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Chloroplast lipid transfer processes in Chlamydomonas reinhardtii involving a TRIGALACTOSYLDIACYLGLYCEROL 2 ( TGD 2) orthologue
Author(s) -
Warakat Jaruswan,
Tsai ChiaHong,
Michel Elena J. S.,
Murphy George R.,
Hsueh Peter Y.,
Roston Rebecca L.,
Sears Barbara B.,
Benning Christoph
Publication year - 2015
Publication title -
the plant journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 3.058
H-Index - 269
eISSN - 1365-313X
pISSN - 0960-7412
DOI - 10.1111/tpj.13060
Subject(s) - chlamydomonas reinhardtii , chlamydomonas , chloroplast , chloroplast membrane , biology , endoplasmic reticulum , biochemistry , mutant , microbiology and biotechnology , thylakoid , gene
Summary In plants, lipids of the photosynthetic membrane are synthesized by parallel pathways associated with the endoplasmic reticulum ( ER ) and the chloroplast envelope membranes. Lipids derived from the two pathways are distinguished by their acyl‐constituents. Following this plant paradigm, the prevalent acyl composition of chloroplast lipids suggests that Chlamydomonas reinhardtii (Chlamydomonas) does not use the ER pathway; however, the Chlamydomonas genome encodes presumed plant orthologues of a chloroplast lipid transporter consisting of TGD ( TRIGALACTOSYLDIACYLGLYCEROL ) proteins that are required for ER ‐to‐chloroplast lipid trafficking in plants. To resolve this conundrum, we identified a mutant of Chlamydomonas deleted in the TGD 2 gene and characterized the respective protein, Cr TGD 2. Notably, the viability of the mutant was reduced, showing the importance of Cr TGD 2. Galactoglycerolipid metabolism was altered in the tgd2 mutant with monogalactosyldiacylglycerol ( MGDG ) synthase activity being strongly stimulated. We hypothesize this to be a result of phosphatidic acid accumulation in the chloroplast outer envelope membrane, the location of MGDG synthase in Chlamydomonas. Concomitantly, increased conversion of MGDG into triacylglycerol ( TAG ) was observed. This TAG accumulated in lipid droplets in the tgd2 mutant under normal growth conditions. Labeling kinetics indicate that Chlamydomonas can import lipid precursors from the ER , a process that is impaired in the tgd2 mutant.