| The tea plant(Camellia sinensis),a member of the genus Camellia Sinensis in the Camelliaceae family,is an important cash crop.Tea plants like warm and humid climate,and the best growth temperature is 20℃-25℃.China is the origin of tea,and is also the earliest country that discovered,utilized and planted tea in the world.Due to global warming,the summer temperature is gradually rising and extreme weather occurs frequently,which seriously affects the yield and quality of tea.Therefore,improving the resistance of tea plant has become one of the research hotspots.Trehalose,also known as leaky fucose,plays an important role in the life activities of living organisms and is one of the main sources of maintaining life activities.Currently,exogenous trehalose has been applied to improve heat tolerance.However,the role of trehalose in tea plants is still unclear.In this study,Tieguanyin was used as experimental material to spray trehalose on tea seedlings treated with high temperature stress,to determine the physiological characteristics of tea seedlings,and to explore the physiological and molecular mechanism of exogenous trehalose affecting tea trees under high temperature stress by using a transcription and metabolome technology system.The main results are as follows:1.Influence of exogenous trehalose on physiological characteristics of the tea plantThe seedlings were exposed to high temperature(light for 12 h,temperature 38℃;After dark for 12 h,temperature 29 ℃)for 2 days.the leaves were sprayed with clear water,2.5,5 and 10 mmol/L exogenous trehalose.Then the leaves of the second and third leaves of the above treated tea seedlings were sampled at 0 h,12 h,24 h,36 h and 48 h,and the physiological indexes of the leaves were measured.The results showed that exogenous trehalose increased the activities of superoxide dismutase(SOD)and peroxidase(POD)compared with clean water,suggesting that trehalose treatment enhanced the ability of scavenging reactive oxygen species(ROS)in tea leaves under high temperature stress.Treatment with 2.5 mmol/L and5 mmol/L trehalose significantly reduced malondialdehyde(MDA)content under high temperature stress,and increased proline and chlorophyll contents in tea leaves.Exogenous trehalose treatment also enhanced the content of soluble sugar in tea tree,and 2.5,5 and 10 mmol/L trehalose significantly increased the content of trehalose in leaves,indicating that trehalose treatment increased the content of sugar in tea tree leaves.In conclusion,exogenous trehalose has a protective effect on tea plants under high temperature stress.2.Transcriptional regulation analysis of exogenous trehalose in tea plants under high temperature stressBased on the analysis of the effects of exogenous trehalose on the physiology of tea plants,5 mmol/L trehalose had an effective protective effect on tea seedlings after 24 h of high temperature stress.Therefore,leaf samples from tea seedlings sprayed with water for 0 h of high temperature stress(CK),tea seedlings sprayed with water for 24 h of high temperature stress(T)and tea seedlings sprayed with 5 mmol/L trehalose for 24 h of high temperature stress(TT)were selected for transcriptomic sequencing to investigate the transcriptional regulatory mechanisms of alginate in tea plants under high temperature stress.The results showed that compared with the control group CK,the number of significantly up-regulated expressed genes in the T and TT groups were 527 and 470,and the number of significantly down-regulated genes were 1877 and 2793,respectively.In the TT vs.T comparison group,the number of significantly up-regulated and down-regulated genes was 508 and 109.In the comparison of exogenous trehalose and CK samples,301 genes not only responded to heat stress,but also responded to exogenous Tre signal.KEGG analysis showed that the genes were mainly enriched in MAPK signal pathway,plant hormone signal transduction,phenylpropyl biosynthesis,flavonoid biosynthesis,flavonoid and flavonol biosynthesis,and galactose metabolism.In-depth analysis of the above KEGG enrichment pathway found that: The expressions of Cs GOLS2,Cs RFS5,Cs PP2 C,Cs PYR/PYL,Cs HCT and Cs CYP75 A were significantly upregated in TT samples,suggesting that exogenous trehalosaccharids play an important role in inducing sugar metabolism,plant hormone signals,flavonoid biosynthesis and participating in high temperature stress.3.Analysis of metabolism regulation of tea tree under high temperature stress by exogenous trehaloseThe metabolic changes of CK,T and TT samples of Tieguyin tea seedlings were analyzed based on GC-MS and LC-MS non-targeted metabolome sequencing technology.The results showed that 94,95 and 101 DEM were identified by the GC-MS database in the three comparison groups(T vs.CK,TT vs.CK and TT vs.T).They were mainly organic oxygen compounds(29.47%),carbohydrates and their derivatives(13.79%)and fatty acids(9.72%).1117,956 and 1179 DEM were identified by LC-MS database,respectively.They were mainly pregnenolone esters(10.26%),organic oxygen compounds(9.67%),fatty acids(8.91%),polyketones(6.74%),carbohydrates and their derivatives(6.11%).KEGG enrichment analysis of differential metabolites in the three comparison groups showed that a total of 6 metabolic pathways were significantly enriched by GC-MS and 9 by LC-MS.In-depth analysis of KEGG revealed that exogenous trehalose caused changes in amino acids,sugars,flavonoids and other metabolites.4.Correlation analysis of exogenous trehalose on the transcriptome and metabolome of tea tree under high temperature stressThe KEGG enrichment pathway shared by differential genes and differential metabolites in the three comparison groups was analyzed.It was found that ABC transport was significantly enriched in T vs.CK,and alanine,aspartic acid and glutamic acid metabolism as well as cyano-amino acid metabolism were significantly enriched in TT vs.CK.Galactose metabolism was significantly enriched in TT vs.T.Further analysis of pathway differential genes and differential metabolite expression showed that Cs ABCC1,the main regulatory gene of ABC transport pathway,may cause the accumulation of amino acid and carbohydrate metabolites and participate in the response to high temperature stress.The accumulation of L-glutamate and L-glutamine may be related to the up-regulated expression of Cs ASNA,Cs GLT1 and Cs GS genes.In addition,the up-regulation of hydrothreose metabolite content may be influenced by the up-regulation of Cs GOLS and Cs RFS5 expression. |
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