A novel dwarfing mutation in a 'Green Revolution' gene in Brassica rapa: Its role in the gibberellin pathway and its potential use in agriculture

Lodging is a serious problem in oilseed Brassica napus. In wheat and rice, dwarf genes have been used to reduce lodging, and their use was a major factor in the success of the 'Green Revolution'. A dwarf gene, dwf2, from B. rapa was characterized as a gibberellin insensitive, semi-dominant allele at a single locus, and it significantly reduced plant height in field experiments. Comparative mapping analysis suggested that a homolog of Arabidopsis RGA ( repressor of gal-3), encoding a DELLA protein, which is a homolog of the wheat 'Green Revolution' gene, was a candidate for the mutant gene. DWF2 was cloned and renamed BrRGA1. dwf2 (Brrga1-d) mutant contains one base pair substitution changing an absolutely conserved amino acid in the C-terminus of BrRGA1. This mutation results in high levels of accumulation of Brrga1-d protein, which is resistant to degradation by gibberellin. Transgenic Arabidopsis plants expressing AtRGA with an identical mutation as in Brrga1-d, Atrga-d , are dwarfs with high levels of accumulation of GA-resistant Atrga-d protein, indicating that the effect of the mutation is conserved in other species. Results from yeast two hybrid assays suggested that the dwarf phenotypes caused by high levels of accumulation of the mutant protein is due to the inability of the mutant proteins to interact with SLY1, a component needed for the degradation process. The Brrga1-d allele transferred to B. napus, using interspecific hybridization and embryo rescue, significantly reduced plant height and lodging of B. napus inbred and hybrid lines. A 'perfect' PCR marker based on detecting the nucleotide mutation causing the dwarf phenotype was developed for selecting the Brrga1-d gene in B. napus and B. rapa breeding programs.