Preliminary Study On The Molecular Mechanism Of Ethylene Production System I And II Transformation In 'Hongyang' Kiwifruit After Harvest

Kiwifruit is rich in nutrition and is loved by consumers.However,because kiwifruit is a climacteric fruit,it is easy to soften and rot during the postharvest storage period,and the Postharvest loss is as high as 30%,which seriously affects the consumer desire for consumption.Ethylene is the key signal molecule of kiwifruit ripening and softening after harvest.ACC synthase(ACS)and ACC oxidase(ACO)are important rate limiting enzymes in the process of ethylene production.The ethylene biosynthesis during kiwifruit ripening and senescence is regulated by systems ? and ?.Most of the physiological and biochemical changes related to fruit maturation,such as starch hydrolysis,color changes and fruit softening,occur in the system phase ? that does not produce significant ethylene.Further softening and maturity,the production of volatile substances aroma occurs in the phase ? of the ethylene production system.The transition of kiwifruit ethylene system from phase I to phase ? is a potential regulatory target for prolonging the edible shelf life of kiwifruit.The current research on the regulation of ethylene in kiwifruit mainly focuses on signal transduction pathways and related key gene expression regulation.There are few reports on the molecular mechanism of the transformation of ethylene production system ? to ?.This article takes 'Hongyang' kiwifruit as the research object to study the difference in the activities of the key enzymes ACS and ACO for ethylene production after fruit harvest,qRT-PCR is used to study the difference in gene expression changes of the key enzymes ACS and ACO that affect ethylene production.Cloning of the key genes for the transition from ethylene production system ? to ?,and clarify the molecular mechanism of the transformation of kiwi ethylene production system ? to ?,in order to provide new ideas and theories for the study of kiwi ethylene production mechanism after harvest and delay fruit senescence foundation,to provide support for the development of storage and fresh-keeping technology to extend the edible shelf life of kiwifruit.The main results and conclusions are as follows:(1)The changes of ACS and ACO activities in 'Hongyang' Kiwifruit during postharvest storage were related to fruit ripening:the hardness continued to decrease,the soluble solid content increased,breathing jumps and ethylene release peak rate occurred when stored at room temperature 20?.The peak of ethylene release rate appeared before the breathing jumps.While the peak respiratory rate and the breathing jumps occurring simultaneously were discovered in the fruit treated by ethylene.The change trend of ACS and ACO activity is consistent with the change of ethylene release rate,and ACS and ACO are related to the production of ethylene.Ethylene treatment can accelerate the arrival of kiwifruit respiration peak,ethylene release rate peak and the peak of ACS and ACO activity changes.Exogenous ethylene has a certain induction effect on fruit respiration,ethylene production,ACS and ACO.(2)The expression differences of ACS and ACO gene family members during postharvest storage of 'Hongyang' kiwifruit were as follows:When stored at room temperature at 20?,the expression of AcACS1?6 genes in the ACS gene family of the control group increased sharply on the 11th day,which was 1-2 times that of the 9th day.The ACS gene expression in the ethylene treatment group was compared with the control group was no significant difference on the 1-7th day.The expression of AcACS1 and AcACS3-6 genes in the treatment group on the 9-11th day was lower than that of the control group.AcACO1 and AcACO3 in the ACO gene family are positively regulated by ethylene during the storage period of kiwifruit,while AcACO2 is regulated by the inhibition of ethylene.Exogenous ethylene can inhibit the expression of AcACO2.AcACO1 and AcACO3 in the ACO gene family are consistent in expression and enzyme activity changes with ethylene production.It is speculated that the genes AcACO1 and AcACO3 are the key genes for the transition from ethylene production system I to system II.(3)The cDNA cloning of ACO gene family members from 'Hongyang' kiwifruit:six ACO genes were successfully cloned from the 'Hongyang' kiwifruit,followed by AcACO1?6.The sequence of coding region of AcACO1?6 is 1101?1270bp,which encodes 352?402 amino acids.AcACO1?6 have a conserved domain PLN02299,which has ACO enzyme catalytic activity.AcACO1?6 have no transmembrane domain and are non-secreted proteins.AcACO1?6 protein secondary structure is composed of ?-helix,?-turn and extended chain.The main components of AcACO1 and AcACO5 proteins are ?-helices,and the main components of AcACO2,AcACO3,AcACO4,and AcACO6 proteins are random coils.According to homology comparison and evolutionary tree analysis,the nucleotide sequence homology of the six kiwifruit ACO genes is 28.3%-99.3%,and the six genes are clustered into two categories.The homology of nucleotide sequences of the same kind is more than 70%,and the homology of nucleotides between groups is only about 40%.AcACO1 has high homology with VvACO1 of grape.