Response To Salt Stress And Transcriptome Analysis Of Populus × Euramericana Cv.‘74/76’

With the continuous development of sequencing technology,the Illumina sequencing technology that with high throughput and wide detection range has become widely researchd in transcriptome analysis.And the transcriptomics technology can be used to comprehensively reveal the plant resistance molecular mechanism.In order to determine the formation of the poplar response to salt stress,further reveal the mechanism of resistance to salt stress and provide theoretical guidance for the salt tolerant breeding of poplar,the poplar 107 which is the main poplar clones in north plain and the transgenic poplar 107 with multiple genes were selected as the test material in this study.The response and tolerance to salt stress was analyzed by measuring the growth and physiological indexes.High throughput sequencing technology was used to analyze the transcriptome of poplar 107 seedlings under different salt concentrations treatments,part of physiological indicators were also determined to excavate salt resistance genes.The main results were as follows:(1)The growth and physiological indexes of poplar107 seedlings that treated with different concentrations of Na Cl showed that under a low salt concentration(3‰),the growth of poplar 107 seedlings was inhibited gently.Chlorophyll content and plasma membrane permeability were all increased slightly,while the net photosynthetic rate,PSII actual photosynthetic efficiency Y(II),and PSII electron transport rate were showing a small decline as a result of the salt damage.In summary,the Poplar 107 seedlings suffered lighty from the salt damage,and showd a better adaptability.While under a high salt concentration(6‰),the growth indexes of poplar 107 seedlings decreased significantly.The photosynthetic rate of PSII and the electron transport rate of PSII were significantly inhibited and then the poplar 107 seedlings suffered serious salt damage.(2)Transgenic poplar 107 showed a better adaptability under the low concentration salt stress of 3‰,and the salt tolerance was better than that of poplar 107.Under the high concentration salt stress of 6‰,the transgenic line and the control poplar 107 were all suffered a greater salt damage,and the transgenic line showed no advantage than poplar107.In addition,salt stress could enhance the expression of exogenous Bt gene and BADH gene.(3)Prior RNA quality detection,sequencing data filtering,quality assessment were made to ensured a high accuracy and credibility of the later transcriptome sequencing result;235 million clean reads were obtained after data filtering,and the total amount of data about 31.5G.Q20,Q30 values were higher than 99.08% and 96.70%,which ensured the reliability of late sequence alignment and analysis results.Then the sequencing data was maped to Populus trichocarpa Torr.&Gray genome,and the mapped efficiency up to64.561% ～ 70.69%;After screening the differentially expressed genes,pop3(3‰ Na Cl concentration treatment)and pop6(6‰ Na Cl concentration treatment)obtained 292 and3284 DEGs respectively,and also 199 co-expressed DEGs.Compared with the 3‰ low salt concentration treatment,there was a large number of stress inducible genes differentially expressed in poplar 107 under 6‰ high salt concentration treatment.The high specificity and reproducibility of q RT-PCR indicated that the transcriptome results were reliable.(4)GO notes and KEGG enrichment analysis results showed that the salt resistance mechanism of poplar 107 was different under different salt concentration treatment.Compared with a lower salt concentration treatment,the poplar 107 performed more salt tolerant metabolic pathways under a higher salt concentration treatment,of which includes the citric acid cycle(TCA cycle),terpenoids,flavonoids and biological synthesis flavonol biosynthesis,carotenoids,zeatin,calcium signal transduction pathway,Etc.In this study,we investigated the key genes affecting the electron transport of photosynthesis,and the key enzyme genes involved in the biosynthesis of glutathione and terpenoids in response to salt stress.(5)The study explored the key enzyme genes of poplar 107 in response to salt stress and found: Under a high salt concentration,Psb K and Psb Y protein synthesis genes significantly down regulated expression may be the main reason that the electron transfer efficiency of Pheo and QA decreased,which thereby affected the photosynthetic capacity.And the function of Psb R,Psb K,Psb Y proteins were related to electron transfer between Pheo and QA.GSH-Px and GST gene have great application potential in improving plant tolerance to abiotic stress.(6)Through the identification of gene alignment,52 TFs that closely related to salt stress were obtained,of which 24 TFs were new.The 52 TFs were all induced by salt stress,but the expression patterns were not consistent,its specific regulatory network and function need to be further verified.