Effects And Mechanism Of Water Stress On The Synthesis Of Flavonoids, Polysaccharides And Terpenoids In A

Cyclocarya paliurus is a rare tree species that survived the Quaternary glacial period.The leaves of C.paliurus are rich in flavonoids,polysaccharides and terpenoids,which have the functions of clearing away heat and detoxifying,lowering blood lipids,lowering blood sugar,lowering blood pressure,anti-aging,and enhancing immunity.In this study,two-year-old C.paliurus seedlings were used as the research object and water stress treatments were set up to result in mild treatment(W2),moderate treatment(W3)and severe treatment(W4).Sufficient water treatment were used as the control(W1).The physiological traits were measured and integrated transcriptomic and metabolomic analysis were used to explore the regulation mechanism of C.paliurus flavonoids,polysaccharides and terpenoids under different levels of water stress.The main findings of the study are as follows:(1)The relative water content,relative electrical conductivity,malondialdehyde content,chloroplast content,superoxide dismutase(SOD),peroxidase(POD)and catalase(CAT)in the leaves of C.paliurus physiological indicators were compared and analyzed.Results showed that moderate and mild water stress treatments can adjust photosynthetic system and antioxidant system of the seedlings of C.paliurus to cope with the oxidative damage,while the severe water stress treatment can not.(2)In the regulation pathway of flavonoids synthesis in C.paliurus,when seedlings were subjected to water stress,12 differential genes involved in 8 key enzymes of flavonoid synthesis,incudling CHS,CHI,F3 H,F3'H,FLS,DFR,ANS,and ANR all down-regulated,while the expression of 17 MYB transcription factors were closely related to the expression of key enzymes.A total of 171 differential metabolites of flavonoids were obtained under four different levels of water stress conditions,63 flavonoids accumulated a large amount under sufficient water conditions,while 61,18 and 29 flavonoids showed the maximum accumulation under mild,moderate and severe water stress conditions,respectively.(3)In the regulation pathway of polysaccharide synthesis in C.paliurus,a total of 42 differential key genes involved in the monosaccharide synthesis in C.paliurus were found,and the expression of 16 kinds of enzyme activities was closely related to them.Fructose 6-phosphate,an important intermediate in the formation of activated monosaccharides,is dependent on the regulation of fructokinase(scr K).The expression of Scr K-related genes was up-regultaed under severe water stress,which may lay a good foundation for the accumulation of polysaccharides under water stress conditions.(4)In the regulation pathway of terpenoid synthesis in C.paliurus,when seedlings were under water stress,the expression of 11 genes involved with 7 key enzymes of terpenoid synthesis,including GGPS,PCME,HMGCR,MVD,LUP2,LUP3,and TPS21,were highest under water stress conditions.The expression of key enzymes is closely related to four types of transcription factors,AP2,b ZIP?1,MYB and WRKY.A total of 44 terpenoid metabolites were obtained under four different levels of water stress conditions.Among them,6 terpenoids were hightest under adequate water conditions,13,12 and 13 terpenoids were highest under mild,moderate and severe water stress conditions.The research results can provide a theoretical basis for the cultivation of the high secondary metabolite C.paliurus.