CHARACTERIZATION OF AN ETHYLENE-REGULATED FLOWER SENESCENCE-RELATED GENE FROM CARNATION

The programmed senescence of carnation (Dianthus caryophyllus L.) petals requires active gene expression and is associated with the expression of several senescence-related mRNAs. Expression of the mRNA represented by the cDNA clone pSR12 has previously been shown to be transcriptionally activated by ethylene specifically in senescing flowers. We report in this paper the structural analysis of this cDNA and its corresponding gene. One cloned genomic DNA fragment, SR12-B, contained the entire transcription unit in 17 exons, interrupted by 16 introns. A second gene, SR12-A, was highly homologous to SR12-B with several nucleotide substitutions and a 489 bp deletion in the 5' flanking DNA sequence. The SR12 transcript has an open reading frame of 2193 bp sufficient to encode a protein of 82.8 kDa. No significant homology at the DNA or protein levels was found with other known genes. We have identified a DNA-binding factor which specifically interacts with two upstream fragments (-149 to -337 and -688 to -1055) of SR12-B. Both fragments apparently compete for the same binding factor. The DNA-binding activity was present in nuclear extracts from both presenescent and senescing carnation petals. The upstream DNA fragments that bind this factor have sequence homology with promoter sequences of other ethylene-regulated genes.