The metabolic survival strategy of marine macroalga Ulva prolifera under temperature stress

Ulva prolifera is a marine macroalga with medicinal and edible potential, but Ulva is also the causative genus behind undesirable green tides which cause serious adverse effects on coastal ecology and the environment. A strong relationship exists between U. prolifera blooms and ambient temperature; however, the metabolic mechanism involved is still largely unclear. To assess the metabolic changes in U. prolifera in response to temperature stress, the metabolic profile of U. prolifera was analyzed by gas chromatography-mass spectrometry (GC-MS), and a total of 67 compounds were identified. The metabolic profiles of U. prolifera cultured under high-and low-temperature treatments were significantly different from each other, as revealed by principal component analysis (PCA) and orthogonal partial least squares discriminant analysis (OPLS-DA). Twenty-four metabolites, including sugars and amino acids, accumulated under high-temperature stress (HTS) compared with those in the control group, while the levels of 9 and 6 metabolites significantly increased and decreased, respectively, under low-temperature stress (LTS). The galactose, starch/sucrose, and alanine/aspartate/glutamate metabolic pathways were changed under HTS, while the tricarboxylic acid cycle and starch/sucrose, tyrosine, and arginine/proline metabolism were involved in the LTS response. In addition, the metabolic network involved in temperature stress was further constructed. To the best of our knowledge, this is the first study to reveal metabolic shifts in U. prolifera in response to temperature stress and its results provide important insights into the mechanisms involved in the tolerance of U. prolifera to temperature stress and a basis for further research on green tide blooms.