Effects of postharvest treatments on expression of three lipoxygenase genes in oriental melon (Cucumis melo var. makuwa Makino)

Abstract

In order to investigate the effects of different postharvest treatments on the expression of lipoxygenase (LOX) genes in oriental melon (Cucumis melo var. makuwa Makino) fruit, three LOX genes (CmLOX03, CmLOX09, and CmLOX18) were cloned and the patterns of transcript abundance during postharvest storage were measured. Phylogenetic analyses indicated that CmLOX03, CmLOX09, and CmLOX18 represented three major LOX groupings: type1 13-LOXs, type1 9-LOXs, and type2 13-LOXs, respectively. The transcriptional regulation of CmLOX03, CmLOX09, and CmLOX18 and the physiological and biochemical changes that occur during postharvest melon fruit ripening were characterized. Quantitative real-time PCR (qPCR) showed that the expressions of CmLOX03 and CmLOX18 were up-regulated by ethylene treatment, following a pattern similar to that of LOX enzyme activity, and corresponding to changes in soluble solids content (SSC), the softening process, color changes, and ethylene production. By contrast, CmLOX09 transcript was negatively associated with the physiological and biochemical changes that occur during postharvest ripening. Treatments of 1-methylcyclopropene (1-MCP), ethanol, and low temperatures decelerated the ripening process and down-regulated the expression of both CmLOX03 and CmLOX18, while CmLOX09 had no such effects under the three treatments. In summary, these findings imply that CmLOX03 and CmLOX18 might be major LOX-encoding genes involved in melon fruit ripening, and that individual CmLOX isoforms are differentially regulated and have distinct functions during the postharvest ripening of melons.