities of C16 and C20 lipoxygenases.

Dose-dependent regulation of microbial activity on sinking particles by polyunsaturated aldehydes: Implications for the carbon cycle

“…Alternatively, multiple chain lengths of PUAs together are often more potent than the same chain lengths separately, as has been observed for the metabolic activity of coastal free-living bacteria (16). Diatoms often release multiple chain lengths of PUAs at once (45), and the accumulation of heptadienal, octadienal, and decadienal in many of our noamendment controls suggest that this is the case on sinking particles across the North Atlantic (Fig. 3).…”

Induced defences in marine and freshwater phytoplankton: a review

“…The production of PUAs can also be accompanied by the synthesis of other products (collectively termed oxylipins) derived from the lipoxygenase-mediated oxidation of membrane lipids (Fontana et al, 2007b).…”

Diatom-derived oxylipins induce cell death in sea urchin embryos activating caspase-8 and caspase 3/7

“…However, their beneficial role in supporting marine food chains has been challenged with the discovery that some diatom species produce secondary metabolites with cytotoxic activity (Miralto et al, 1999). These cytotoxic compounds are the end-products of a lipoxygenase/hydroperoxide lyase metabolic pathway (Fontana et al, 2007) initiated by damage to algal cells, including short chain polyunsaturated aldehydes (PUAs) and other oxygenated fatty acid degradation products such as hydroxides, oxo-acids and epoxyalcohols, collectively termed oxylipins. Oxylipins from marine diatoms are known to be disruptive to reproductive and developmental processes of several marine invertebrates (Caldwell, 2009).…”