Dwarf plants of diploid Medicago sativa carry a mutation in the gibberellin 3-β-hydroxylase gene

In this paper we describe the identification of a gene, MsDWF1 coding for a putative gibberellin 3-β-hydroxylase (GA3ox), whose natural mutation is conditioning a dwarf growth phenotype in Medicago sativa . The dwarf phenotype could not be complemented with grafting, which indicates that the bioactive gibberellin compound necessary for shoot elongation is immobile. On the contrary, exogenously added gibberellic acid restored normal growth. The genetic position of the Msdwf1 gene was mapped to linkage group 2 (LG2) and the physical location was delimited by map-based cloning using Medicago truncatula genomic resources. Based on the similar appearance and behavior of the dwarf Medicago sativa plants to the pea stem length mutant ( le ) as well as the synthenic map position of the two genes it was postulated that MsDWF1 and pea Le are orthologs. The comparison of wild type and mutant allele sequences of MsGA3ox revealed an amino acid change in a conserved position in the mutant allele, which most probably impaired the function of the enzyme. Our results indicate that the dwarf phenotype was the consequence of this mutation.