Abstract: In this study，four AP2/ERF family genes named PhAP2/ERF1–PhAP2/ERF4 were cloned from the leaves of the Phalaenopsis‘Big Chili’by RT-PCR. Each PhAP2/ERF1–PhAP2/ERF4 contained an AP2 domain whereas the PhAP2/ERF2 also contained a B3 domain. The phylogenetic tree analysis showed that PhAP2/ERF1–PhAP2/ERF4 was closely related to members of AP2/ERF family in Orchidaceae. In addition，we found that the PhAP2/ERF1 belonged to the A1 group of DREB subfamily in AP2/ERF family，PhAP2/ERF2 belonged to RAV subfamily，PhAP2/ERF3 belonged to the B4 group of ERF subfamily，and PhAP2/ERF4 belonged to the A2 group of DREB subfamily. Real-time fluorescence quantitative PCR was used to investigate the expression levels of PhAP2/ERF1–PhAP2/ERF4 in the leaves of Phalaenopsis‘Big Chili’and Phalaenopsis‘Fuller’s Sunset’under low temperature acclimation and low temperature stress. The results showed that the expression of four PhAP2/ERF genes have the same trend in leaves of‘Big chili’，with the highest level at the early stage and decreased slightly at the middle and late stages after low temperature stress treatment. However，the expression levels of four PhAP2/ERF genes showed the significant differences trends in the leaves of Phalaenopsis‘Fuller’s Sunset’. The expression levels of PhAP2/ERF1 and PhAP2/ERF2 were not induced or increased slightly during the low temperature treatment. Moreover，the response time of PhAP2/ERF3 in leaves of Phalaenopsis‘Fuller’s Sunset’noticeably lagged behind that of Phalaenopsis‘Big Chili’under low temperature. There was little difference of PhAP2/ERF4 between Phalaenopsis‘Fuller’s Sunset’and Phalaenopsis‘Big Chili’. The difference in the expression of AP2/ERFs in the leaves between cold- resistant variety Phalaenopsis‘Big chili’and nonresistant variety Phalaenopsis‘Fuller’s Sunset’suggested that the AP2/ERF gene family of Phalaenopsis hybrida plays an important role in the regulation of low temperature stress response in Phalaenopsis species.

Key words: Phalaenopsis, low temperature stress, AP2/ERF gene, gene clone, expression analysis