Submitted to: Plant Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: February 21, 1998
Publication Date: N/A
Interpretive Summary: Abscission is the process by which plants shed organs such as leaves, flowers, and fruit. The enzymes cellulase and polygalacturonase (PG) are important in breaking down the cell wall surrounding plant cells. The breakdown of the cell walls allows the cells to separate from each other and form the separation layer. In this manuscript we report the cloning and DNA sequence of five PG genes from tomato. Four of these genes are expressed in leaf and flower abscission zones. The purpose of this study was to better understand the regulation and expression of PG in tomato so that scientists and biotechnologists can use this information to genetically engineer plants with beneficial abscission properties i.e., increased yield and quality.
Technical Abstract: Recently, three polygalacturonase (PG) cDNAs (TAPG1, TAPG2, and TAPG4) were identified in a library prepared from tomato (Lycopersicon esculentum cv. Rutgers) leaf abscission zones. Genomic clones encoding these three cDNAs have been identified. Moreover, the genomic clones include two additional PG genes, TPG3 and TAPG5, which have not been previously reported. Transcript for TAPG5 was detected in the RNA from leaf and flower abscission zones; however, transcript for TPG3 was not. DNA sequence analysis reveals that TAPG1, TAPG2, and TPG3 are linked in a close tandem array. TAPG4 and TAPG5 are also closely linked to each other but in a divergent orientation and are not linked to TAPG1, TAPG2, or TPG3. TAPG4 and TAPG5 map to the middle of chromosome twelve. All five PG genes include four exons and three introns. The relative positions of introns 1, 2 and 3 are conserved with introns 4, 6 and 8 in the gene for the tomato fruit PG. Of special interest is an approximately 300 bp inverted repeat found in TAPG1, TAPG2 and TAPG4 that shares significant sequence identity with sequence in the first intron of the tomato anionic peroxidase gene, tap1. Transcript for an anionic peroxidase increases during abscission but the hormonal regulation of its expression is different from that of the TAPG genes. In addition, a 250 bp sequence found in TPG3 shares high sequence identity with a 5' upstream region in a wound-induced win2 gene from potato. Potential sites of transcriptional regulation in these genes are discussed.