Ethylene-responsive element-binding factor (ERF) genes constitute one of the largest transcription factor gene families in plants. In Arabidopsis and rice, only a few ERF genes have been characterized so far. Flower senescence is associated with increased ethylene production in many flowers. However, the characterization of ERF genes in flower senescence has not been reported. In this study, 13 ERF cDNAs were cloned from petunia. Based on the sequence characterization, these PhERFs could be classified into four of the 12 known ERF families. Their predicted amino acid sequences exhibited similarities to ERFs from other plant species. Expression analyses of PhERF mRNAs were performed in corollas and gynoecia of petunia flower. The 13 PhERF genes displayed differential expression patterns and levels during natural flower senescence. Exogenous ethylene accelerates the transcription of the various PhERF genes, and silver thiosulphate (STS) decreased the transcription of several PhERF genes in corollas and gynoecia. PhERF genes of group VII showed a strong association with the rise in ethylene production in both petals and gynoecia, and might be associated particularly with flower senescence in petunia. The effect of sugar, methyl jasmonate, and the plant hormones abscisic acid, salicylic acid, and 6-benzyladenine in regulating the different PhERF transcripts was investigated. Functional nuclear localization signal analyses of two PhERF proteins (PhERF2 and PhERF3) were carried out using fluorescence microscopy. These results supported a role for petunia PhERF genes in transcriptional regulation of petunia flower senescence processes.

Carnation (Dianthus caryophyllus L.) is an important ornamental crop and serves as a model system for investigating ethylene-sensitive flower senescence. EIN2 (ethylene insensitive 2) is a central component of the ethylene signal transduction pathway in plants, but the transcriptional regulation of the EIN2 gene in response to ethylene has not yet been elucidated. We identified a cDNA clone encoding a putative EIN2-like protein (DCEIN2) from total RNA isolated from senescing carnation petals using reverse transcription-PCR and rapid amplification of cDNA ends procedures. The cDNA contained an open reading frame of 3828 bp corresponding to 1275 amino acids. The northern blot results indicated that DCEIN2 expression in both the petals and ovaries was enhanced by treatment with exogenous ethylene and sugar, respectively, and was inhibited by silver thiosulfate. In the carnation vegetative tissues, mRNAs for DCEIN2 were present in the leaves and stems, but they were not detected in the roots.

RTE1 (REVERSION-TO-ETHYLENE SENSITIVITY1) was identified as a positive regulator of ETR1 (ethylene resistant1) function in Arabidopsis; RTEs are a small gene family. Ethylene plays a crucial role in the senescence of carnation (Dianthus caryophyllus L.) flowers. Two cDNA clones encoding putative RTE-like protein (DCRTE1 and DCRTH1) were obtained from total RNA isolated from senescing carnation petals using RT-PCR and RACE techniques. The predicted proteins of DCRTE1 and DCRTH1 consist of 228 and 233 amino acids, respectively. Interestingly, the deduced DCRTE1 protein, like most other RTEs, includes two putative transmembrane domains, while the deduced DCRTH1 protein includes five putative transmembrane domains, according to the TMHMM database. Northern blots showed that the level of DCRTE1 mRNA in petals first decreased then increased remarkably after ethylene production started, and DCRTE1 expression showed an increasing trend in ovaries during natural flower senescence. The amount of DCRTH1 transcripts increased gradually in both petals and ovaries during natural senescence. Exogenous ethylene increased transcript abundance of DCRTE1 and DCRTH1 to various degrees in both petals and ovaries. STS treatment decreased the level of DCRTH1 mRNA in petals and ovaries compared with the control. DCRTE1 and DCRTH1 showed a rapid increase and then a decrease in mRNA accumulation in leaves after wounding. These results suggest that both DCRTE1 and DCRTH1 could play important roles in flower senescence-related signalling. Sucrose treatment did not remarkably affect the amount of DCRTE1 and DCRTH1 mRNAs.

No abstract