Acyl-acyl carrier protein pool dynamics with oil accumulation in nitrogen-deprived Chlamydomonas reinhardtii microalgal cells

Authors: Msanne, Joseph; SY VU, HIEU - University Of Nebraska; CAHOON, EDGAR - University Of Nebraska

Submitted to: Journal of the American Oil Chemists' Society
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/29/2021
Publication Date: 9/12/2021
Citation: Msanne, J.N., Sy Vu, H., Cahoon, E. 2021. Acyl-acyl carrier protein pool dynamics with oil accumulation in nitrogen-deprived Chlamydomonas reinhardtii microalgal cells. Journal of the American Oil Chemists' Society. 98(11):1107-1112. https://doi.org/10.1002/aocs.12539.
DOI: https://doi.org/10.1002/aocs.12539

Interpretive Summary: The interest in microalgae as a potential source for biofuel production is due to the high lipid content in some species, which is of great importance for the food and energy industries. However, for economic viability and sustainability it is essential to understand the basic biology of these organisms, particularly the effects of environmental stress on cellular metabolism and regulation of relevant pathways. Lipid metabolic pathways are not fully documented in microalgae and little is known about the formation, accumulation, or degradation of precursors that can be readily used as biodiesel. This study is the first in vivo characterization of intermediates in the fatty acid biosynthetic pathways in nitrogen-deprived Chlamydomonas reinhardtii cells. In order to gain a better understanding of these processes, we have examined the relative amounts of various intermediates produced, and investigated the correlations between those and the content and composition of relevant lipid portions. Our results confirmed that N deprivation played key roles in promoting fatty acid synthesis in C. reinhardtii, while the changes in the levels and utilization of various intermediates showed bias towards accumulation of longer-chain fatty acid groups. Our findings may also serve as a proxy for lipid metabolism and accumulation in oilseeds.

Technical Abstract: Microalgae are potential biofuel feedstocks for production of energy dense triacylglycerols (TAGs). Nitrogen deprivation is known to trigger microalgal TAG accumulation by upregulation of de novo fatty acid biosynthesis through chloroplast-localized Type II fatty acid synthases (FAS). To gain insights into the associated FAS regulatory mechanisms, we applied a recently reported liquid chromatography-mass spectrometry method to examine acyl-acyl carrier protein (ACP) pool compositional changes of the microalga Chlamydomonas reinhardtii over a nitrogen-deprivation time-course. We observed that acyl-ACP pools are highly enriched in acetyl-ACP in nutrient-rich media in photoheterotrophically-grown cells. Following shift to nitrogen deprivation, acetyl-ACP markedly decreased, and long-chain palmitoyl (16:0)-, stearoyl (18:0)-, and oleoyl (18:1)-ACPs progressively predominated in acyl-ACP pools in parallel with increases in fatty acid and TAG production. This study shows the utility of microalgal cells to study acyl-ACP pool dynamics to gain insights into plant fatty acid biosynthetic regulation and oil enhancement strategies.