THE GENE PROMOTER FOR A BEAN ABSCISSION CELLULASE IS ETHYLENE-INDUCEDIN TRANSGENIC TOMATO AND SHOWS HIGH SEQUENCE CONSERVATION WITH A SOYBEAN ABSCISSION CELLULASE

Bean leaf abscission (organ separation) correlates with the de novo ac cumulation of a pI 9.5 cellulase and its mRNA. Overlapping genomic clo nes encoding the bean abscission cellulase (BAC) were isolated and par tially sequenced. In addition, a genomic clone for a soybean abscissio n cellulase (SAC) was identified and the sequence compared to the BAC genomic sequence. Two 5'-upstream regions are particularly well conser ved in the two sequences. Of special interest here is the region betwe en -1 and -200 in the BAC promoter which is highly conserved in the SA C gene. Particle gun bombardment with a BAC promoter construct contain ing 210 bp of BAC sequence 5' to the transcription start site was suff icient to drive abscission-specific and ethylene and auxin-regulated t ransient expression in bean. In addition to the transient expression a ssay, expression was examined in stably transformed tomato. A similar -210 bp BAC promoter construct supported a low level of ethylene-induc ible reporter gene expression in tomato leaf abscission zones and adja cent petioles but not in ethylene-treated stem tissue or fruit. Expres sion from the -210 promoter in tomato abscission zones was inhibited b y silver thiosulfate, an ethylene action inhibitor, and was partially inhibited by treatment with auxin.