Xiaoxu Li

Lysine malonylation (Kmal) is an evolutionarily conserved post-translational modification (PTM) that has been demonstrated to be involved in cellular and organismal metabolism. However, the role that Kmal plays in response to drought stress of the terrestrial cyanobacteria N. flagelliforme is still unknown. In this study, we performed the first proteomic analysis of Kmal in N. flagelliforme under different drought stresses using LC-MS/MS. In total, 421 malonylated lysine residues were found in 236 different proteins. GO and KEGG enrichment analysis indicated that these malonylated proteins were highly enriched in several metabolic pathways, including carbon metabolism and photosynthesis. Decreased malonylation levels were found to hinder the reception and transmission of light energy and CO₂ fixation, which led to a decrease in photosynthetic activity. Kmal was also shown to inhibit the flux of the TCA cycle and activate the gluconeogenesis pathway in response to drought stress. Furthermore, malonylated antioxidant enzymes and antioxidants were synergistically involved in reactive oxygen species (ROS) scavenging. Malonylation was involved in lipid degradation and amino acid biosynthesis as part of drought stress adaptation. This work represents the first comprehensive investigation of the role of malonylation in dehydrated N. flagelliforme, providing an important resource for understanding the drought tolerance mechanism of this organism.

Nostoc flagelliforme is a kind of terrestrial edible cyanobacteria with important ecological and economic value which has developed special mechanisms to adapt to drought conditions. However, the specific mechanism of lipidome changes in drought tolerance of N. flagelliforme has not been well understood. In this study, the ultra-high-performance liquid chromatography and mass spectrometry were employed to analyze the lipidome changes of N. flagelliforme under dehydration. A total of 853 lipid molecules were identified, of which 171 were significantly different from that of the control group. The digalactosyldiacylglycerol/monogalactosyldiacylglycerol (DGDG/MGDG) ratio was increased. The amount of wax ester (WE) was sharply decreased during drought stress, while Co (Q10) was accumulated. The levels of odd chain fatty acids (OCFAs) were increased under dehydration, positively responding to drought stress according to the energy metabolism state. In conclusion, the lipidomic data corroborated that oxidation, degradation, and biosynthesis of membrane lipids took place during lipid metabolism, which can respond to drought stress through the transformation of energy and substances. Besides, we constructed a lipid metabolic model demonstrating the regulatory mechanism of drought stress in N. flagelliforme. The present study provides insight into the defense strategies of cyanobacteria in lipid metabolic pathways.