Preliminary Study On The Mechanism Of Postharvest Plum (Prunus Salicina L. Kongxinli) Fruit Reddening Based On Transcriptomics And Metabolomics

The plum fruit(Prunus salicina L.Kongxinli),which is named after the natural separation of flesh and stone during the mature period,is a characteristic famous plum in Guizhou Province.The quality and commodity value of the fruit decreased during peel reddening at room temperature storage,which will affect the quality and commodity value of the fruit seriously.However,the mechanism of fruit reddening of plum fruit is still unclear.In the current study,plum fruit stored at room temperature was employed as the experimental material,the quality and physiological indicators of the plum fruit were detected during reddening,and a preliminary analysis of the mechanism of fruit reddening was demonstrated by means of the combined analysis of metabolomics and transcriptomics.Moreover,the corresponding results were validated using ultra performance liquid chromatography and tandem mass spectrometry(UPLC-MS/MS)and qRT-PCR technology.This study is of great significance in exploring the mechanism of fruit reddening,formulating corresponding regulatory measures to extend the storage and shelf life of fruits,and reducing the occurrence of fruit reddening.The main research results were as follows:1.The plum fruit exhibited obvious reddening,which occurred on the fifth day of storage at room temperature,and the redness became worse after 10 days.The quality and physiological indexes of plum fruits at green fruit stage(GF),half red fruit stage(HR)and full red fruit stage(RF)were compared.The results demonstrated that fruit brightness(L*),color saturation(C*),firmness,superoxide dismutase(SOD)activity at GF were dramatically higher than those at HR and RF stages,while a*value,solid acid ratio(TSS/TA),malondialdehyde content(MDA),total phenols content,total flavonoids content,total anthocyanin content,peroxidase activity(POD),catalase activity(CAT)were markedly higher than that of GF and HR fruits.There were apparent differences in fruit quality among the three periods,and the fruit quality and commodity value in RF period manifested the lowest.2.UPLC-MS/MS was chosen to conduct extensive targeted metabolomic analysis of the pericarp of plum fruit at GF,HR and RF.A total of 495 secondary metabolites were detected,and 184 differential tabolites were screened.The differential metabolism included four anthocyanins,namely cyanidin-3-O-rutinoside,cyanidin-3-O-arabinoside,peonidin-3-O-glucoside,and cyanidin-3-O-glucoside.The metabolic pathway was mainly concentrated in phenylpropane biosynthesis,flavonoid biosynthesis and anthocyanin biosynthesis.Therefore,the redness of the plum fruit was primarily due to the accumulation of anthocyanins,and the dominating components of anthocyanins were cyanidin-3-O-glucoside,cyanidin-3-O-rutoside,cyanidin-3-O-arabinoside,and peonidin-3-O-glucoside.3.A total of 3786 differentially expressed genes(DEGs)were identified by transcriptome sequencing in the pericarp of plum fruit at GF,HR and RF stages,including 20 DEGs related to anthocyanin synthesis,which were PAL1,C4 H,CHS1,CHS2,CHI1,CHI2,CHS3,DFR2,ANS1,and UFGT2 were positively correlated with anthocyanin content.In addition,there were 251 TFs in the DEGs,of which 6 MYBs,7WRKYs,and 1 bHLH were notably associated with anthocyanins.Therefore,these genes might play an important role in the reddening process of plum fruit.4.The absolute quantitative analysis of anthocyanin was carried out on the reddening fruit of plum in three periods,which further confirmed that the red change of plum fruit was due to the accumulation of cyanidin-3-O-glucoside and cyanidin-3-O-rutoside,and the contents of cyanidin-3-O-glucoside and cyanidin-3-O-rutin were 89% of the total anthocyanidins in RF period.Therefore,these two anthocyanins were the main components of plum fruit during reddening.5.Four structural genes PAL1,C4 H,CHS1,DFR2,as well as three transcription factors MYB75,bHLH62,and WRKY71 were demonstrated to be remarkably positively correlated with monomeric anthocyanins.Therefore,these 5 DEGs and 3TFs were key genes involved in the process of plum fruit during reddening.In summary,the study indicated that the main reason for the skin redness of postharvest plum fruit during room temperature storage was the accumulation of cyanidin-3-O-glucoside and cyanidin-3-O-rutoside.PAL1,C4 H,CHS1,and DFR2 were the key structural genes related to the reddening of plum fruits,which could promote skin coloring by positively regulating pericarp reddening.And drastical correlations were confirmed between MYB75,bHLH62,and WRKY71 transcription factors and anthocyanin synthesis.