| Suberization is an important phenomenon of wounded fruit,and the suberin acts as a lipidphenolic cell wall barrier that prevents water loss and pathogen infection in the wounded plant.Suberin polyphenolic(SPP)monomers are the main components of suberin,which are polymerized from monomers produced by the phenylpropane metabolic pathway after a series of enzyme-catalyzed reactions.At present,there are many reports on wound suberization in model plants Arabidopsis and potato,and few reports about mechanical damage focus on the process of fruit harvesting,transportation,processing,and marketing.Besides,most studies focus on the regulation of wound suberization by a single hormone,but the effect of multi hormone interaction on wound suberization has not been revealed.In this study,kiwifruit(Actinidia chinensis Planch.Cv.Xuxiang)was used as experimental material to preliminarily explore and discover the two stages of the wound healing process and the change characteristics of various hormones,the promotion of methyl jasmonate(Me JA)on the wound healing of kiwifruit by activating the metabolism of phenylpropane and further exploring the molecular mechanism of the interaction of abscisic acid(ABA)and jasmonic acid(JA)in regulating the formation of SPP in kiwifruit.(1)ABA may stimulate the wound suberization of kiwifruit by coordinating with JA,trans zeatin(t-ZT),and indole-3-acetic acid(IAA).In the early stage of wound healing(within 24 h),ABA content rapidly increased and induced the jasmonic acid(JA)biosynthesis.ABA level gradually decreased with the expression of Ach CYP707 A genes,while the contents of transzeatin(t-ZT)and indole-3-acetic acid(IAA)steadily increased at the late stage of wound healing(after 24 h).Meanwhile,long-chain fatty acids,long-chain ω-hydroxy fatty acids,and SPP monomers in kiwifruit wound tissues slowly accumulated at the early stage,while 2-hydroxy fatty acids,glycerides,and SPP monomers in kiwifruit wound tissues were produced in large quantities.In addition,exogenous ABA stimulated JA and suberin monomers accumulation but suppressed both t-ZT and IAA biosynthesis.Thus,the wound healing process of kiwifruit is regulated by multiple hormones,and ABA and JA play a predominant role in regulating the wound suberization of kiwifruit.(2)Wound healing in kiwifruit could be promoted by Me JA via activation of phenylpropanoid metabolism.Methyl jasmonate(Me JA)treatment leads to increases in endogenous JA biosynthesis,lipoxygenase(LOX)and 12-oxo-phytodienoic acid reductase(OPR)activities,and JA synthesis genes expression,while DIECA(JA biosynthesis inhibitor)represses these processes.Meanwhile,Me JA promoted the autofluorescence of suberin polyphenolic(SPP)and the accumulation of SPP monomers.The Me JA-treated group demonstrated significantly enhanced total phenols,flavonoids,and lignin contents.Besides,Me JA promoted the activities of phenylalanine ammonia-lyase(PAL),cinnamic acid-4-hydroxylase(C4H),4-COumaric-COA ligase(4CL),peroxidase(POD),polyphenol oxidase(PPO),and the respective gene expression levels.(3)Me JA induced transcription factor Ach MYC2 regulates SPP formation in kiwifruit wound tissues.Three general phenylpropanoid metabolism-related genes,Ach PAL,Ach C4 H,and Ach4 CL,respectively encoding phenylalanine ammonia-lyase(PAL),cinnamic acid-4-hydroxylase(C4H),and 4-coumaric-Co A ligase was determined in tobacco(Nicotiana benthamiana)leaves overexpressing these genes.Besides,the positive regulation of Ach MYC2 on Ach PAL,Ach C4 H,and Ach4 CL was observed.JA-induced Ach MYC2 locating in the nucleus activated the transcriptional expression of Ach PAL,Ach C4 H,and Ach4 CL through binding to their promoters.The results were further evidenced in the overexpressing of Ach MYC2 tobacco leaves in which Ach MYC2 enhanced the expression levels of Nb PAL2,Nb C4 H,and Nb4CL1 and enhanced the accumulation of the phenolic acids including cinnamic acid,p-coumaric acid,caffeic acid,ferulic acid,and sinapic acid.Meanwhile,the contents of phenolic acids in the kiwifruit wound tissues were increased by Me JA,but reduced by DIECA.Together results indicated that Ach MYC2 activated Ach PAL,Ach C4 H,and Ach4 CL transcription to promote JA-mediated suberin polyphenolic accumulation in the wound healing of kiwifruit.(4)The interaction between ABA and JA in the regulation of SPP synthesis in kiwifruit wound tissues.Blocking JA biosynthesis significantly reduced the positive effect of ABA on the accumulation of SPP.Besides,transiently overexpressed the Ach LOX3 and Ach OPR3 in tobacco(Nicotiana benthamiana)leaves confirmed that these two genes respectively encoded lipoxygenase and 12-oxo-phytodienoic acid reductase involved in JA biosynthesis.ABAinduced Ach ABF-1 located in the nucleus activated the transcriptional expression of Ach LOX3 and Ach OPR3 through binding to their promoters.These results were further confirmed in the tobacco leaves overexpressing Ach ABF1-1 in which Ach ABF1-1 promoted Nb LOX and Nb OPR expression with the increases of JA content.In addition,exogenous ABA increased endogenous JA content,and enhanced LOX and OPR activities as well as their related gene expression in the kiwifruit wound tissues,while FLD reduced these indices.These results suggested that wounding induced ABA signaling to activate JA synthesis through the transcription factor Ach ABF1-1,and further promoted SPP synthesis... |
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