Novel Insight of Nitrogen Deprivation Affected Lipid Accumulation by Genome-Wide Lactylation in Nannochloropsis oceanica

Lysine lactylation (kla) as a post-translational modification (PTM) is linked to chromatin remodeling and gene transcription. Nitrogen stress can induce triacylglyceride (TAG) accumulation in most microalgae. To reveal lipid synthesis from another layer, the 4D label-free proteome method was used to track lactylation modifications and protein expression profiles after 3 days of nitrogen deprivation in Nannochloropsis oceanica to analyze the function and prevalence of lactylation. Under nitrogen deprivation (ND) and nitrogen repletion (NR) cultivation conditions, we mapped the proteome and lactylome of proliferating microalgal cells. The results showed that there were 5203 proteins identified and 1245 proteins differentially expressed; among them, 664 were upregulated and 581 were downregulated. The N. oceanica strain also has a total of 868 lactylation sites, which were found on 379 proteins. The lactylated proteins were linked to biological activities as diverse as lipid metabolism, carbon fixation, photosynthesis, glycolysis, and the tricarboxylic acid (TCA) cycle and were found in various subcellular compartments. Under ND, 414 specific lactylation sites were found in 252 proteins. More interestingly, under ND vs NR, lactylation showed a significantly upregulated trend. This study provides a foundation for the future epigenetic enhancement of microalgal cells by providing the first dataset of lactylome in Nannochloropsis.