CrABCA2 Facilitates Triacylglycerol Accumulation in Chlamydomonas reinhardtii under Nitrogen Starvation
Sunghoon Jang1,6, Fantao Kong3,6, Jihyeon Lee2,6, Bae Young Choi2, Pengfei Wang4, Peng Gao4, Takashi Yamano5, Hideya Fukuzawa5, Byung-Ho Kang4, and Youngsook Lee2,*
1Department of Life Sciences, Pohang University of Science and Technology, Pohang 37673, Korea, 2Integrative Biosciences and Biotechnology, Pohang University of Science and Technology, Pohang 37673, Korea, 3School of Bioengineering, Dalian University of Technology, Dalian 116024, China, 4Cellular and Molecular Biology Program, State Key Laboratory of Agrobiotechnology, School of Life Sciences, The Chinese University of Hong Kong, New Territories, Hong Kong 999077, China, 5Graduate School of Biostudies, Kyoto University, Kyoto 606-8502, Japan, 6These authors contributed equally to this work.
Received November 7, 2019; Revised November 30, 2019; Accepted December 2, 2019.; Published online January 7, 2020.
© Korean Society for Molecular and Cellular Biology. All rights reserved.

ABSTRACT
The microalga Chlamydomonas reinhardtii accumulates triacylglycerols (TAGs) in lipid droplets under stress conditions, such as nitrogen starvation. TAG biosynthesis occurs mainly at the endoplasmic reticulum (ER) and requires fatty acid (FA) substrates supplied from chloroplasts. How FAs are transferred from chloroplast to ER in microalgae was unknown. We previously reported that an Arabidopsis thaliana ATP-binding cassette (ABC) transporter, AtABCA9, facilitates FA transport at the ER during seed development. Here we identified a gene homologous to AtABCA9 in the C. reinhardtii genome, which we named CrABCA2. Under nitrogen deprivation conditions, CrABCA2 expression was upregulated, and the CrABCA2 protein level also increased. CrABCA2 knockdown lines accumulated less TAGs and CrABCA2 overexpression lines accumulated more TAGs than their untransformed parental lines. Transmission electron microscopy showed that CrABCA2 was localized in swollen ER. These results suggest that CrABCA2 transports substrates for TAG biosynthesis to the ER during nitrogen starvation . Our study provides a potential tool for increasing lipid production in microalgae.
Keywords: ABC transporter, Chlamydomonas reinhardtii, endoplasmic reticulum, triacylglycerol accumulation
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31 December 2019 Volume 42,
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