The Molecular Mechanism Of Ethylene Regulating Postharvest Ripening Of Agaricus Bisporus

Agaricus bisporus is one of the most common,most cultivated,and most edible fungi in the world.In particular,canned mushrooms are the first in international trade,which loved by people.However,harvested mushrooms have a high water content fragile and fresh tissue,and is susceptible to damage,browning,deterioration or soft rot during harvesting and storage and other ripening-related typical symptoms.The shelf life of harvested mushrooms is markedly shorter than that of other fresh fruits,which is only 3-4 days at normal temperature.A short shelf life seriously limits the sales and economic benefits of fresh mushrooms.The button mushroom produces ethylene and respiration bursts during postharvest storage as a climacteric fruit.However,the molecular mechanism for the regulation of button mushroom ripening is still unclear.Therefore,it is especially important to provide an in-depth discussion on the regulation mechanism of mature aging and provide theoretical guidance for the development of preservation technology.(1)Postharvest button mushrooms were treated with ethephon and the plant ethylene receptor inhibitor 1-methylcyclopropene(1-MCP).Then we analysis and compare sensory indicators,physical and chemical indicators of botton mushrooms.The results showed that ethylene accelerated mushroom ripening and upregulated ripening-related genes,which was in contrast to the effect of 1-MCP.(2)The expression levels of mature senescence-related genes in the postharvest Agaricus bisporus fruiting bodies were determined during storage and the 1-MCP treatment.The tyrosinase gene(PP04),the ROS gene(NoxA),the ACC oxidase(ACO)and autophagy-associated gene(Atg8)significantly upregulated expression in the mushrooms with ethephon treatment and stored for 60 h compared to the control.While both PP04 and ACO had significantly downregulated expression in the mushrooms treated with 1-MCP compared to the control.The mechanism of ethylene-regulated fruiting body mature senescence is that autocatalytic ethylene synthesis and up-regulates the expression of mature senescence-related genes,and there may be ethylene signal transduction pathway in Agaricus bisporus.(3)Effects of ethephon on the expression of postharvest mushroom ripening-related genes in button mushroom mycelia was analyzed.After ethephon treatment,the expression of Atg8,1,3-?-D-glucanase 1 gene(Exg1)PPO4 and NoxA in hyphae was significantly up-regulated,while the expression of ACO gene was not significantly up-regulated.It is indicated that ethylene can also regulate the expression of genes in hyphae,while the regulation of ACO gene is tissue-specific.(4)Using the promoter analysis software to predict the ethylene response element of the promoter region of the mature senescence-related gene in button mushrooms.It was found that there were ethylene response elements in the promoter regions of the 19 genes involved in the mature senescence of the fruiting body,among which the ACO gene promoter region has predicted three plant ethylene response elements,namely DRE/CRT,ERE and W-box.A deletion mutant containing only one plant ethylene response element in the promoter region of ACC oxidase gene ligate to the reporter gene GUS gene and then construct four transient expression vectors by using internal deletion method or 5' end deletion method.The transient expression vector was transformed into Agrobacterium tumefaciens LBA4404.The Agrobacterium tumefaciens-mediated method was used to transfer it into onion epidermal cells.The predicted three plant ethylene response elements,DRE/ERE/W-box,can be induced by ethylene in onion epidermal cells.The above results indicated that the molecular mechanism for postharvest button mushroom-ripening regulation may be similar to that of climacteric fruit.It is predicted that the ACO gene promoter region contains plant ethylene response elements and is positively regulated by exogenous ethylene.It indicates that the expression regulation of mature senescence-related genes in button mushrooms is similar to that of climacteric fruits and vegetables,autocatalytic ethylene synthesis and up-regulates the expression of mature senescence-related genes.The ethylene perception and signal transduction system in higher plants presumably exists in button mushrooms.Ethylene should be a fungal hormone.