| Peach fruit(Prunus Persica)is very popular among consumers for its sweet,juicy taste and rich nutrition.As a typical climacteric fruit,postharvest peach fruit could quickly reach to respiration and ethylene peaks at ambient temperature,and thus accelerates senescence and deterioration caused by mechanical damage and pathogenic microorganism infection.Cold storage is one of the most effective ways to retard respiration and other metabolic processes and then extend shelf life of peach fruit.However,this fruit is very sensitive to chilling injury when stored at low temperature.CI symptoms were often represented as unexpected properties like juicelessness,mealiness,leatheriness and browning.Recent reports indicated that melatonin could alleviate CI in peach fruit,while little theoretical basis was found for this effect from cell wall metabolism.Until now,the correlation between fasciclin-like arabinogalactan protein(FLA)and fruit softening remains unclear.In this study,12 putative FLA members were identified and bioinformatic analysed,and their expression in growth and developmental tissues of peach were also investigated.Meanwhile,the effect of melatonin treatment on neutral sugars composition in cell wall of peach fruit stored at low temperature was analysed to explain the mechanism of melatonin alleviation CI and discovered that FLA may participate in fruit softening under cold stress.Ultimately,the expression patterns of FLA members in postharvest peach fruit treated with exogenous ethylene and abscisic acid were also investigated to provide new insights into the molecular regulation of fruit texture during fruit ripening.Results were as follows:(1)Fasciclin-like arabinogalactan proteins(FLAs)are a subclass of a larger family of arabinogalactan proteins(AGPs)which have both AGP-like glycosylated regions and putative fasciclin(FAS)domains.12 putative FLA sequences were screened from the peach genome database.Analysis of structures of the 12 FLAs revealed that PpFLA7 seems not the classical member of FLA family due to the absence of glycosylated sites.PpFLA6 showed a significant difference with other ones because of a distinctive composition and distribution of conserved domains.Phylogenetic analysis indicated that Pp FLA family could be classified into three groups: Clade?,Clade?and Clade?.Expression analysis manifest that 12 PpFLAs were differentially expressed in various tissues during ripening of peach.These results suggest that the highest expression of PpFLA4 in firm-ripe peach fruit may play an important role in peach fruit during ripening.(2)Melatonin altered texture of peach fruit such as firmness,cohesiveness,adhesiveness,and increased extractable juice.Related to this,after melatonin treatment,loss of neutral sugars in pectin like arabinose and galactan both in CDTA-soluble and Na2CO3-soluble fraction was happened at 7 day,with their branchings,but this phenomenon were improved at 21 day.In addition,AFM analysis manifested that polysaccharides width of cell wall in treated fruit were mainly distributed in a shorter range which indicated more serious degradation of pectin.FLA family gene members showed a uniform up-regulated expression pattern by melatonin,suggesting that they were probably involved in response to melatonin induced fruit softening and functioned in protecting cell wall from abnormal rapid disassembly.(3)Exogenous ethylene and ABA could enhanced the expression of FLA members including PpFLA2,PpFLA4,PpFLA5,PpFLA6,PpFLA8 in peach fruit stored at normal temperature,which suggested that certain FLAs maybe involved in ethylene or ABA signal pathway regulation and related to fruit softening.Exogenous ethylene and ABA also promoted significantly higher expression levels of PpFLA4 and PpFLA6.These results indicated that FLA members may be involved in fruit cell wall metabolism,and inhibit the breakdown of flesh tissue which hydrolyzed by cytohydrolist. |
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