Accumulation of Phosphorylated Repressor for Gibberellin Signaling in an F-Box Mutant

Gibberellin (GA) regulates growth and development in plants. We isolated and characterized a rice GA-insensitive dwarf mutant, gid2. The CID2 gene encodes a putative F-box protein, which interacted with the rice Skp1 homolog in a yeast two-hybrid assay. In gid2, a repressor for GA signaling, SLR1, was highly accumulated in a phosphorylated form and GA increased its concentration, whereas SLR1 was rapidly degraded by GA through ubiquitination in the wild type. We conclude that GID2 is a positive regulator of GA signaling and that regulated degradation of SLR1 is initiated through GA-dependent phosphorylation and finalized by an$SCF^{GID2}-proteasome$pathway.