Functional analysis of rice genes determining fragrance

The fragrance of rice has been associated with a deletion resulting in the apparent loss of function of a gene annotated as a betaine aldehyde dehydrogenase (BAD2) on chromosome 8. We have now compared the levels of expression of BAD2 and BAD1 (chromosome 4) from fragrant and non fragrant genotypes. Expression of BAD2 predominates in non fragrant genotypes but is reduced in genotypes with the fragrance allele. Expression of BAD1 and BAD2 proteins in bacteria was used to test the specificity of the reactions catalysed by these enzymes. This analysis suggests that BAD2 encodes a 4-aminobutyraldehyde dehydrogenase. Analysis of transgenic rice plants over-expressing these genes is in progress.