The Global Transcriptome Of Pyropia Haitanensis Under Salt Stress

Red algae Pyropia haitanensis is native to the subtropical zone of the South China coast and prefer to inhabit in the intertidal zone.With the change of the tide,P.haitanensis often suffer from high-and low-salt stress.P.haitanensis have been formed a strong salt tolerance,but the mechanism is not clear so far.In this study,P.haitanensis strain Z-61,selected by the Jimei University,was used as the experimental material.The global transcrip tome of P.haitanensis under high-and low-salt stress through high-throughput sequencing technology(RNA-Seq),combined with the physiological and biochemical investigations,can be used to select many key genes with regulatory function,and which will lays an important foundation for traditional breeding and/or genetic breeding of resistance varieties.The main experimental results are as follows:1.Under 100‰ salinity stress,the content of GSH and the activity of CAT increased with the increasing H2O2 content.A slight increase of ROS did not shown significant effect on the photosynthesis and membrane system of P.haitanensis.Under 110‰ salinity stress,the contents of GSH、APX and the activity of CAT increased in the first 4h and then declined.Then,the accumulation of a large amount of ROS resulted in severe damage to the photosynthetic and cell membrane of P.haitanensis.Acccording to transcriptome sequencing results:Under 100‰ salinity stress,P.haitanensis strengthened photosynthesis,improved carbon metabolism,and provided sufficient energy;accumulated betaine,proline,trehalose and other osmoprotectants to regulates osmotic pressure;synthesized expansion proteins to provide a platform for the assembly of carbohydrate components in the cell wall;used Na+as an osmoregulatory agent.Therefore,the algae can adapt to the salinity stress and it does not affect the survival of the algae.Under 110‰ salinity stress,P.haitanensis began to weaken photosynthesis and carbon metabolism;synthetized betaine,proline,trehalose and other osmotic adjustment substances to regulate osmotic pressure;synthetized glycoside hydrolase and pectin methylesterase inhibitors to inhibite the methylation of cell walls and maintaine cell wall integrity;pronounced the K+leakage and activated SOS1 to avoid the accumulation of Na+;activated heat shock proteins to repair or eliminate misfolded proteins.Therefore,the metabolic function of the algae was impaired and the growth was inhibited.2.Under 5‰ salinity stress,GSH,CAT and APX all play an important role.The content of GSH increased from 0 to 4 h,and the activity of CAT and APX remained at a relatively high level from 0 to 24 h,which resulted in a small amount of ROS accumulated in the cells,but did not affect photosynthesis and membrane systems of P.haitanensis.Under 0‰ salinity stress,CAT and APX played a major role in 0-8 hours,GSH played a major role in 8-24 hours,but they can not clean the ROS which causing severe oxidative damage to cell membrane and photosynthetic system.Transcriptome sequencing result shows:Under 5‰ salinity stress,P.haitanensis reduced photosynthesis and energy metabolism;accelerated the synthesis of expansion protein to cope with swelling of protoplasts;synthesized alpha-galactosidase to reduce intracellular osmotic pressure;triggered KAT protein channels to avoid ion imbalance caused by loss of K+.Then,P.haitanensis eventually sustained a normal growth under 5‰ salinity stress.Under 0‰ salinity stress,photosynthesis and energy metabolism were inhibited;heat shock proteins were activated to repair damaged proteins;glycosyltransferases synthesized cell wall cellulose and repaired damaged cell membranes;alpha-galactosidase reduced intracellular osmotic pressure;the channel protein genes were down-regulation and resulted in intracellular ion flocculation.Thus,0‰ salinity stress ultimately impaired the metabolic function of the algae.In conclusion,high salt stress enhanced the photosynthesis of algae,increased energy metabolism,and increased intracellular osmotic pressure by synthesizing proline,betaine,trehalose,etc.;low salt stress weakened the photosynthesis of algae,reduced energy metabolism,and reduced intracellular osmotic pressure by synthesizing α-galactosidase.Under 100 ‰ and 5 ‰ salinity stress,the cell wall was mainly composed of synthetic expansion proteins to adapt to the deformation caused by shrinkage or expansion of cells,and activated antioxidant to eliminate excessive ROS to ensure intracellular redox balance;Meanwhile,the protein synthesis and other metabolism were not significantly affected.However,Under salinity of 0‰ and 110‰,the expansion protein was damaged,and the cell wall was maintained by increasing activity of cell wall metabolic enzymes.Besides,the algae weakened the photosynthesis and synthetized a large amount of ROS,but could not activate antioxidant systems.Therefore,the algae suffer from the oxidative damage.In addition,the algae initiated heat shock proteins to repair damaged proteins.Therefore,although salinity of 0‰ and 110‰ caused more serious damage to the algae,the protection systems of the algae ensured that the algae can recovery to normal growth after rehydration.