BACKGROUND: Algae have attracted attention as sustainable producers of lipid-containing biomass for food, animal feed, and for biofuels. Parachlorella kessleri, a unicellular green alga belonging to the class Trebouxiophyceae, achieves very high biomass, lipid, and starch productivity levels. However, further biotechnological exploitation has been hampered by a lack of genomic information. RESULTS: Here, we sequenced the whole genome and transcriptome, and analyzed the behavior of P. kessleri NIES-2152 under lipid production-inducing conditions. The assembly includes 13,057 protein-coding genes in a 62.5-Mbp nuclear genome. Under conditions of sulfur deprivation, lipid accumulation was correlated with the transcriptomic induction of enzymes involved in sulfur metabolism, triacylglycerol (TAG) synthesis, autophagy, and remodeling of light-harvesting complexes. CONCLUSIONS: Three-dimensional transmission electron microscopy (3D-TEM) revealed extensive alterations in cellular anatomy accompanying lipid hyperaccumulation. The present 3D-TEM results, together with transcriptomic data support the finding that upregulation of TAG synthesis and autophagy are potential key mediators of the hyperaccumulation of lipids under conditions of nutrient stress.

Bioimaging Center Graduate School of Frontier Sciences University of Tokyo 5 1 5 Kashiwanoha Kashiwa Chiba 277 8562 Japan

Center for Omics and Bioinformatics Graduate School of Frontier Sciences University of Tokyo 5 1 5 Kashiwanoha Kashiwa Chiba 277 8561 Japan

Department of Genetic Resources Technology Faculty of Agriculture Kyushu University Fukuoka Japan

Department of Integrated Biosciences Graduate School of Frontier Sciences University of Tokyo 5 1 5 Kashiwanoha Kashiwa Chiba 277 8562 Japan

Institute of Microbiology CAS Centre Algatech Laboratory of Cell Cycles of Algae Opatovický mlýn 379 81 Třeboň Czech Republic

Japan Science and Technology Agency CREST 5 1 5 Kashiwanoha Kashiwa Chiba 277 8562 Japan

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