Extragenic suppressors of the Arabidopsis gai mutation alter the dose-response relationship of diverse gibberellin responses

Active gibberellins (GAs) are endogenous factors that regulate plant growth and development in a dose-dependent fashion. Mutant plants that are CA deficient, or exhibit reduced GA responses, display a characteristic dwarf phenotype. Extragenic suppressor analysis has resulted in the isolation of Arabidopsis mutations, which partially suppress the dwarf phenotype conferred by GA deficiency and reduced CA-response mutations. Here we describe detailed studies of the effects of two of these suppressors, spy-7 and gar2-1, on several different CA-responsive growth processes (seed germination, vegetative growth, stem elongation, chlorophyll accumulation, and flowering) and on the in planta amounts of active and inactive CA species. The results of these experiments show that spy-7 and gar2-1 affect the GA dose-response relationship for a wide range of GA responses and suggest that all CA-regulated processes are controlled through a negatively acting CA-signaling pathway.