Study On The Response Mechanism Of The Gamma-aminobutyrate Shunt To The Resistance Of Peach Fruit Towards Brown Rot Induced By Nitric Oxide

Peach fruit is one of the most popular commercial fruits in China.However,the hot and rainy environment and the exuberance of its own respiratory metabolism during harvest period make it susceptible to pathogens.Once infected,peach fruit will quickly decay and infect other fruits,causing serious postharvest losses.Brown rot is one of the main susceptible diseases for postharvest peach fruit,and Monilinia fructicola is the dominant strain triggering such disease,which wreaks havoc throughout the country.At present,there are prevention measures to control such disease,but they have many disadvantages,such as threatening human health,causing adverse effects on fruit and difficulty in application for postharvest industry.Currently,plant disease resistance inducers have shown great application potential in controlling postharvest diseases of fruit and vegetables.Nitric oxide(NO)and γ-aminobutyrate(GABA)that can induce disease resistance have been confirmed in numerous studies on postharvest diseases of fruit and vegetables.NO can induce plant disease resistance through signal transduction,and GABA is able to resist different pathogens via the different reaction modes of the GABA shunt.However,the effect of the GABA shunt in NO-induced plant disease resistance is not clear.Therefore,in this study,‘Qingzhoumi’ peach fruit,as experimental material,were treated with a NO donor nitrosoglutathione(GSNO)and NO scavenger(2-(4-carboxyphenyl)-4,4,5,5-tetramethylimidazoline-1-oxyl-3-oxide,c PTIO)to explore the mechanism of the GABA shunt in NO-induced peach fruit resistance to brown rot,as well as the contribution of related pathways to the mechanism of the GABA shunt.The main research results are as follows:(1)NO treatment significantly reduced the disease incidence and lesion diameter of peach fruit inoculated with M.fructicola,increased the endogenous NO content in peach fruit,while the endogenous NO level of peach fruit treated with NO scavenger c PTIO decreased,and the disease of fruit became worse,which indicated that NO and c PTIO treatment could affect the disease condition of peach fruit inoculated with M.fructicola by regulating endogenous NO content.(2)NO treatment enhanced the activity and gene expression of glutamate decarboxylase(GAD),γ-aminobutyrate transaminase(GABA-T),succinic semialdehyde dehydrogenase(SSADH),diamine oxidase(DAO)and polyamine oxidase(PAO),as well as the transcriptional activity of betaine aldehyde dehydrogenase(BADH),fully activating the synthesis and metabolism of GABA.However,the GABA shunt and polyamine degradation pathway were both inhibited by c PTIO treatment.Therefore,the content of glutamate,GABA and polyamine in NO-treated group was significantly lower than that in c PTIO-treated group.(3)Nitrosoproteomic analysis showed that Cys-72 of GAD4,Cys-235 and Cys-461 of GABA-T3 as well as Cys-488 of SSADH were all nitrosylated.At 6 h and 12 h,NO treatment up-regulated the nitrosylated level of GAD4,GABA-T3 and SSADH,which may be related to the activation of the GABA shunt.(4)NO treatment enhanced the activity and gene expression of succinate dehydrogenase(SDH),as well as the prophase gene expression of malate dehydrogenase(MDH)and α-ketoglutarate dehydrogenase(α-KGDH)in the tricarboxylic acid cycle.Accordingly,the content of ATP and the level of energy charge in NO-treated fruit were elevated.Nevertheless,c PTIO treatment played the opposite role.The contents of adenosine diphosphate(ADP)and adenosine monophosphate(AMP)in the three treatments were in reverse order,which may contribute to the stability of the energy system.(5)NO treatment up-regulated the expression level of nonexpresser of pathogenesisrelated genes 1(NPR1),TGACG motif-binding factor 1(TGA1)and pathogenesis-related protein 1(PR1)in salicylic acid(SA)signal pathway,and enhanced the activity and gene expression of chitinase(CHI)and β-1,3-glucanase(GNS),thus improving the defense level of peach fruit,but c PTIO treatment hindered the construction of such defense.(6)The expression of Pp GLR3.3,Pp GLR3.4,Pp GLR3.6 and Pp GLR3.7 in glutamate receptor(GLR)family,together with Pp ALMT4 and Pp ALMT9 in aluminum-activated malate transporter(ALMT)family,as well as the gene expression of glutamate dehydrogenase(GDH)were all induced by NO treatment,which was completely contrary to the effect of c PTIO treatment.Among them,GLR and ALMT may participate in signal transduction as the receptor of glutamate and GABA respectively;GDH can effectively promote the response of the GABA shunt.