Expression Characteristics And Function Of Peach PG(polygalacturonase) Family Members During Fruit Ripening And Softening

Polygalacturonase is an important pectinase and involves in many process of plant growth and develepment through degraded pectin of primary wall and middle lamella.Many studies indicted that PG palys an important role in ripening and softening of peach fruit.However,the research of PG gene family and PG gene function were limited in peach.To understand mechanism of PG regulated softening and texture changes in peach fruit,PG family members are identified based on peach genome.Expression characteristics of PG family members are also analysed using fast-softening ‘Qian Jian Bai'(QJB),slow-softening‘Qin Wang'(QW),hard-melting ‘Sha Hong'(SH)and non-melting ‘Jin Tong 5 Hao'(JT5)during different tapy peach ripening and softening.In addition,the function of PpPG21 and PpPG22 is confirmed by Virus Induced Gene Silencing(VIGS)in ‘Chi Yue'(CY)peach fruit.The results are as follows:1.45 PG family members are identified and named as PpPG1-45.They have at least two of PG gene typical four conserved domain.45 PpPGs are were clustered into six subclasses,contained 4-6 exons and 3-8 introns and gene structure is basically conserved in each subclass except for subclasses E.In addition,45 PpPGs are distributed on all peach chromosomes.2.16 PpPGs are expressed in ripening and softening of peach fruit according to transcriptome results.The eight PpPGs(PpPG1,-10,-12,-13,-15,-23,-21,and-22)in QJB and three PpPGs(PpPG15,-21,and-22)in QW exhibited softening-associated patterns,which also were affected by ethylene treatment.It indicated that more PGs play a role in fast-softening peach varieties,and fewer in slow-softening peach fruit.The six PpPGs(PpPG1,-10,-12,-11,-14,and-35)are lower levels,in QW,but their expression rapidly induced by ethylene.These PpPGs may participate in peach fruit softening.While PpPG24,-25,-38 are expressed lowly and not induced by ethylene,PpPG6,-39 are not expressed.So these PpPG genes may not be involved in softening of peach fruit.3.The ten PpPGs(PpPG1,-10,-11,-12,-13,-15,-21,-22,-23,-25)are up-regulated and may be involved in SH softening.In addition,the six PpPGs may not be correlated with SH softening,including PpPG24,-35,-38(expressed steadily),PpPG14(down-regulated)and PpPG6,-39(no expression).In JT5,two PpPGs(PpPG1,-10)are up-regulated and may be involved in JT5 softening.The three PpPGs(PpPG12,-23,-25)are increased first and then decreased and may be slightly involved in JT5 softening.The eleven PpPGs may not be involved in JT5 softening,including PpPG35,-24,-11,-38,-13(expressed steadily),PpPG14(down-regulated),PpPG6,-15,-21,-22,-39(no expression).What is more,the results indicated that the six PpPGs(PpPGs1,10,11,15,21,22,25)are correlated with fruit texture changes and the eight PpPGs(12,13,14,23,24,35,38,39)are not correlated with fruit texture changes in peach.4.CY fruit firmness is increased significantly and ethylence production is reduced markedly when PpPG21 and PpPG22 are down-regulated.PpPG21 is decrased significantly at 4-10 DAH and PpPG22 is declined rapidly at 4,6,10 DAH in down-regulation PpPG21 and PpPG22 fruit.In addition,down-regulation of PpPG21 and PpPG22 lead to delay cell wall degradation,reduce PG enzymatic activity at 6-10 DAH and improve cell integrity.WSP and CSP content are decrased but ISP content are higher in RNAi fruit.TPA experiment indicates down-regulation of PpPG21,22 have a large impact on Adhesiveness,followed by Cohesiveness,Gumminess and Resilience,finished with Chewiness and Springiness.