Discovery of genes for quality and nutritional traits in rice

The appeal of rice to human consumers is influenced by the flavour or fragrance, and the texture of the cooked rice. Genes for both these traits have now been discovered. The recent availability of a complete high quality rice genome sequence has simplified the task of gene discovery in rice. The genetic basis of key quality traits may now be investigated by analysis of differences in the sequence of genes or genome regions associated with the traits. Fragrance of rice is very important in Basmati (Indian) and Jasmine (Thai) style rices. This attribute had been associated with a gene on chromosome 8. Sequencing of the genes in this chromosome region revealed fragrance is caused by a deletion of 8 bp in a gene encoding an aldehyde dehydrogenase resulting in the loss of function (Bradbury et al., 2005a). Fragrance in rice appears to be the result of a common mutation event in all fragrant varieties. Routine and robust selection tools for this trait are now available (Bradbury et al., 2006b). The gelatinization temperature of rice was known to be linked to a region encoding a starch synthase gene. DNA sequence variations resulting in two different amino acid substitutions in the encoded protein both result in a gelatinization temperature decrease of about 8 C (Waters et al., 2006). Selection for cooking quality in the domestication of rice may have contributed to the selection of rice varieties with a higher GI. New molecular selection tools allow high through put screening of rice lines for a wide range of important traits (Kennedy et al., 2006).