Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 3/30/2006
Publication Date: 7/7/2006
Citation: Whitaker, B.D., Lester, G.E. 2006. Phospholipase D-alpha and lipoxygenase gene expression in fruit, floral, and vegetative tissues of ‘Honey Brew’ hybrid honeydew melon [abstract]. Hort Science. 41(4):1081. Interpretive Summary:
Technical Abstract: Increases in phospholipase D (PLD) and lipoxygenase (LOX) activities are thought to play a critical role in senescence of mesocarp tissues in netted and nonnetted muskmelon (Cucumis melo L.) fruits. We have cloned and characterized two full-length cDNAs, CmPLDa1 and CmLOX1, encoding PLD-alpha and LOX proteins in honeydew melon (C. melo L. Inodorus Group cv. Honey Brew). Relative levels of expression of the corresponding genes were determined by semi-quantitative RT-PCR in developing and mature fruit mesocarp tissues (20–60 d after pollination; DAP), as well as in roots, leaves, and stems from 4-week-old and flowers from 6- to 7-week-old plants. The coding regions of CmPLDa1 and CmLOX1 cDNAs are, respectively, 2427 and 2634 nucleotides long, encoding proteins 808 and 877 amino acids in length. CmPLDa1 is very similar to PLD-alpha genes from castor bean, cowpea, strawberry, and tomato (77% nucleotide identity), and is the first PLD gene cloned from a cucurbit species. CmLOX1 has 94% nucleotide identity to a cucumber (C. sativus L.) LOX gene expressed in roots and 80% identity to cucumber cotyledon lipid body LOX. In general, transcript of CmPLDa1 was much more abundant than that of CmLOX1, but relative levels of transcript in the various organs and tissues were similar for the two genes. Expression was highest in roots, flowers, and fruit mesocarp tissues. CmPLDa1 expression in fruit was essentially constitutive throughout development, although maximum levels occurred at 50 and 55 DAP, respectively, in middle and hypodermal mesocarp. CmLOX1 expression was generally higher in middle than in hypodermal mesocarp with maximum transcript levels occurring at 55 and 50 DAP, respectively. Overall, the patterns of expression of CmPLDa1 and CmLOX1 are consistent with a model in which their encoded enzymes act in tandem to promote or accelerate senescence in fruit mesocarp tissues.