Lipoxygenase pathways in marine diatoms: identification, occurrence and regulation of lipolytic acyl hydrolases (LAHs)

Diatoms are eukaryotic microalgae broadly present in freshwater and marine ecosystems. They are responsible for about 40% of the marine primary production and 20% of global primary production. The organic material formed through these processes is at the bases of the marine food chain and, in this way, supports the entire life on the planet. About the physiological and ecological studies on diatoms, however, only in recent years has begun to understand the molecular aspects. In analogy with higher plants and brown algae, diatoms possess lipoxygenase able to produce oxygenated compounds of poly-unsaturated fatty acids. In diatoms, these molecules, generically called oxylipins, show an unusual structural variability that seems to depend on genetic diversity. It is believed that the oxylipins have functions of intraspecific or interspecific chemical signal, however, these studies have always been limited by the lack of knowledge of the molecular mechanisms that regulate the biosynthesis of these compounds. Based on functional and tracer studies, it has been proposed that the process leading to the formation of oxylipins is due to a galactolipid hydrolyzing activity that, like lipolytic acyl hydrolases (LAHs) of land plants, is also capable of converting phospholipids. This doctoral study has focused the molecular identification of lipolytic acid hydrolases (LAHs), in three ecologically relevant diatoms: Pseudo-nitzschia multistriata, Pseudo-nitzschia arenysensis, and Skeletonema marinoi.