Abstract
A novel gibberellin (GA)-deficient mutant designated dwarf and delayed-flowering 1 (ddf1) was isolated from a library of activation-tagged Arabidopsis. Genetic and molecular analyses revealed that the ddf1 mutation is caused by increased or ectopic expression of a putative AP2 transcription factor. Gene expression analysis showed that a gene for catabolite enzyme GA 2-oxidase is highly induced, but genes for biosynthetic enzymes are not repressed in a 35S::DDF1 plant. Interestingly among (putative) AP2 transcription factors in Arabidopsis, DDF1 are phylogenetically close to DREB1/CBF, which are known to be involved in stress responses. The transcripts of DDF1 and the gene for GA 2-oxidase are induced by high-salinity and drought stresses. Moreover, transgenic plants overexpressing DDF1 show increased tolerance to high-salinity stress. These suggest that Arabidopsis induce GA 2-oxidase by environmental stresses as a stress response.
