| Cassava（Manihot esculenta Crantz）is a plant in the Euphorbiaceae family,which is an important food crops used for staple,biofuel and feedstuff in the world.It is called one of the three largest potato crops in the world with potato and sweet potato.After cassava harvest,the tuberous root is not tolerant to storage in room temperature.Cassava tuberous roots will be decay after havesting for 1 to 3 days,and brown or green brown occurs in the surrounding parts,called as postharvest physiological deterioration（PPD）.PPD seriously damages the economic benefits of farmers and processing enterprises,which is an important problem to be dealt with in the development of cassava industrialization.In the present study,the tuberous roots of cassava SC9 with different degrees of PPD are used as materials,and LC-MS techniques and multivariate statistics are used to screen differential metabolites and metabolic pathways of cassava tuberous roots with different degrees of PPD.The multivariate statistical analysis,univariate analysis,volcano map,KEGG annotation,metabolic pathways and other non-targeted metabolomics analyses were carried on in the present study.The aim is to explore the metabolism of cassava tubersou root after harvesting,to dig out the key metabolites and metabolic pathways that affect root PPD,providing a new clue for breeding cassava new varieties to be resistant to PPD after harvesting.The main findings are as follows:（1）According to scanning electron microscopy observations of cassava tuberous roots at 0,3,6,9,and 12 days in root temperature after harvesting,the cassava tuberous roots were intact at 0 and 3 days,and the small starch granules accumulated into a rosary shape,starting from the 6th day.With the deepening of cassava rot,the thin-walled cells of cassava appear dehydrated and shrunk,the amyloid coating was degraded and disappeared,the starch granules with irregular shapes weere released,and the starch granules were scattered,showing angularity.（2）There are 11 marker metabolites involved in PPD changes of cassava tuberous roots after harvesting:9（S）-HODE,12-OPDA,9（S）-HpOTrE,Scopoletin,Orotidine,Epicatechin,N1-（5-Phospho-a-D-ribosyl）-5,6-dimethy lbenzimidazole,Pantetheine,Glutathione,S-Lactoylglutathione,7-Aminomethyl-7-carbaguanine.Epicatechin and Scopoletin were the most remarkable.（3）Eleven mark metabolites in main enrichment on metabolic pathways included glutathione metabolic pathways,alpha linolenic acid metabolic pathways,pyruvate metabolism pathway,benzene propane biosynthesis pathway,flavonoids biosynthesis pathway,linoleic acid metabolic pathways,porphyrin and chlorophyll metabolic pathways,porphyrin and chlorophyll metabolism pathways,pyrimidine metabolic pathways,phenylalanine metabolic pathways,folic acid biosynthesis pathway.（4）The absolute contents of the key metabolites were determined by high performance liquid chromatography（HPLC）.The concentrations of（-）-Epigallocatechin and L-Epicatechin increased significantly with the change of PPD degree,and the concentration of L-Epicatechin increased significantly.Cyanidin-3-o-glucoside concentration first decreased and then increased significantly,and the results were consistent with the metabolomics data.（5）Eight key genes were selected from the flavonoid metabolism pathway where PPD key metabolite Epicatchin,including Anthocyanidin reeducate（ANR）、Leucoanthocyanidin reductase（LAR）、Leucoanthocyanidin reductase-like（LARI）、Dihydroflavanol reductase（DFR）、Anthocyandin synthase（ANS）、Putative dihydroflavonol 4-reductase（PDFR）、Bifunctional dihydroflavonol 4-reductase（BDFR）、Flavanone 3-hydroxylase-like（F3H）.The gene expression levels were used to validate for the differential metabolites.The qRT-PCR results showed that the expression of ANR,LAR,LAR1,DFR,ANS upregulated following PPD changes.The expression of PDFR upregulated slightly.However,the expression of BDFR and F3H downregulated with the changes of PPD.The gene expressions were consistent with the results from non-targeted metabolomics analyses. |
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