Semidwarfing genes have improved crop yield by reducing height， improving lodging resistance， and allowing plants to allocate more assimilates to grain growth. In wheat ()， the semidwarfing gene was identified and deployed in durum wheat before it was transferred into bread wheat， where it was shown to have agronomic potential. ， a dominant and gibberellin (GA) responsive mutant， is genetically and functionally distinct from the widely used GA-insensitive semidwarfing genes and In this study， the gene was identified by mutagenizing the semidwarf durum cultivar Icaro () and generating mutants with a range of tall phenotypes. Isolating and sequencing chromosome 6A of these "overgrowth" mutants showed that they contained independent mutations in the coding region of is predicted to encode a GA 2-oxidase that metabolizes GA biosynthetic intermediates into inactive products， effectively reducing the amount of bioactive GA (GA). Functional analysis of the GA2oxA9 protein demonstrated that GA2oxA9 converts the intermediate GA to the inactive metabolite GA Furthermore， showed higher expression of and lower GA content compared with its tall parent. These data indicate that the increased expression of in results in a reduction of both bioactive GA content and plant height. This study describes a height-reducing mechanism that can generate new genetic diversity for semidwarfism in wheat by combining increased expression with mutations of specific amino acid residues in .