Uncommon properties of lipid biosynthesis of isolated plastids in the unicellular red alga Cyanidioschyzon merolae

Abstract

Red algae are a large group of photosynthetic eukaryotes that diverged from green algae over one billion years ago, and have various traits distinct from those of both green algae and land plants. Although most red algae are marine species (both unicellular and macrophytic), the Cyanidiales class of red algae includes unicellular species which live in hot springs, such as Cyanidioschyzon merolae , which is a model species for biochemical and molecular biological studies. Lipid metabolism in red algae has previously been studied in intact cells. Here, we present the results of radiolabeling and stable isotope labeling experiments in intact plastids isolated from the unicellular red alga C. merolae . We focused on two uncommon features: First, the galactose moiety of monogalactosyldiacylglycerol was efficiently labeled with bicarbonate, indicating that an unknown pathway for providing UDP‐galactose exists within the plastid. Second, saturated fatty acids, namely, palmitic and stearic acids, were the sole products of fatty acid synthesis in the plastid, and they were efficiently exported. This finding suggests that the endoplasmic reticulum is the sole site of desaturation. We present a general principle of red algal lipid biosynthesis, namely, ‘indigenous C18 fatty acids are neither desaturated nor directly utilized within the plastid'. We believe that this is valid in both C. merolae lacking polyunsaturated fatty acids and marine red algae with a high content of arachidonic and eicosapentaenoic acids.

A cryptic plastid and a novel mitochondrial plasmid inLeucomyxa plasmidiferagen. and sp. nov. (Ochrophyta) push the frontiers of organellar biology

“…plasmidifera ; figure 5 and supplementary electronic material, table S5). However, a presently unknown mechanism of UDP-glucose synthesis may exist, as hypothesized for the plastid of the red alga Cyanidioschyzon melorae (Mori et al 2018), and we cannot rule out the possibility that it also operates in the Leuc. plasmidifera plastid.…”

Dynamism of Metabolic Carbon Flow of Starch and Lipids in Chlamydomonas debaryana

“…Rapid labeling of DGDG was found in the 2-h labeling experiments (Figure 3) as well as the 5-h labeling step of labeling and chase experiments (Figure 5). In many organisms, such as cyanobacteria (Sato and Murata, 1982), algae (Sato and Moriyama, 2007;Mori et al, 2019, in Cyanidioschyzon merolae, Sato, 1991 in Cryptomonas), and plants (Williams et al, 1975;Heemskerk et al, 1991), the acyl groups of DGDG are not readily labeled in typical labeling experiments for 1 or 2 h. We already demonstrated that the outer galactose of DGDG is preferentially labeled in cyanobacteria (Sato and Murata, 1982) and red algae (Sato and Moriyama, 2007). DGDG is synthesized by galactosylation of MGDG, which precludes direct acylation of newly synthesized fatty acids to DGDG.…”

“…Elongation is characterized biochemically and genetically, but the in vivo evidence of elongation is a fortunate result of using this alga. In a red alga, Cyanidioschyzon merolae, 16:0 was found to be exported from the chloroplast and elongated to 18:0 in the ER (Mori et al, 2019). In plants, fatty acids are nearly exclusively synthesized within the chloroplasts (mitochondrial fatty acid synthesis is a very minor activity), in which 16:0 is elongated to 18:0, which is then desaturated to 18:1.…”

The Unicellular Red AlgaCyanidioschyzon merolae—The Simplest Model of a Photosynthetic Eukaryote

“…In addition, evidence to date suggests that metabolic pathways are also likely very simple in C. merolae . Although the contents of C. merolae metabolites have not yet been extensively examined, recent studies have shown that, relative to other eukaryotes, the lipid profile in C. merolae is quite simple and appears to lack phosphatidylserine and cardiolipin ( Mori et al 2016 , Sato et al 2017 , Mori et al 2019 ). Collectively, the simple characteristics of C. merolae render it suitable for many diverse studies, as exemplified in the section below.…”