Abstract: The cucumber foliage bitterness gene（Bi）encodes a cyclase and is responsible for the first committed step in the biosynthesis of cucurbitacin C. We cloned Bi gene promoter from North China cucumber‘9930’. To identify the candidate transcript factor that could regulate its expression in cucumber，we applied yeast one hybrid system using the promoter of Bi as bait to screen a cDNA library generated from cucumber leaves. After the sequencing of positive signals and alignment with cucumber genome database，we identified seven TFs（2 AP2/ERF，3 bZIP，1 WRKY and 1 E3 ubiquitin class）that were repeatedly detected from the sequencing results. CsERF（Accession number：Csa7M448110），the AP2/ERF family TF，was selected for a further study as repeated six times more than other TFs. In addition to the yeast one-hybrid system，we also observed the similar result using the transient expression system in tobacco. In summary，yeast one-hybrid and tobacco transient expression system showed that the CsERF has the ability to activate the transcription of Bi. Thus，this gene was an important candidate regulator that could control the biosynthesis of bitter material in cucumber.

Key words: cucumber, bitterness, yeast one hybrid, tobacco transient expression, AP2/ERF transcription factor