The Regulation And Mechanism Of Low Temperature And Peach-Gum Coating On Postharvest Peach Ripening And Senescence

Cold storage is extensively used to extend the shelf-life of peach fruit.Nevertheless,the molecular mechanisms underlying its impact on postharvest fruit ripening and senescence remain less well understood.In this study,integrated transcriptome and metabolome studies were performed on cold-stored fruit from two peach varieties(‘Tian Xian Hong' and ‘Jin Xiu'),with the aim of gaining deeper insight into the physiological and molecular response of peach fruit to long cold storage.Edible coating is not only safe,nutritious and environmentally friendly,but also can reduce the loss of moisture of stored fruit,delay ripening and senescence,and improve the antibacterial property of peel,making it a popular fruit preservation technology.In order to explore the potential of peach gum as edible film substrate in delaying fruit ripening and softening after harvest,we studied the effect of peach gum film on the storage performance and transcriptional surface of peach fruit in low temperature storage.The gene with ID of Prupe.1G220700 was significantly up-regulated during the cold storage of the two cultivars,while the expression was down-regulated after peach-gum treatment.It is a SWEET(Will Eventually be Exported Transporters)gene,which has the highest homology(59.84%)with the At SWEET15 gene,and we name it Pp SWEET15.It was speculated that this gene plays an important role in cold storage of peach.Therefore,bioinformatics and expression analysis were conducted on the Pp SWEETs gene family,and the gene was transformed into yeast and micro-Tom tomato for preliminary exploration of its function.The main results are as followed:(1)Dynamic changes of transcriptome and metabolome in cold stored peach.A total of 344 common genes were detected to be differentially expressed during the early storage stage(S2/S1)of both genotypes.In this stage,pathways related to primary metabolism exhibited prominent variation.Pathways that generate glucose and fructose,including the decomposition of starch,glycan and sucrose,showed elevated expression to meet energy needs.However,pathways involved in glucose and fructose consumption such as glycolysis,pyruvate metabolism and fructose metabolism were downregulated.In the later stage(S3/S2),only 41 common differentially expressed genes were identified.Primary metabolism remained steady.Sucrose and sorbitol together acted as the main energy sources.Meanwhile,phenylpropanoid and flavonoid biosynthesis,representing secondary metabolism were promoted,suggesting the needs for antioxidant substances to resist senescence and cold stress.Some amino acids and organic acids that have been reported to be involved in stress defense,including proline,serine,?-aminobutyric acid(GABA)and succinate,accumulated during the storage.The S2/S1 and S3/S2 stage of long cold storage could be termed as the quality maintenance period and the quality deterioration/stress responses period respectively.Energy supply and stress defense may be major areas of future research in postharvest peaches.(2)Peach-gum can be used as a new edible coating material to preserve peach fruit.Compared to control(CK),treatment with all tested concentrations(1%,5%,and 10%,v/v)of peach-gum repressed ethylene production and fruit softening,and to some extent,prevented weight loss.Peach-gum treatment did not alter malic acid,citric acid,quinic acid,glucose,fructose,or sucrose content,but it repressed the reduction in sorbitol.The expression of numerous genes related to fruit softening and cell wall degradation were repressed by peach-gum treatment,in accordance with the delayed softening observed.Meanwhile,the expression of senescence-associated genes,chitinase genes,and pathogenesis-related genes that were up-regulated during cold storage,were also inhibited by peach-gum treatment.21 zinc finger proteins from the four TF families,C2H2,C3 H,CO,and Dof,which have been reported to be widely involved in plant growth and development,were up-regulated in peach-gum-treated fruit.We hypothesize that these transcription factors may play a negative regulatory role in peach maturation and senescence.Among the genes differentially expressed between peach-gum-treated and control fruit,genes involved in indole-3-acetic acid(IAA)transport and auxin response were relatively statistically overrepresented.The content of IAA in peach gum treated fruit was significantly lower than that in control,suggesting that IAA plays an important role in the maturation and senescence of peach fruit.As one of the hormones most closely related to fruit ripening and senescence,the content of abscisic acid is markedly lower in peach-gum-treated fruit than in control fruit,indicating that peach gum treatment may inhibit the ripening and senescence of peach fruit.(3)Expression characteristics and functional analysis of the candidate gene Pp SWEET15 related to ripening and senescence of peach fruit.The gene with ID of Prupe.1G220700 was significantly up-regulated during the cold storage of the two cultivars,while the expression was down-regulated after peach-gum treatment,suggesting that this gene may be involved in the ripening and senescence of peach fruit.Further analysis revealed that,Prupe.1G220700 is a SWEET(Sugars Will Eventually be Exported Transporters)gene,which has the highest homology with the At SWEET15 gene,and we name it Pp SWEET15.Gene expression analysis revealed that Pp SWEET15 is highly expressed in stems,senescent leaves and mature fruits and is induced by low temperature,suggesting that Pp SWEET15 may be mainly involved in fruit ripening,senescence and stress response.The transformed yeast strain of p PMA1-Pp SWEET15-EBY.VW4000 could not grow normally on the medium of sucrose,glucose,fructose,galactose and sorbitol,suggesting that Pp SWEET15 does not have the transport capacity of these sugars.The fruits of T0 generation transgenic plants overexpressed Pp WEET15 gene appeared early flowering and fruit-bearing,the fruit tips disappeared,and the seedless rate was high.The content of fructose and glucose in fruits of T0 generation was lower than control plants.The phenotype of transgenic plants overexpressed Pp WEET15 gene and the function of Pp WEET15 in postharvest fruit ripening and senescence need to be further identified.