Vol. 82 No: 1

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

Authors:
D.P. MAUL, W. McKENDREE, M. BAUSHER and T.G. McCOLLUM

pp: 61-68

Abstract:
The role of ethylene in citrus fruit physiology is poorly understood. Gene expression studies with ethylene and ethylene inhibitors suggest a regulatory role for the low basal levels of endogenous ethylene in citrus fruits; however, only a few ethylene-modulated genes have been reported. 1-Methylcyclopropene (1-MCP), an ethylene antagonist that inhibits ethylene signal transduction by preventing ethylene from binding to its receptors, is a useful tool to further identify genes associated with the regulatory roles of ethylene. We determined the effects of ethylene and 1-MCP on gene expression in grapefruit flavedo. Total RNA from fruit treated with air, 5 µl l^-l ethylene, or 0.3 µl l^-l 1-MCP for 48 h was used in differential-display reverse transcription-polymerase chain reaction (DD-RT-PCR) analysis. Our hypothesis was that genes whose expression is induced by ethylene would be up-regulated in response to ethylene, whereas genes whose expression is inhibited by ethylene would be up-regulated in response to 1-MCP.A 440 bp cDNA, induced by ethylene, was used as a probe to screen a cDNA library of flavedo, and obtain a clone with a deduced amino acid sequence 88% similar to the enzyme phosphoenolpyruvate carboxykinase (PEPCK, EC 4.1.49) from both Arabidopsis and Flaveria trinervia. We designated this gene CpPEPCK (Citrus × paradisi phosphoenolpyruvate carboxykinase). Northern blot and RT-PCR analyses revealed increased expression of CpPEPCK in grapefruit flavedo after exposure to ethylene, and with increased exposure time. In contrast, treatment with 1-MCP inhibited the accumulation of CpPEPCK transcripts in the same tissue. Although CpPEPCK is expressed in leaves, roots, and petals, higher transcript abundance was found in the flavedo of ethylene-treated fruit than in other tissues. This study provides additional evidence for a role for ethylene in citrus fruit physiology.

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