Cellular Metabolic Modulation During The Resting Cells Formation In Marine Diatom Thalassiosira Pseudonana

Diatom resting stage cell(including resting cell and resting spore)formationhas been considered as an effective strategy for maintaining diatom populations to cope withadverse conditionsin marine ecosystems.One of outstanding characteristics of resting stage cells is producing heavily silicified frustules,which increasing the sinking rates of the cells to sediment and keep alive.However,the cellular responses and metabolic modulation involved in resting stage cells formation in diatoms are still unknown.In the present study,the celluar responses and mechanisms related to cell wall synthesis,oxidative stress response,and energy supply during the resting cells formation in marine diatom Thalassiosira pseudonana were comprehensively analyzed through physiological measurement,biochemical detection,and transcriptome analysis.The results will provide us a new insight of the detailed metabolism modulation and adaptive strategy during resting cells formaion in T.pseudonana.T.pseudonanacells were induced to form resting cells under dark and 4 0C for 12 weeks(three months).During the resting cells formation,the cell density of T.pseudonana decreased rapidly coupled with the inhibition of photosynthesis indicated by the decreased value of Fv/Fm.The neutral lipidaccumulation was obviously increasedduring 6 to 8 weeks,then decreased after 8 weeks Silicon content of cell wall in resting cellswas three times higher than that of vegetatvie cellsat the end of 12 weeks.Intracellular ROS content was very high in the cells that were ready to form resting cells,significantly higher than normal cells.However,the percentage of T.pseudonana cells which underwentprogrammed cell death(PCD)was less during resting cell formationCellular response and genes involved in celluar modulation during resting cells formation were investigated using transcriptomc analysis.A total of 11882 unique genes were identified in six time points(0,4?6?8?10?12weeks)and 4840 genes with significant expression levels were selected.Among them,the genes related to cell wall formation,such as CinW2,Si14,and polyamine synthesis-related enzymes,were significantly up-regulated,indicating their roles in heavy silicification.At the same time,functional analysis of the gene clusters co-expressed with CinW2 and Sil 4 revealed a newinsight into relevant regulation involved in silicon metabolism.Transcriptional data of oxidative stress related genes showed thatxanthophyll cycle was employed for cell repairand superoxide dismutase(SOD)may play an important role in ROS removal to improve the survival.At the same time,the analysis of genes related to fatty acid metabolism showed the role of neutral lipid in the energy supply for resting cells.Ours results provide us a new insight into survival mechanism and unique stress adaptation strategy for resting cells,which ensured the survival advantage of diatom and enhance our understanding of the role of diatom resting cells in biogeochemical cycles of silicon and carbon.