Response to the CO2 concentrating mechanisms and transcriptional time series analysis of Ulva prolifera under inorganic carbon limitation

Ulva prolifera is a dominant species in green tides and has been affecting marine ecosystem for many years. Due to the low availability of CO₂ in the environment, U. prolifera utilizes the CO₂ concentrating mechanisms (CCMs) to increase intracellular inorganic carbon concentration. However, the transcriptional response mechanism and temporal changes of U. prolifera CCMs based on transcriptomics have not been thoroughly described. Therefore, we induced U. prolifera CCMs in a low CO₂ environment to explore the dynamic regulation of CCMs expression under inadequate inorganic carbon supply. The results showed that inorganic carbon limitation increased the inorganic carbon affinity of U. prolifera, upregulating CCMs. The first 24 h of inorganic carbon environmental changes were the most active period for U. prolifera's expression regulation. U. prolifera gradually achieved a new steady state by regulating metabolic processes such as nucleic acids, energy, and ethylene-activated signaling pathways. In the carbon fixation system of U. prolifera, there are characteristics of both biophysical and biochemical CCMs. After 24 h of inorganic carbon limitation, the biophysical CCMs becomes more effective under conditions of inorganic carbon depletion. This study aids in exploring the CCMs of U. prolifera and their evolution in response to environmental changes.