Lipids of Pedinomonas minor, Pedinomonas sp., Pyramimonas parkeae, Pyramimonas obovata: A Quest to Reconcile These Tertiary and Secondary Plastid Ancestors of the Dinoflagellate Lepidodinium chlorophorum and Euglenid Euglena gracilis.

Abstract

The goal of this study was to investigate the plastid origins of the only green-pigmented dinoflagellate genus, represented by Lepidodinium chlorophorum, and the evolutionary model euglenid Euglena gracilis. Intact forms of mono- and digalactosyldiacylglycerol (MGDG and DGDG, respectively) present in the thylakoid membrane of the green algae Pedinomonas minor and Pedinomonas sp., putative plastid ancestors of L. chlorophorum, and Pyramimonas parkeae and Pyramimonas obovata, putative plastid ancestors of E. gracilis, were elucidated via positive-ion mode electrospray ionization/mass spectrometry (ESI/MS) and ESI/MS/MS. I hypothesized that P. minor and Pedinomonas sp. would bear forms of MGDG and DGDG similar to forms of MGDG and DGDG present in L. chlorophorum, and P. parkeae and P. obovata would share homology with forms present in E. gracilis. All four species produced abundant forms of C18/C16 (sn-1/sn-2 regiochemistry) MGDG and scarce forms of C18/C16 DGDG. Specifically, Pedinomonas sp. and P. minor possessed 18:3/16:4 MGDG as the dominant galactolipid, which relates to a prior observation that L. chlorophorum produces the 16:4 fatty acid at the sn-2 position of both MGDG and DGDG. P. parkeae and P. obovata also possessed 18:3/16:4 MGDG and DGDG, but unlike the Pedinomonas pair, the Pyramimonas and Euglena pair was almost an exact match to each other. I also examined sterols of Pedinomonas and Pyramimonas. Pedinomonas did not produce any sterol similar to L. chlorophorum but Pyramimonas produced poriferasterol, a sterol found in E. gracilis.