Ethylene modulates transcription of the phosphoenolpyruvate carboxykinase gene in grapefruit flavedo

Abstract

Listen

Translate article

SummaryThe 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.