Metabolic Regulation Mechanism Of Anthocyanin Synthesis In The Pericarp Of Zipiphus Jujuba Mill Cv.’Lingwuchangzao’ Under Interaction Of Elevated Temperature And Drought Stress

Under the background of increasing global warming,precipitation in different regions has changed dramatically.Ningxia is located in the inland area of northwest China.,soil moisture evaporation and precipitation are not balanced,and the increase of atmospheric temperature leads to the soil drought becoming serious.In order to analyze the changes of anthocyanin synthesis gene expression level and anthocyanin metabolite accumulation in peel of jujube cultivar ’Lingwuchangzao’under elevated air temperature and drought stress,clarify the regulation mechanism anthocyanin synthesis metabolism.In this experiment,the six-year-old‘Lingwuchangzao’from Ningxia,including the fruits of white ripening stage(C),semi-red crisp ripe stage(Z)and full-red crisp ripe stage(Z)were used as experimental materials.The interactive treatment experiment of air temperature and drought was set up.The self-made open-top chamber were used to simulate the elevated air temperature environment,and the precision irrigation control system(ZGH-MI-C)were used to control soil water content.The air temperature set the natural air temperature(T1)and elevated air temperature T2=T1+(2.0±0.5℃).Three levels of drought were set:normal soil moisture(D1,70%-75%of field maximum water holding capacity),moderate drought(D2,50%-55%of field maximum water holding capacity)and severe drought(D3,30%-35%of field maximum water holding capacity).The transcriptome associated with metabolomics analyzed,the molecular mechanism of color difference response of the peel of ’Lingwuchangzao’ under the interaction of elevated temperature and drought stress,the metabolic regulation patterns were explored.This study provided theoretical reference for revealing the response of formation process of fruit color to climate change in‘Lingwuchangzao’.The main results are as follows:1.Based on RNA-Seq analysis,a total of 15489 differentially expressed genes were identified in the peel of ’Lingwuchangzao’.KEGG enrichment analysis showed that the differentially expressed genes were significantly enriched in flavonoid biosynthesis metabolism and sucrose metabolism.A total of 26 differentially expressed structural genes(ZjUGAT,ZjCYP73A,ZjANS,ZjDFR,ZjCCM,ZjHCT,ZjCY75B1,ZjCHI,ZjCHS,ZjLAR and ZjCYP75A)were detected in flavonoid biosynthesis pathway.The elevated temperature treatment and drought treatment increased the expression of ZjDFR,ZjCHS,ZjANS and ZjCHI,and interaction increased the expression of ZjANS,ZjCY73A and ZjLAR.Three bHLH and two MYB transcription factors involved in anthocyanin synthesis were obtained.2.Based on LC-MS,a total of 745 differential metabolites were detected in the peel of’Lingwuchangzao’.The results of PCA and OPLS-DA analysis showed that the metabolites in peel were significantly different under different levels of air temperature and drought.KEGG enrichment results showed that the differential metabolites were significantly enriched in flavonoid biosynthesis pathway,7 key differential metabolites were mainly screened at W stage.The elevated temperature treatment and drought treatment increased the contents of pelargonidin and delphinidin.In addition,drought increased the contents of quercetin and kaempferol,and elevated temperature increased the contents of catechin,epicatechin and eriodityol.The interaction increased the contents of eriodityol,quercetin,epicatechin and kaempferol.3.According to metabolome and transcriptome analyzed,13 candidate genes for anthocyanin synthesis were highly correlated with 6 anthocyanin metabolites.The ZjCHS,ZjDFR and ZjANS genes were highly expressed in normal soil moisture(T2D1),which promoted the accumulation of the corresponding 7 metabolites in W.The high expression of genes ZjCHS,ZjCHI,and ZjANS under severe drought(T1D3)at ambient temperature further promoted the accumulation of metabolites quercetin,kaempferol,catechin,and delphinidin in C stage and the accumulation of metabolites at Z stage.The high expression of genes ZjCHI and ZjANS in severe drought(T2D3)increased the accumulation of delphintin,catechin,pelargonidin,eriodictyol and epicatechin in C and W.In conclusion,anthocyanin metabolism of peel of `Lingwuchangzao’ was significantly different under different air temperature and drought.The interaction between the elevated temperature to 2.0℃ and drought affected coloration by controlling the expression levels of key genes for anthocyanin biosynthesis ZjCHS,ZjCHI,ZjANS and ZjDFR at W,and the components and contents of anthocyanin-related metabolites.In this process,the genes of ZjCHS,ZjDFR and ZjANS were regulated by regulatory genes bHLH and MYB.