Recycling of the major thylakoid lipid MGDG and its role in lipid homeostasis in Chlamydomonas reinhardtii.

Masako Iwai,Kota Asami,Mie Shimojima,Yui Yamada-Oshima,Takashi Kanamori,Hideya Yuasa,Hiroyuki Ohta

doi:10.1093/plphys/kiab340

Masako Iwai, Kota Asami + Show 5 more

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https://doi.org/10.1093/plphys/kiab340

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Journal: Plant physiology	Publication Date: Jul 23, 2021
Citations: 12	License type: CC BY 4.0

Affiliation: Tokyo Institute of Technology

Abstract

Monogalactosyldiacylglycerol (MGDG), the most abundant lipid in thylakoid membranes, is involved in photosynthesis and chloroplast development. MGDG lipase has an important role in lipid remodeling in Chlamydomonas reinhardtii. However, the process related to turnover of the lysogalactolipid that results from MGDG degradation, monogalactosylmonoacylglycerol (MGMG), remains to be clarified. Here we identified a homolog of Arabidopsis thaliana lysophosphatidylcholine acyltransferase (LPCAT) and characterized two independent knockdown (KD) alleles in C. reinhardtii. The enzyme designated as C. reinhardtiiLysolipid Acyltransferase 1 (CrLAT1) has a conserved membrane-bound O-acyl transferase domain. LPCAT from Arabidopsis has a key role in deacylation of phosphatidylcholine (PC). Chlamydomonas reinhardtii, however, lacks PC, and thus we hypothesized that CrLAT1 has some other important function in major lipid flow in this organism. In the CrLAT1 KD mutants, the amount of MGMG was increased, but triacylglycerols (TAGs) were decreased. The proportion of more saturated 18:1 (9) MGDG was lower in the KD mutants than in their parental strain, CC-4533. In contrast, the proportion of MGMG has decreased in the CrLAT1 overexpression (OE) mutants, and the proportion of 18:1 (9) MGDG was higher in the OE mutants than in the empty vector control cells. Thus, CrLAT1 is involved in the recycling of MGDG in the chloroplast and maintains lipid homeostasis in C. reinhardtii.

Highlights

Monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in the photosynthetic membranes called thylakoids in cyanobacteria and chloroplasts of algae and plants and is involved in both photosynthesis and chloroplast development (Block et al, 1983; Shimojima et al, 1997; Kobayashi et al, 2009a; Shimojima and Ohta, 2011; Boudiere et al, 2014; Kalisch et al, 2016)
To reveal the flow of lipid biosynthesis in C. reinhardtii, we focused on MGMG produced in C. reinhardtii and isolated a lysophospholipid acyltransferase (LPLAT) (ScALE1) homolog, which we named C. reinhardtii Lysolipid Acyltransferase 1 (CrLAT1)
Identification of MGMG in C. reinhardtii Chlamydomonas reinhardtii CC-4533 cells grown in Tris–acetate–phosphate (TAP) medium were harvested, and their lipids were extracted and separated by 2D thin-layer chromatography (2D-TLC)

Summary

Introduction

Monogalactosyldiacylglycerol (MGDG) is the most abundant lipid in the photosynthetic membranes called thylakoids in cyanobacteria and chloroplasts of algae and plants and is involved in both photosynthesis and chloroplast development (Block et al, 1983; Shimojima et al, 1997; Kobayashi et al, 2009a; Shimojima and Ohta, 2011; Boudiere et al, 2014; Kalisch et al, 2016). The last step in MGDG synthesis occurs in plastid envelope membranes. This reaction is catalyzed by MGDG synthase, which transfers a galactosyl residue from UDP-galactose to the sn-3 position of sn1,2-diacylglycerol (DAG; Shimojima et al, 1997; Benning and Ohta, 2005; Shimojima and Ohta, 2011).

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