| During the storage and transportation of postharvest persimmon,ethylene can induce the softening of the fruits.It is of great significance to control ethylene biosynthesis to prolong fruit shelf life.At present,there is no report on the initiation mechanism of ethylene biosynthesis in persimmon fruits.This study takes "Gongcheng Perimmon",a characteristic variety of Guangxi Province as experimental material to study the relationship between oxidation-reduction potential and initiation of ethylene biosynthesis.At the same time,the group of fruits after ethphon treatment and the control group were subjected to comparative transcriptome sequencing.Through bioinformatics analysis,genes related to the initiation of ethylene biosynthesis were initially screened out and relevant candidate genes were identified by real-time qRT-PCR.The expression verification was conducted to investigate the initiation mechanism of ethylene biosynthesis and provide a theoretical basis for establishing a biological model for the initiation of ethylene synthesis.The results show that:1.The initiation of ethylene synthesis of postharvest persimmon is closelyrelated to oxidation-reduction potential and antioxidants.It was found that the ORP of the ethephon treatment group on the 1st day of storage decreased rapidly from 8.29 mV·g-1 to 5.44 mV·g-1,while the ethylene biosynthesis amount increased rapidly from 0.028 ?L·kg-1·h-1 to 0.529?L·kg-1·h-1.On the 2nd day of storage,the hardness of the fruit rapidly decreased,and the total color difference rose rapidly.During the whole storage period,the ORP of the control group was relatively stable,and the ORP of the ethephon treatment group first decreased and then increased.The ethylene biosynthesis of the fruit was maintained at a high level of 0.576?L·kg-1·h-1 during the storage period,which was much higher than that of the control group.During the post-harvest period,the activities of antioxidant enzymes such as SOD,POD,GR,and APX were significantly positively correlated with ethylene biosynthesis.The antioxidants like flavonoids,total phenols,anthocyanins,glutathione,and ascorbic acid were consumed significantly so that the content was lower than the control group,and the total phenol content was significantly negatively correlated with the amount of ethylene biosynthesis.This indicated that the initiation of ethylene synthesis of postharvest persimmon is closely related to the steady state of ORP.The antioxidants(flavonoids,total phenols,anthocyanins),antioxidant enzymes(SOD,POD),and AsA-GSH circulatory system regulate the ORP status of the fruit through synergistic effect.The stimulation of exogenous ethephon leads to imbalance of ORP in fruit to initiate ethylene biosynthesis,which in turn promotes fruit ripening and softening.2.Excavation and analysis of ethylene-related genes in persimmon fruits.A comparative transcriptome sequencing was performed on the fruit materials of ethephon treatment(DK_ETH1)and control(DK_CK0,DK_CK1).A total of 28.49 G transcripts were obtained and138177 Unigenes were annotated after transcript assembly.Through the comparative analysis of differential expression in three transcriptome libraries,a total of 1082 DEGs were obtained,of which DK_ETH1 vs DK CK1 had the most DEGs screened(929).Pathway significant enrichment analysis of DEGs between ethephon treatment and control samples showed that in the DK_ETH1 vs DK_CK0 and DK_ETH1 vs DK_CK1 alignment groups,the most enriched was plant hormone signal transduction pathways.19 and 27 Unigene were enriched to up-regulated expression respectively,followed by cysteine and methionine metabolism,which was 14 and 16 Uni gene respectively.At the same time,it was also enriched to up-regulated expression in some of the antioxidant anabolic pathways related to carotenoid biosynthesis,glutathione metabolism,nicotinic acid,nicotinamide metabolism,and other antioxidant pathways.This shows that a large number of genes are involved in the initiation of ethylene synthesis in persimmon fruits,and the synthesis and metabolism of antioxidants are closely related to the initiation of ethylene synthesis.3.Verification of the expression of genes involved in the initiation of ethylene synthesis during storage of postharvest persimmon fruits.The key enzyme gene metE for the synthesis of two methionines in the ethephon treatment group on the 1st day of storage increased dramatically from the initial 0.915 and 0.708 to 17.85 and 23.8 respectively,far more than that of the control group and the later stage of ethephon treatment group.During the storage period,the expression pattern of F-box protein gene EBF1 and respiratory burst oxidase gene RBOH in the ethylene signal transduction pathway was similar to that of gene metE.Among the three cytochrome P450 genes,the expression level of CYP72A219 in the ethephon treatment group was significantly higher than that in the control group.This indicated that exogenous ethylene activated RBOH gene and CYP72A219 gene,which promoted the generation of reactive oxygen species ROS to break the redox balance in the fruit,and activated gene metE at the same time so that methionine was accumulated rapidly in the fruit,and then the ethylene biosynthesis was initiated.The ethylene receptor ETR regulates the onset of fruit ripening by enhancing the ethylene perception during the initiation of ethylene synthesis.Simultaneously,The gene EBF1 was shown to be insensitive to ethylene by overexpression when it was activated in ethylene to resist the external stimulation to promote fruit ripening.In summary,the hypothesis is that the initiation mechanism of ethylene biosynthesis is as follows:When exogenous ethylene stimulates persimmon fruits,the oxidation and reduction systems in the fruit cells are out of balance,and the ORP balance of the body is broken.Once the ORP equilibrium is broken,it will lead to stress reaction in the fruit,and activate the metE gene at the same time,which will rapidly accumulate methionine to activate the ethylene synthesis pathway,initiate ethylene biosynthesis,activate the ethylene receptor ETR and accelerate fruit maturation and senescence. |
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