Exogenous γ-Aminobutyric Acid (GABA) Treatment Suppresses Ethylene Biosynthesis in Hardy Kiwifruit (Actinidia aruguta) During Postharvest Storage

γ-Aminobutyric acid (GABA) plays an important role in plant development and postharvest properties of fruits. However, studies on regulation of kiwifruit ripening by GABA are scarce. Here, we evaluted physicochemical characters and the expression profile of genes related to ripening in hardy kiwifruit treated with exogenous GABA compared to control during postharvest storage period. The results showed that (1) exogenous GABA treatment not only improved the fruit quality but also inhibited respiration rate and ethylene production, as well as reduced the enzyme activities of ACC oxidase (ACO) and ACC synthase (ACS), via down-regulating the expression of AaACO1 and AaACO3, AaACS1 and AaACS2 during kiwifruit storage period; (2) on the one hand, overexpression of AaGAD1 or AaGAD4 gene which is involved in GABA biosynthesis inhibited ethylene production by reducing the enzyme activities of ACO and ACS, whereas silencing of AaGAD1 or AaGAD4 gene led to the reverse effect. On the other hand, overexpression of AaGAD1 or AaGAD4 decreased the expression levels of AaACO1 and AaACO3, AaACS1 and AaACS2, whereas silencing of AaGAD1 or AaGAD4 gene increased the expression levels of these four genes. Above all, our findings demonstrate that exogenous GABA treatment could improve the storage quality and extend the shelf life of kiwifruit, Additionally, the content of GABA was participated in the regulation of ethylene biosynthesis at the molecular level.