| Skeletonema is a typical diatom taxa,whicih is widely distributed in the global ocean and is one of the main contributors to marine primary production,playing important roles in material cycle,energy flow and information transmission of marine ecosystem.Skeletonema often forms large-scale red tides when the environmental conditions are suitable,which is an important bait and food source for marine fish,shrimp and shellfish.Nitrogen,phosphorus,and silicon are essential nutrients for cell growth of Skeletonema,their variations will affect the survival,growth and proliferation of Skeletonema in the ocean.Although there have been some studies on physiological and molecular mechanisms of Skeletonema in response to ambient nutrient changing but majority of then aer focused on a few species,and early classification of Skeletonema was chaos,so our understanding of Skeletonema in response to ambient nutrient changing is still lack or ambiguous.Therefore,there is an urgent need to study the response mechanism of Skeletonema to nitrogen,phosphorus and silicon stresses,which will have an important role in understanding the survival,distribution and ecological significance of Skeletonema in the ocean.In this thesis,we selected three typical Skeletonema species,Skeletonema dohrnii,Skeletonema tropicum,and Skeletonema costatum as research objects,and comparatively studied gene expression profiles of three Skeletonema species under nitrogen-,phosphorus-and silicon-depelet stresses using a transcriptome sequencing technology.We further identified and characterized differentially expressed genes and their biological processes,and revealed the physiological and molecular mechanisms of three Skeletonema species to nitrogen,phosphorus and silicon stress combined with physiological parameters analysis.The main results obtained are as follows:(1)44,071,49,366 and 38,545 genes were identified in the transcriptomes of S.dohrnii,S.tropicum,and S.costatum,respectively,under nitrogen stress condition.Compared with normal culture conditions,there were 24.03%,42.14%,and 36.99%genes presented differential expression;46,098,33,468 and 40,752 were identified in the transcriptomes of S.dohrnii,S.tropicum,and S.costatum,respectively,under phosphorus stress condition.Compared with normal culture conditions,there were 13.63%,37.53%,and 25.11%genes presented differential expression;44,812,36,408,45,581 were identified in the transcriptomes of S.dohrni,S.tropicum,and S.costatum under silicon stress.Compared with normal culture conditions,there were 28.21%,30.34%,and 25.53%genes presented differential expression.Under nitrogen stress,photosynthesis,carbon metabolism,glycolysis and other processes were downregulated;under phosphorus stress,up-regulated photosynthesis-antenna protein,glycolysis,unsaturated fatty acids and ribosomes were only enriched in S.dohrnii;under silicon stress,photosynthesis was down-regulated and glycolysis was upregulated only in S.tropicum;(2)Under nitrogen stress condition,the three Skeletonema species could enhance the transport of nitrate in the environment and the hydrolysis of intracellular nitrogencontaining compounds to obtain nitrogen source.Nitrogen stress inhibited cell growth of three Skeletonema species,arresting cell cycle at the G1 phase,but enhanced the production process in the mitochondria,the hydrolysis of phospholipids,the synthesis of triacylglycerols and fatty acids which not only provided the energy but also increased defensive ability.Under nitrogen stress,hydrolyzation of nitrogen-containing compounds in S.tropicum cells was more active than that in the other two Skeletonema species,and more nitrogen source and energy were also obtained by enhancing ammonium transport,urea transport and decomposition,and triacylglycerol hydrolysis.In addition,four types of stress kinases,glutamine synthetase,6-phosphofructokinase 1,glyceraldehyde 3-phosphate dehydrogenase,and 26S proteasome,which enhance resistance to abiotic stress,were all highly expressed in S.tropicum,indicating that S.tropicum had higher nitrogen requirement and was more sensitive to nitrogen stress than the other two Skeletonema species;(3)Under phosphorus stress condition,three Skeletonema species enhanced inorganic phosphate transport,utilization of organic phosphorus and the lipids without phospholipids,thereby alleviating the need for phosphorus.Phosphorus stress inhibited cell growth of three Skeletonema species,arresting cell cycle at the G1 phase.By enhancing the synthesis of triacylglycerols,fatty acids,and proteasomes,the cells stored more energy and enhanced defense capability.Under phosphorus stress.S.dohrnii presented more efficient phosphate transport and utilization of organic phosphorus than the other two Skeletonema species.In addition,S.dohrnii had a stronger ability to regulate photosynthesis and glycolysis than the other two Skeletonema species in response to phosphorus stress.In the phosphorus-deficient seawater,S.dohrnii had an advantage in competing phosphorus sources than the other two species,and had a strong phosphorus and adaptive ability to low response,which made it easyily to become dominant species;(4)Under silicon stress condition,the three Skeletonema species enhanced the silicate transport capacity and the utilization of organic nitrogen and phosphorus,and inorganic phosphorus transport,so that the cells could obtain more nutrients for growth.Under silicon stress,cell growth of three Skeletonema species was inhibited,the cell cycle was arrested at the G1 phase and the cells could not form a normal siliceous cell wall,thsu,the cells absorbed light energy more easily,which might enhance the reaction center process of PSII and mitochondria ATP synthesis.Under silicon stress,S.tropicum enhanced the intracellular silicate transport and glycolysis process to alleviate the stress.It also increased the reaction process in PSII,triacylglycerol hydrolysis,and expression of multiple kinases to obtain more energy and defense capability,indicating that S.had higher silicon requirement and was more sensitive to silicon stress than the other two Skeletonema species. |
PDF Full Text Request