RESUMO
Lysine lactylation (Kla) is a kind of novel post-translational modification (PTM) that participates in gene expression and various metabolic processes. Nannochloropsis has a remarkable capacity for triacylglycerol (TAG) production under nitrogen stress. To elucidate the involvement of lactylation in lipid synthesis, we conducted chromatin immunoprecipitation sequencing (ChIP-seq) and mRNA-seq analyses to monitor lactylation modifications and transcriptome alterations in Nannochloropsis oceanica. In all, 2057 genes showed considerable variation between nitrogen deprivation (ND) and nitrogen repletion (NR) conditions. Moreover, a total of 5375 differential Kla peaks were identified, including 5331 gain peaks and 44 loss peaks under ND vs NR. The differential Kla peaks were primarily distributed in the promoter (≤1 kb) (71.07%), 5'UTR (22.64%), and exon (4.25%). Integrative analysis of ChIP-seq, transcriptome, and previous proteome and lactylome data elucidates the potential mechanism by which lactylation promotes lipid accumulation under ND. Lactylation facilitates autophagy and protein degradation, leading to the recycling of carbon into the tricarboxylic acid (TCA) cycle, thereby providing carbon precursors for lipid synthesis. Additionally, lactylation induces the redirection of carbon from membrane lipids to TAG by upregulating lipases and enhancing the TCA cycle and ß-oxidation pathways. This research offers a new perspective for the investigation of lipid biosynthesis in Nannochloropsis.
RESUMO
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.