Plastid-associated galactolipid composition in eyespot-containing dinoflagellates: a review

Abstract

Relative to the large number of photosynthetic dinoflagellate species, only a select few possess proteinaceous, carotenoid-rich eyespots which have been demonstrated in other algae to act in phototactic responses. The proteins comprising the different categories of dinoflagellate eyespots are positioned in or near the peridinin-containing photosynthetic plastid membranes which are composed primarily of two galactolipids, mono-and digalactosyldiacylglycerol (MGDG and DGDG). Within eyespot-containing dinoflagellates, this arrangement occurs mostly in those with secondary plastids, although some dinoflagellates with tertiary plastids of diatom origin are known to possess eyespots. We here provide an examination of the MGDG and DGDG composition of eyespot-containing dinoflagellates with secondary, peridinin-containing plastids and tertiary plastids of diatom origin to address the fundamental question of whether eyespots and their component proteins and carotenoids are associated with alterations in galactolipid composition when compared to eyespot-lacking photosynthetic dinoflagellates. This is an important question because the dinoflagellate eyespot-plastid membrane system can be considered a more complicated and evolved state of plastid development. Included in this examination are data on the previously unexamined peridinin-and type A eyespot-containing dinoflagellate Margalefidinium polykrikoides, and the type D eyespot-containing, aberrant plastid "dinotom" Durinskia baltica. In addition, we have reviewed the galactolipid composition of algae from the Chlorophyceae, Cryptophyceae, and Euglenophyceae as a comparison to determine if algal classes apart from the Dinophyceae contain altered galactolipids in association with eyespots. We conclude that the presence of an eyespot in dinoflagellates and other algae is not associated with noticeable changes in galactolipid composition.

Galactolipid composition of the star‐shaped dinoflagellate Asterodinium gracile (Kareniaceae): presence of hexadecatetraenoic acid (16:4(n‐3))‐containing monogalactosyldiacylglycerol as the predominant galactolipid and chemotaxonomic closeness to Karenia mikimotoi as the only other known Kareniacean producer of this fatty acid

“…2010; Graeff et al . 2021; Leblond et al . 2022a); from this point forward, fatty acids will be abbreviated without their double bond position after their first listing within the text.…”

“…Outside of K. mikimotoi the 16:4 fatty acid is extremely rare in other dinoflagellates, having to our knowledge only been identified in the ‘dinotom’ Durinskia baltica (Levander) Carty and Elenor R. Cox (Graeff et al . 2021) and Lepidodinium chlorophorum (Elbrächter & Schnepf) Gert Hansen, Botes & Salas that has a green algal endosymbiont (Leblond and Lasiter 2009).…”

“…We earlier speculated that the presence of the 16:4 fatty acid in MGDG and DGDG could be the result of an earlier transfer of the genes responsible for its biosynthesis from a green alga (because green algae are known to produce this particular fatty acid), and/or there has been a possible plastid lipid contribution from a pelagophyte (see Leblond et al (2019) and discussion therein about a possible pelagophyte ancestry). Outside of K. mikimotoi the 16:4 fatty acid is extremely rare in other dinoflagellates, having to our knowledge only been identified in the 'dinotom' Durinskia baltica (Levander) Carty and Elenor R. Cox (Graeff et al 2021) and Lepidodinium chlorophorum (Elbrächter & Schnepf) Gert Hansen, Botes & Salas that has a green algal endosymbiont (Leblond and Lasiter 2009).…”

“…Much work has shown peridinincontaining dinoflagellates with a secondary plastid possess molecules of MGDG and DGDG with a different fatty acid complement than dinoflagellates with tertiary plastids that have an aberrant pigment composition. Specifically, peridinin-containing dinoflagellates have been observed to cluster according to whether their MGDG and DGDG molecules are dominated by C 20 /C 18 (sn-1/sn-2) or C 18 /C 18 forms, where the C 20 and C 18 fatty acids are represented by eicosapentaenoic acid (20:5(n-3)), octadecapentaenoic acid (18:5(n-3)), and octadecatetraenoic acid (18:4(n-3)) (Gray et al 2009;Leblond et al 2010;Graeff et al 2021;Leblond et al 2022a); from this point forward, fatty acids will be abbreviated without their double bond position after their first listing within the text. By contrast, aberrant plastid dinoflagellates in the family Kareniaceae examined thus far have been observed to possess C 16 and/or C 14 fatty acids in the sn-2 position, in addition to C 18 /C 18 forms (Leblond and Lasiter 2009;Leblond et al 2019; see description below).…”

Carbohydrate-Containing Low Molecular Weight Metabolites of Microalgae

“…Diatoms (the phylum Bacillariophyta), along with dinoflagellates, are the largest taxa of primary producers in the oceans. Structural studies on galactolipids from diatoms were initiated in 1993 [ 58 ]. The diatom Phaeodactylum tricornutum , which can exist in different morphotypes and change cell shape, predominately has the same classes of galactolipids (MGDG, DGDG and, in smaller amounts, SQDG) as other microalgae.…”