The DDF1 transcriptional activator upregulates expression of a gibberellin-deactivating gene, GA2ox7, under high-salinity stress in Arabidopsis.

High-salinity stress affects plant growth and development. We have previously reported that overexpression of the salinity-responsive DWARF AND DELAYED FLOWERING 1 (DDF1) gene, encoding an AP2 transcription factor of the DREB1/CBF subfamily, causes dwarfism mainly by levels of reducing bioactive gibberellin (GA) in transgenic Arabidopsis. Here, we found that the GA 2-oxidase 7 gene (GA2ox7), which encodes a C20-GA deactivation enzyme, is strongly upregulated in DDF1-overexpressing transgenic plants. A loss-of-function mutation of GA2ox7 (ga2ox7-2) suppressed the dwarf phenotype of DDF1-overexpressing plants, indicating that their GA deficiency is due to overexpression of GA2ox7. Transient overexpression of DDF1 activated the promoter of GA2ox7 in Arabidopsis leaves. A gel shift assay showed that DDF1 binds DRE-like motifs (GCCGAC and ATCGAC) in the GA2ox7 promoter. In Arabidopsis under high-salinity stress, six GA2ox genes, including GA2ox7, were upregulated. Furthermore, the ga2ox7-2 mutant was less growth retarded than wild-type Col under high-salinity stress. These results demonstrate that, under salinity stress, Arabidopsis plants actively reduce endogenous GA levels via the induction of GA 2-oxidase, with the result that growth is repressed for stress adaptation.

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