GIBBERELLINS REGULATE THE ABUNDANCE OF RNAS WITH SEQUENCE SIMILARITY TO PROTEINASE-INHIBITORS, DIOXYGENASES AND DEHYDROGENASES

In an effort to understand the molecular mechanism of gibberellin (GA) action, we have cloned and performed an initial characterization of t hree cDNAs (GAD1, 2, and 3) which correspond to RNAs that become less abundant by 2 h after treatment of tomato (Lycopersicon esculentum Mil l.) shoot tissue with gibberellic acid (GA(3)). Treatment with either auxin or ethephon also decreases the abundance of all three of the GAD RNAs. The tomato ethylene-insensitive mutant, Nr, and the GA-deficien t mutant, gib1, were used to show that GA or auxin regulation of GAD R NA abundance is not dependent on ethylene sensitivity, and that ethyle ne or auxin regulation is not dependent on normal levels of gibberelli n biosynthesis. Treatment with abscisic acid (ABA) antagonizes the GA- induced suppression of the GAD1 and GAD2 RNAs. GAD1 is similar to type -II wound-inducible plant proteinase inhibitors. Like the well-charact erized proteinase inhibitor II (pin II) of tomato, the GAD1 and GAD2 R NAs are wound inducible. Induction of pin II and GAD1 RNA in gib1 was found to require less-severe wounding than was required using wild-typ e plants or plants doubly mutant for gib1 and sir (the sit mutation ca uses ABA deficiency). The predicted GAD2 protein sequence is similar t o 2-oxoglutarate-dependent dioxygenases while the predicted GAD3 prote in sequence is similar to proteins belonging to the nonmetallo-short-c hain alcohol-dehydrogenase family, especially the TASSELSEED2 (TS2) ge ne of maize and bacterial hydroxysteroid dehydrogenases.