Three different polygalacturonases are expressed in tomato leaf and flower abscission, each with a different temporal expression pattern

Abscission, or organ separation, is accompanied by a marked increase in hydrolases, which are responsible for the degradation of the middle lamella and the loosening of the primary cell wall surrounding cells in the separation layer. We recently reported on the cloning of a tomato (Lycopersicon esculentum) polygalacturonase (PG) cDNA, TAPG1, expressed during leaf and flower abscission. In addition to TAPG1, we have cloned two more PG cDNAs (TAPG2 and TAPG4) that are also expressed during leaf and flower abscission. The peptide sequences for the three abscission PGs are relatively similar (76-93% identity) yet different from the those of tomato fruit PG (38-41% identity). None of the three abscission PG mRNAs are expressed in fruit, stems, petioles, or anthers of fully open flowers. An RNase protection assay revealed that all three PGs are expressed in leaf and flower abscission zones and in pistils of fully open flowers. TAPG4 mRNA is detected much earlier than TAPG1 and TAPG2 mRNA during both leaf and flower abscission.