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Title: Ethylene modulates transcription of the phosphoenolpyruvate carboxykinase gene in grapefuit flavedo.

Author
item Maul, Dora
item MCKENDREE, WILLIAM - US AIRFORCE
item Bausher, Michael
item McCollum, Thomas

Submitted to: Journal of Horticultural Science and Biotechnology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/17/2006
Publication Date: 1/15/2007
Citation: Maul, D.P., Mckendree, W., Bausher, M.G., Mccollum, T.G. 2007. Ethylene modulates transcription of the phosphoenolpyruvate carboxykinase gene in grapefuit flavedo. Journal of Horticultural Science and Biotechnology. 82:61-68.

Interpretive Summary: Ethylene is a gaseous plant hormone that regulates many aspects of plant growth and development. Although ethylene is used extensively in the citrus industry to degreen fruit, little is know about the role of ethylene in citrus fruit development and senescence. We conducted experiments to determine the effects of ethylene on gene expression in grapefruit rind. Fruit were treated with either ethylene or 1-methylcyclopropene (1-MCP), a compound that blocks the perception of ethylene. By treating fruit with either ethylene or 1-MCP we were able to compare the effects of added ethylene with the effects of no perception of ethylene. Using a technique known as differential display reverse transcription polymerase chain reaction analysis we identified a number of genes whose expression was either induced or repressed by ethylene. One of the genes was characterized and found to be homologous to a gene coding for the enzyme phosphoenol pyruvate carboxykinase. Interestingly, this gene has been found to be induced by ethylene in ripening tomato fruit. Results of this study provide new information regarding the role of ethylene in citrus fruit development.

Technical Abstract: The stimulatory effect of ethylene in gene expression during ripening of climacteric fruit is well established. In contrast, the role of this hormone in ripening of non climacteric fruit has remained elusive. To gain insight into the role of ethylene during maturation of grapefruit (Citrus paradisi, Macf.), a non climacteric fruit, differential display was performed using RNA isolated from flavedo (outer portion of the rind) of ethylene- and 1-MCP-treated grapefruit, 72 h after treatment. One of the ethylene-induced cDNAs, designated HAP3-4, was used to screen a flavedo library and after sequencing, revealed a 83% homology to the enzyme phosphoenolpyruvate carboxykinase (PEPCK, EC 4.1.49) from both tomato and Flaveria trinervia. RT-PCR analysis shows that this gene is expressed in grapefruit leaves, roots, petals and flavedo but higher expression occurs after exposure of fruits to ethylene. Treatments with 1-MCP repress accumulation of transcripts in flavedo. Time point course analysis shows increase in ethylene induction with time of exposure to this hormone. This study supports previous research suggesting a regulatory role for ethylene in citrus fruit and provides further evidence that climacteric and non-climacteric fruits may share common signaling pathways during ripening.