Characterization of β-Galactosidase Genes Involved in Persimmon Growth and Fruit Ripening and in Response to Propylene and 1-Methylcyclopropene

Abstract

Fruit cell wall modification is the main factor affecting fruit softening. β-Galactosidase (EC 3.2.1.23) is one of the cell wall modifying enzymes that are involved in fruit ripening. Although β-galactosidase genes have been characterized in multiple fruits, the relationship between β-galactosidase genes and persimmon (Diospyros kaki) ripening remains unknown. In this study, four persimmon β-galactosidase genes, designated DkGAL1 to DkGAL4, were isolated from ‘Fupingjianshi’ persimmon fruit. Transcriptional profiles of DkGAL genes during fruit development and in response to ethylene were investigated. β-Galactosidase activity increased during postharvest ripening and was considerably induced by propylene. The accumulation of DkGAL1 was relatively low during fruit growth but significantly increased throughout fruit ripening. In contrast, DkGAL2 mRNA levels were the highest at the early phase of fruit growth and decreased towards fruit maturity. DkGAL3 and DkGAL4 exhibited very low levels of expression in both growing fruit and postharvest fruit but were predominantly expressed in the leaf and stem. The expression pattern of DkGAL1 was positively regulated by ethylene, up-regulated under propylene treatment and suppressed by 1-MCP treatment. Ethylene appears to have little effect on the transcription of DkGAL2, DkGAL3 and DkGAL4. These results demonstrate that multiple β-galactosidase genes have differential transcript and hormonal regulation characteristics in ripening persimmon fruit. The functions of DkGAL3 and DkGAL4 are limited in fruit. However, DkGAL2 may play a crucial role in fruit development. Furthermore, DkGAL1 is a predominant β-galactosidase gene that is involved in persimmon fruit softening and regulated by ethylene.