Isolation and expression analysis of three EIN3-like genes in tree peony (Paeonia suffruticosa)

Ethylene is a critical signal that influences cut flower opening and senescence in tree peony (Paeonia suffruticosa), which is a traditional ornamental plant in China. Arabidopsis ETHYLENE-INSENSITIVE3 (EIN3) acts as a key transcription factor of the ethylene signaling pathway, suggesting a possible role for its homologues in regulation of cut flower postharvest development. In this study, three EIN3 homologous genes including PsEIL1, PsEIL2, and PsEIL3 have been isolated from petals of tree peony. Deduced amino acid sequences of conserved domains of PsEILs share high similarities with the Arabidopsis EIN3 protein. Real-time reverse transcription-polymerase chain reaction (RT-PCR) analysis indicated that three PsEILs were differentially expressed in various tissues of tree peony, and none was flower specific. During cut flower postharvest development, PsEIL1 transcript in petals accumulated at a relatively low level at the opening stage and reached the highest level of mRNA accumulation at senescence; PsEIL2 and PsEIL3 transcripts were gradually increased and peaked at full opening stage followed by a decline when petals wilted. However, these PsEIL genes exhibited differential responses to ethylene and 1-methycyclopropene (1-MCP) treatments. Compared with the control, the mRNA level of PsEIL1 was not influenced by either ethylene or 1-MCP treatment, whereas both PsEIL2 and PsEIL3 transcripts were significantly increased by exogenous ethylene, and only PsEIL3 was strongly inhibited by 1-MCP. These results suggest that PsEIL transcripts are spatiotemporally regulated, and the transcriptional regulation of PsEIL3 may play an important role in ethylene-mediated cut flower opening and senescence in tree peony.