Thylakoid Development and Galactolipid Synthesis in Cyanobacteria

Abstract

Cyanobacteria carry out oxygenic photosynthesis and share many features with chloroplasts, including thylakoid membranes, which are mainly composed of membrane lipids and protein complexes that mediate photosynthetic electron transport. Although the functions of the various thylakoid protein complexes have been well characterized, the details underlying the biogenesis of thylakoid membranes remain unclear. Galactolipids are the major constituents of the thylakoid membrane system, and all the genes involved in galactolipid biosynthesis were recently identified. In this chapter, I summarize recent advances in our understanding of the factors involved in thylakoid development, including regulatory proteins and enzymes that mediate lipid biosynthesis.

Thermoacclimation and genome adaptation of the membrane lipidome in marine Synechococcus

“…A possible candidate is a membrane protein possessing a PA phosphatase‐like domain (Cyanorak cluster CK_0000099). The diacylglycerol produced is then used as a substrate for the synthesis of MGlcDG, which in cyanobacteria, is further epimerized into MGDG (Awai, ). In many freshwater cyanobacterial strains, the MGlcDG epimerase is encoded by the mgdE gene (Awai et al ., ; Sato, ), which includes a C‐terminus Rossmann‐fold domain and a fatty acid hydroxylase at the N‐terminus, the function of which remains unclear (Awai, ).…”

Configuration of the sugar head of glycolipids in thylakoid membranes

“…, and then its glucose moiety is epimerized to galactose to form MGDG (Feige et al, 1980;Sato and Murata, 1982b;Awai, 2016 Epimerase, encoded by mgdE, is the other enzyme involved in the MGDG synthetic pathway in cyanobacteria. Epimerase is responsible for converting GlcDG into MGDG (Awai et al, 2014) by isomerizing glucose into galactose at the C4 hydroxyl group (Sato, 2015;.…”

“…Furthermore, it proved that GlcDG can replace the functions of galactolipids as a bulk constituent of thylakoid membranes (Awai et al, 2014;Awai, 2016). Several cyanobacteria species such as Gloeobacter violaceus, Thermosynechococcus elongatus, and Acaryochloris marina do not possess mgdE.…”

“…In Synechococcus, as described above, αβDGDG is essential. αβDGDG synthase in cyanobacteria (DgdA) has strict substrate specificity and utilizes only βMGDG (Awai, 2016), suggesting that αMGDG cannot be a substrate for DgdA. Thus, it is also possible that αMGDG could not complement the mgdA mutation because of the substrate specificity of DGDG synthase.…”

“…We also describe the physiological relevance of galactolipids and the attempts that have been made to complement the functions of these lipids by introducing heterologous glycolipid synthesis genes into photosynthetic organisms, especially cyanobacteria. For further details about these related topics, please refer to the following reviews: evolution of galactolipid synthesis in photosynthetic organisms Sato and Awai, 2016); biogenesis of thylakoid membranes (Rast et al, 2015;Awai, 2016); glycolipids in plants and bacteria (Hölzl and Dörmann, 2007).…”