Patatin-like lipolytic acyl hydrolases and galactolipid metabolism in marine diatoms of the genus Pseudo-nitzschia

Diatoms are eukaryotic microalgae that play a pivotal role in biological and geochemical marine cycles. These microorganisms are at the basis of the trophic chain and their lipids are essential components (e.g. eicosapentaenoic acid, EPA) of aquatic food webs. Galactolipids are the primary lipid components of plastid membranes and form the largest lipid family of diatoms. As source of polyunsaturated fatty acids (PUFAs), these compounds are also involved in the synthesis of lipoxygenase (LOX) products such as non-volatile oxylipins and polyunsaturated aldehydes. Here, we report the first identification of two genes, namely PmLAH1 and PaLAH1, coding for lipolytic enzymes in two diatoms of the genus Pseudo-nitzschia. Functional and modeling studies evidence a patatin-like domain endowed with galactolipase and phospholipase activity at the C-terminus of both proteins. Homologues of Pseudo-nitzschia LAH1 genes were retrieved in other diatom species so far sequenced in agreement with conservation of the functional role of these proteins within the lineage. •Galactolipids are key components of chloroplast membranes and major lipid class in marine diatoms under natural growth conditions.•By targeting glycolipids and phospholipids, different patatin-like proteins relay a growing number of important biological functions in the development and pathology of photosynthetic organisms.•LAH1 of P. arenysensis and P. multistriata contain the first patatin-like sequence identified in diatoms. The putative genes showed good sequence conservation in the patatin-like PLA (GxSxG) motif and catalytic dyad, as well as high similarity in the domain region (in the protein secondary structure level) with the patatin from Solanum cardiophyllum.•Homologous LAH1 genes are also found in the genomes or transcriptomes of any other diatom so far sequenced. The phylogenetic analysis showed that PmLAH and PaLAH formed a monophyletic group with other secondary red endosymbionts.•In analogy with plants, LAH1 is involved in the biosynthesis of oxylipins and may control the physiological role of these chemical mediators in diatom cells. Analogies with other microalgae and overexpression of LAH1 in P. tricornutum (XP_002180454.1) under N-starvation support also a possible role of this class of enzymes in galactolipid metabolism and lipid remodelling of diatoms.