The phylogeny and expression profiles of the lipoxygenase (LOX) family genes in the melon (Cucumis melo L.) genome

- Eighteen candidate LOX genes in the melon genome were identified.
- Eighteen LOXs cluster into type type I 9-LOX, type I 13-LOX and type II 13-LOX.
- Sixteen CmLOXs were expressed in both vegetative and reproductive tissues.
- Three LOX genes seem to be associated with later development events.
- The possible roles of each LOX family member in melon are discussed.

Lipoxygenases (LOXs) are a group of non-haem iron-containing dioxygenases that have diverse and important functions in cells. Recent completion of the melon genome sequence permits us to analyze the LOX gene family in melon as well as comparison with LOX in Arabidopsis, tomato and cucumber. We identified 18 candidate LOX genes in the melon genome and found all LOX sequences indicating the importance of the functional domains of LOXs. The melon LOXs were divided by phylogenetic analysis into three categories: type I 9-LOX, type I 13-LOX, and type II 13-LOX. The gene expression analysis based on the semi-quantitative reverse transcription polymerase chain reaction (RT-PCR) and quantitative real-time PCR (qPCR) revealed that the 18 CmLOX genes exhibited a complex pattern. Sixteen genes of the 18 CmLOX genes were detected in both vegetative and reproductive tissues of the oriental sweet melon cultivar “Yumeiren”. Only CmLOX15 was expressed in vegetative tissues, while CmLOX07 was expressed in neither vegetative nor reproductive tissues. Eight of the 18 LOX genes expressions reached their peaks at 5 days after pollination (DAP) of the fruit. The total LOX activity and the expressions of three genes increased from 30 DAP to 40 DAP. After the volatiles were measured by gas chromatography-mass spectrometry (GC-MS), we found that ethyl and butyl acetates increased as the fruit ripened; however, the alcohol and aldehyde contents decreased from 30 to 40 DAP, implying that some CmLOX genes might be involved in volatile generation in the oriental melon. These results suggested that the 18 CmLOX genes were differentially regulated during melon development and ripening.