Expression of arabidopsis GAI in transgenic rice represses multiple gibberellin responses

Bioactive gibberellins (GAs) are essential endogenous regulators of plant g rowth. GA signaling is mediated via GAI, a nuclear member of the GRAS famil y of plant transcription factors. Previous experiments have suggested that GAI is a GA-derepressible repressor of plant growth. Here we test this hypo thesis by examining the effects of the expression of Arabidopsis GAI in tra nsgenic Basmati rice. High-level expression of GAI caused dwarfism and redu ced GA responses, and the strength of this effect was correlated with the l evel of transgene expression. In particular, the expression of GAI abolishe d the GA-mediated induction of rice aleurone alpha -amylase activity, thus implicating GAI orthologs in the well-characterized cereal aleurone GA resp onse. The GA derepressible repressor model predicts that high-level express ion of GAI should confer dwarfism, and these observations are consistent wi th this prediction.