CLONING OF A TOMATO POLYGALACTURONASE EXPRESSED IN ABSCISSION

Abscission, organ separation, is accompanied by cell wall breakdown in separation layer cells. In tomato (Lycopersicon esculentum), ethylene -induced abscission is correlated with an increase in polygalacturonas e (PG) and endo-beta-1,4-D-glucanase (cellulase) activity. We have;ide ntified a putative, abscission-specific cDNA clone for PG, pTAPG1. The TAPG1 cDNA has 43% identity at the amino acid level with the tomato f ruit PG. Genomic blot analysis suggests that the gene for TAPG1 is a m ember of a small subfamily of PG genes that is distinct from the tomat o fruit PG. The TAPGI cDNA hybridizes to mRNA expressed during the cou rse of ethylene-induced leaf and flower abscission. A high level of PG transcript accumulation coincides with the occurrence of abscission. Auxin, an abscission inhibitor, and silver thiosulfate, an ethylene ac tion inhibitor, suppressed accumulation of mRNA in leaf abscission zon es complementary to the TAPG1 cDNA. Expression of TAPG1 transcripts is several-fold higher in flower abscission zones than in leaf abscissio n zones. The identification of cDNAs that encode abscission-specific P G provide and additional tool to study the regulation of abscission an d cell wall dissolution in separation layer cells.