The regulation of plant height formed the basis of the Green Revolution, which was associated with major yield increases in wheat and rice due to improved lodging resistance and better allocation of assimilates to grain growth. Proteins encoded by semi-dwarfing genes regulate the plant height by lowering the bioactive content of gibberellins (GAs) or by inhibiting GA signalling. Rht18 is a dominant gibberellin-responsive semi-dwarfing phenotype that was identified in 1980s following fast neutron mutagenesis of the tall durum wheat variety Anhinga and released as the commercial semi-dwarf cultivar Icaro. The gene underlying the dwarfism has been genetically mapped to Triticum durum chromosome 6A. Comparative analysis of 6A sequences from the semi-dwarf Icaro and its five overgrowth mutants, obtained after sodium azide treatment, revealed GA2oxA9 as the gene underlying the height trait1. The gene codes for GA2-oxidase that metabolizes GA biosynthetic intermediates and thus reduces the amount of bioactive GA (GA1). The transcript levels of GA2oxA9 were higher, and the GA1 content lower in semi-dwarf Icaro compared with its tall parent Anhinga but no difference in coding sequence and promoter region has been observed. Analysis of a reconstructed 100-kb upstream region in both cultivars indicated multiple SNPs between Icaro and Anhinga but no remarkable structural variation explaining the increased expression of GA2oxA9 in Icaro. Aiming to reveal the causative of the expression increase and the semi-dwarf Icaro phenotype, we are approaching the wider GA2oxA9 region in Icaro and Anhinga by nanopore and bisulfite sequencing of flow-sorted 6A chromosomes, mapping chromatin accessibility by ATAC-seq and applying ChIP of histone modifications at regulatory elements. Combination of these techniques is expected to provide comprehensive information at both genetic and epigenetic level and potentially reveal long-distance regulatory elements impacting the GA2oxA9 expression.