Physiological Response And Gene Differential Expression Of Tea Plant To NaCl Stress

Tea plant[Camellia sinensis?L.?O.Kuntze]is one of the most important agricultural crops in many countries,and China has a long history and wide range of tea cultivation.Tea plant is a kind of perennial woody plants which prefer acidic soil,the most suitable soil pH for its growth is between 4.5 and 5.5.However,in many areas,the soil salinization degree is high,which caused serious influence on the growth of tea plant and tea quality.Therefore,it's of great significance to study the salt resistant mechanism of tea plant.In this research,we use tea cultivar“Longjingchangye”two-year seedlings as test materials,and a pot experiment was conducted to simulate the soil salinization environment.The photosynthetic index,SPAD value,MDA content,antioxidant activity and antioxidant content of tea plant under 200 mM NaCl stress were determined.At the same time,the tea cultivar"Pingyangtezao"one-year old hydroponic seedlings were used as materials for salt treatment and their shoots were collected for RNA extraction and transcriptome sequencing.The second generation high-throughput sequencing and bioinformatics analysis were conducted to study the response mechanisms on the level of gene transcription of tea plant under salt stress.The main results are as follows:1.Under high salinity stress,with the extension of stress time,the net photosynthetic rates of tea leaves were decreased,the stomatal conductance and transpiration rate showed a downward trend after rising,the intercellular CO₂ concentration was increased and the chlorophyll content was decreased.The malondialdehyde?MDA?content increased first,then decreased,and then increased which reached the highest at the third day of salt treatment.The POD,CAT and APX oxidase activities showed upward trends,but the activity of SOD was inhibited.The content of AsA and GSH increased under salt stress.The result shows that the photosynthesis of tea plant was inhibited under salt stress,and the membrane system was damaged,but part of the antioxidant enzymes and antioxidants can help eliminate free radicals and reducing lipid peroxidation.2.RNA-Seq technology was used to compare the transcriptomes from tea plants treated with and without NaCl and analyzed the differentially expressed genes?DEGs?.In total,150,257 unigenes were obtained that had average lengths of 680.40 nt,and 28,831 of these sequences were annotated in public databases.In addition,1769 DEGs were identified,including 947 up-regulated and 822 down-regulated ones.Many of these DEGs were involved in Ca²⁺signal transduction,the abscisic acid?ABA?pathway,and mitogen-activated protein kinase?MAPK?cascades.Many DEGs were also transcription factors and key functional proteins involved in salt resistance in tea plants;these genes constitute a regulatory network in response to salt stress.qRT-PCR analyses of 9 unigenes were performed to confirm the validity of the data,and the results were highly consistent with the RNA-Seq results.