Rice gibberellin-insensitive dwarf mutant gene Dwarf 1 encodes the α-subunit of GTP-binding protein

A rice Dwarf 1 gene was identified by using a map-based cloning strategy. Its recessive mutant allele confers a dwarf phenotype. Linkage analysis revealed that a cDNA encoding the cr-subunit of GTP-binding protein cosegregated with dl in 3,185 dl segregants. Southern hybridization analysis with this cDNA as a probe showed different band patterns in several dl mutant lines. In at least four independent dl mutants, no gene transcript was observed by Northern hybridization analysis, Sequencing analysis revealed that an 833-bp deletion had occurred in one of the mutant alleles, which resulted in an inability to express GTP-binding protein, A transgenic dl mutant with GTP-binding protein gene restored the normal phenotype. We conclude that the rice Dwarf I gene encodes GTP-binding protein and that the protein plays an important role in plant growth and development. Because the dl mutant is classified as gibberellin-insensitive, we suggest that the GTP-binding protein might be associated with gibberellin signal transduction.