Physiological Response And Transcriptome Analysis Of Eurya Emarginata Seedlings Under Salt Stress

In an attempt to explore the mechanisms underlying salinity tolerance,enzymatic activity,and expression of genes involved in ionic,osmotic,and antioxidant responses of the typical coastal plant Eurya emarginata were examined under stressed conditions of 150 and 300 mmol/L NaCl for 35 days.Physiological and biochemical parameters were also assessed.Salt stress adversely affected the growth of E.emarginata,as evidenced by reduced fresh weight(FW),leaf water content(LWC),and chlorophyll a and b contents.The inhibition of growth could be attributed to an increase in malondialdehyde(MDA)and proline contents,and Na+ concentration,and a decrease in K+ uptake in the leaves of E.emarginata.MDA and proline contents,and Na+and K+concentrations were closely related to activities of H+-ATPase,pyrroline-5-carboxylate synthetase(P5CS),and praline dehydrogenase(PDH),and antioxidant enzymes such as superoxide dismutase(Cu/Zn-SOD),catalase(CAT),and glutathione peroxidase(GPx).The effects of the two NaCl concentrations on the fresh weight(FW)of different organs(leaves,stems,and roots)varied.A significant decrease in FW was recorded at 150 and 300 mmol/L NaCl,which was primarily due to a reduction in the weights of roots and leaves.Salt stress also affected photosynthesis,resulting in significantly decreased contents of chlorophyll a and b.Leaf water content(LWC)was significantly lower in leaves at 150 mmol/L NaCl in comparison to the control.With increased salinity,Na+ concentrations and the Na+/K+ ratio remarkably increased;however,K+Concentrations were reduced.MDA content,reflecting the average lipid peroxidation level,significantly increased with increasing salinity in the leaves of E.emarginata.A similar trend was found with proline content.However,low salinity(150mmol/L NaCl)did not significantly affect proline accumulation.High salinity(300 mmol/L NaCl)sharply inhibited the activity of enzymes,including Cu/Zn-Cu/Zn-SOD,CAT,GPx,H+-ATPase,and PDH.Low salinity also reduced the activity of Cu/Zn-SOD,CAT,and PDH,but increased that of H+-ATPase,and did not affect GPx.The differentially expressed genes were annotated and classified based on the KEGG pathways,with a total of 50 pathways identified.Photosynthesis,photosynthesis-antenna proteins,and ribosome pathways accounted for the highest proportion of the DEGs,and they are mainly from pathways that are associated with photosynthesis.Differential gene expression of ribosome pathways can affect energy supply and protein synthesis,affecting enzymes that participate in many reactions.Differential gene expression of photosynthesis,photosynthesis-antenna protein pathways will directly affect the synthesis of photosynthetic pigments,electron transfer,and other photosynthesis-related processes.The control genes of Cu / Zn-SOD and PDH were also down-regulated after 150 mmol / L sodium chloride stress for 35 days,but the concentration of Cu,Zn-SOD and PDH was lower,but the control of CAT,GPx,H+-ATPase The expression of P5 CS gene was not affected.This shows that at the molecular level,Eurya japonica has a physiological mechanism corresponding to the control mechanism,in the low salt stress when it can resist the impact of salt damage,a strong salt tolerance.The expression of Cu / Zn-SOD,CAT,GPx,P5 CS,H+-ATPase gene was down-regulated in the presence of high salt stress,and the expression of P5 CS gene was up-regulated.When the concentration of 300 mmol / L sodium chloride was inhibited,the expression of salt-tolerant genes was inhibited,and the growth and metabolism of Eurya sativa was blocked.Sequencing by transcription sequence of Eurya sativa,a large number of transcript sequences and Unigene sequences were obtained,and the Unigene library of Eurya sativa was assembled after assembly.The results showed that the differential gene expression of Eurya spp.Under the salt stress was up-regulated and down-regulated,and the expression was mainly under the control of the genome sequence.According to the Unigene library sequence,the GO function,COG annotation and KEGG annotation were used to obtain the corresponding function and metabolic pathway of each Unigene,which laid the foundation for the future research on genomics and molecular biology.In conclusion,our data reveal the underlying ionic,osmotic,and antioxidant mechanisms of the response to salt stress,at the molecular level,in the typical coastal plant E.emarginata.Although salt stress weakened the antioxidant defense system,the up-regulation of H+-ATPase and P5 CS and the down-regulation of PDH could confer salt tolerance to E.emarginata plants and thereby prevent possible injury due to oxidative stress.