Effects Of Drought Stress And Rehydration On Reactive Oxygen Species Metabolism In Camellia Sinensis Based On Transcriptome And Metabolomics

Moisture is a major factor influencing the growth and development of crops.Due to global warming and the increasing demand for water for non-agricultural use,breeding drought-tolerant varieties is an important target for crop breeders.Tea plant[Camellia sinensis（L.）O.Kuntze.]is one of the most important economic crops in China,which likes warmth and moisture,and has high requirements for moisture.Hunan province is one of the cities with the most serious drought in southern China.Due to the influence of climate and geographical location,seasonal drought mainly occurs in summer and autumn.The seasonal drought in Hunan province seriously affects the growth and development,yield and quality of summer-autumn tea,resulting in a great decrease in the economic benefits of tea production.Therefore,it is of great significance to study the mechanism of drought resistance mediated by reactive oxygen species（ROS）metabolism in tea plants under drought and rehydration treatment.In order to explore the regulation of ROS metabolism and the mechanism of drought resistance mediated by ROS metabolism in tea plants under drought and rehydration treatment,one-year-old potted seedlings of tea plant strain‘9808’were treated with natural drought and rehydration.Firstly,phenotypic observation,scanning electron microscope observation,leaf chlorophyll fluorescence parameters,photosynthetic pigment content,relative water content,ROS content,malondialdehyde content and antioxidant enzyme activity were used to analyze the effects of drought and rehydration treatment on the morphological structure and physiological characteristics of tea plants.The transcription and metabolite responses of ROS metabolism in tea plant under drought and rehydration treatment were studied by transcriptome and metabolomics.The main results are as follows:（1）The results of phenotypic observation and physiological index determination showed that under drought treatment,tea leaves gradually wilted and drooped,and even scorched spots appeared;stomatal length,width and opening decreased gradually,stomatal density increased significantly in the later stage of drought treatment;relative water content,Fv/Fm and Fv/Fo decreased gradually,photosynthetic pigment did not change significantly;H₂O₂ and MDA content increased gradually,and O₂·^-content increased significantly in the later stage of drought treatment.Except for GPX activity,the activities of SOD,APX,DHAR,MDHAR,GR and CAT in antioxidant enzymes increased at first and then decreased.After rehydration,tea seedlings recovered to erect,stomatal opening decreased significantly,stomatal density significantly increased,H₂O₂ content and SOD activity significantly increased,and other indexes returned to the pre-drought level.（2）The transcriptome results showed that GOX1,ACX1,ACX2,ACX3,PAO2,UOX,RBOHD,Cu AO1,GER3,GLP4,RCAR1 and RCAR3 genes involved in ROS production were significantly up-regulated under drought treatment,and Cu AO1 genes were significantly up-regulated after rehydration.PLDα1,PIP2;1,CDPK5,MEKK1,OXI1 and ANP1 genes participated in ROS signal transduction were significantly up-regulated under drought treatment,and PIP2;1 and OXI1 genes were significantly up-regulated after rehydration.Ndh T,Pns L4,Pns L5,PGR5,RCA,PGLP1,PGLP2,HPR3,SGAT,GOX1,GDCH2,HPR2,NDB2,NDC1,AOX1A,AOX2,UCP1 and UCP3 genes involved in the energy dissipation pathway were significantly up-regulated under drought treatment and returned to the pre-drought level after rehydration.CSD1,MSD1,CCS,GPX4,GPX6,APX1,APX4 and GR1 genes related to antioxidant enzymes were significantly up-regulated under drought treatment,while CSD2,APX6 and DHAR3 genes were significantly down-regulated,and MSD1 gene was significantly up-regulated after rehydration.（3）Metabolomics results showed that most DEMs of amino acids and their derivatives,sugars and alcohols,phenolic acids,tannins,lignans,coumarins and alkaloids were significantly up-regulated during drought treatment,such as L-theanine,γ-aminobutyric acid,L-proline,D-glucose,inositol,caffeic acid,ferulic acid,pinoresinol,theaflavin,theaflagallin and indole.After rehydration,L-theanine,gallic acid,ferulic acid,theaflagallin and putrescine were significantly up-regulated as compared with those before drought treatment.A small part of flavonoid DEMs were significantly down-regulated in the early stage of drought treatment,but a large number of flavonoid DEMs were significantly up-regulated in the later stage of drought treatment,such as epicatechin gallate,kaempferol and eriodictyol,while most flavonoid glycosides were significantly down-regulated.After rehydration,DEMs such as didymin,phloretin and kaempferol were significantly up-regulated,while naringenin,pinobanksin and naringenin chalcone were significantly down-regulated.Taken together,ROS in peroxisome under drought treatment was mainly produced by photorespiration,fatty acidβ-oxidation and purine metabolism in tea plant.Extracellular ROS production was mainly mediated by RBOH,Cu AO and Ox O.ROS is actively involved in drought resistance signal transduction in tea plants under drought treatment.Tea plants reduce ROS production mainly through PGR5/PGRL1-dependent CET,AOX,UCP and ND pathways under drought treatment.Most genes encoded antioxidant enzyme in tea plants respond positively to drought stress to remove excessive ROS and maintain cell redox level.Tea plants accumulate osmotic substances such as amino acids and sugars under drought stress to reduce ROS production,and accumulate a large number of antioxidants to remove excess ROS.The accumulation of flavonoids in tea plants in the late stage of drought stress may be due to the inhibition of antioxidant enzyme activities.