Limited fatty-acid supply from the plastid and active catabolism of triacylglycerol prevent the accumulation of triacylglycerol in Coccomyxa sp. strain Obi grown under nitrogen-replete conditions

Limited fatty-acid supply from the plastid and active catabolism of triacylglycerol prevent the accumulation of triacylglycerol in Coccomyxa sp. strain Obi grown under nitrogen-replete conditions

The Coccomyxa sp. strain Obi is a unicellular green alga that accumulates >40% triacylglycerol (TAG) per cell dry weight under nitrogen (N)-limiting conditions. In this study, we analyzed the de novo synthesis of TAG under N-replete and N-limiting conditions using 14C tracers and quantitative rev...

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Bibliographic Details
Published in:Algal research (Amsterdam) Vol. 62; p. 102620
Main Authors: Oyama, Kaori, Matsuwaki, Izumi, Ito, Maika, Iwahori, Rei, Nagata, Haruka, Nakamura, Isuzu, Kondo, Ayaka, Kodaka, Akane, Fuseya, Yurika, Yamamoto, Haruka, Ueyama, Yui, Ide, Yoko, Kasai, Yuki, Harayama, Shigeaki, Kato, Misako
Format: Journal Article
Language:English
Published: Elsevier B.V 01-03-2022
Subjects:
Biofuels
Coccomyxa
Lipid biosynthesis
Microalgae
Triacylglycerol
PDAT
OPPP
LACS
TLC
Coccomyxa
N
LPAT
Triacylglycerol
DGDG
kBq
RT-qPCR
PUFA
DGAT
Microalgae
DAG
Biofuels
ACP
Bq
PC
CoA
GBq
Lipid biosynthesis
FAT
MGDG
TAG
FAX
MBq
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Summary:The Coccomyxa sp. strain Obi is a unicellular green alga that accumulates >40% triacylglycerol (TAG) per cell dry weight under nitrogen (N)-limiting conditions. In this study, we analyzed the de novo synthesis of TAG under N-replete and N-limiting conditions using 14C tracers and quantitative reverse transcription PCR (RT-qPCR) approaches. In cells grown under N-replete conditions, the incorporation of photosynthetically fixed 14C into TAG was <5% of that incorporated into polar lipids, whereas the incorporation of exogenous 14C-fatty acids into TAG was approximately 50% of that incorporated into polar lipids. These results demonstrated that enzyme activities that convert fatty acids to TAG are appreciably expressed under N-replete conditions; however low fatty acid supply limits the TAG synthesis in N-replete cells. In agreement with this inference, the expression of FAT1 that encodes acyl-ACP thioesterase, which releases free fatty acids from acyl-ACP, was poorly expressed under N-replete conditions but induced under N-limiting conditions. Meanwhile, pulse-chase labeling experiments demonstrated a significant turnover of TAG under N-replete conditions. Taken together, we propose that both the limited carbon flux into TAG and active catabolism of TAG prevented the accumulation of TAG under N-replete conditions, whereas the increased carbon flux into TAG and possibly decreased catabolism of TAG contributed to the enhanced accumulation of TAG under N-limiting conditions. Furthermore, pulse-chase experiments demonstrated that the rate of TAG synthesis was much slower than that of polar lipid synthesis under N-limiting conditions, partly because of the slow conversion of diacylglycerol to TAG. •Coccomyxa accumulated TAG under N-limiting (N−) but not N-replete (N+) conditions.•Enzymes converting fatty acids to TAG were active under both N− and N+ conditions.•A short supply of fatty acids resulted in low TAG accumulation under N+.•Acyl-ACP thioesterase that forms free fatty acid from acyl-ACP was induced under N−.•TAG underwent rapid turnover under N+.
ISSN:2211-9264
2211-9264
DOI:10.1016/j.algal.2021.102620