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

Microalgae are potential biofuel feedstocks for production of energy-dense triacylglycerols (TAG). Nitrogen deprivation is known to trigger microalgal TAG accumulation by upregulation of de novo fatty acid (FA) biosynthesis through chloroplast-localized Type II FA 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 FA and TAG production. This study shows the utility of microalgal cells to study acyl-ACP pool dynamics to gain insights into plant FA biosynthetic regulation and oil enhancement strategies.