Molecular Cloning, Structural Characterization, and Ripening-Related Expression of Lipoxygenase Genes from Three Persimmon Cultivars Differing in Postharvest Ripening Rate

Abstract

A novel lipoxygenase (LOX) gene, DkLOX4 (KF035132), and the full-length DkLOX3 (KF035131) gene were identified from persimmon fruit, and transcriptional profiles of both genes in three persimmon cultivars with different ripening rates were investigated using quantitative real-time PCR (qRT-PCR). We also studied their expression in response to propylene and 1-methylcyclopropene (1-MCP), which can promote or impede fruit ripening. Phylogenetic analysis indicated that both DkLOX3 and DkLOX4 belong to the 9-LOX family. The identity of these DkLOX genes was confirmed by functional expression in bacteria. The results showed that both DkLOX3 and DkLOX4 possessed the expected LOX activity. qRT-PCR analysis showed that all DkLOX genes were expressed abundantly in persimmon fruit during ripening, but distinctly different expression patterns were evident. Expression patterns of all DkLOXs generally paralleled the climacteric rise and maxima in ethylene production. The trajectories of transcript accumulation and the expression peaks also paralleled the declines in fruit firmness and increase in LOX activity and malondialdehyde (MDA) content. The expression level of DkLOX3 was significantly higher than that of the other two DkLOXs, its expression maxima followed the order from high to low and early to late in ‘Fupingjianshi’, ‘Huoshi’ and ‘Ganmaokui’. And expression of DkLOX3 was particularly up-regulated by propylene treatment, and down-regulated by 1-MCP treatment. Overall, the results reported here indicate that LOX genes, especially DkLOX3, may play an important role in persimmon fruit ripening.