Discovery of genes for fragrance and nutritional traits in rice

The appeal of rice to human consumers is influenced by the texture of the cooked rice and the flavour or fragrance of the 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 or Jasmine (Thai) style rices. This attribute had been associated with a gene on chromosome 8. Sequencing of the genes in this chromosome region revealed that fragrance was caused by a deletion of 8bp resulting in the loss of function of a gene encoding an aldehyde dehydrogenase. Fragrance in rice appears to be the result of a common mutation event in all fragrant varieties. 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 resulted a loss of about 8 C in gelatinization temperature. Selection for cooking quality in the domestication of rice may have contributed to the selection of rice varieties with a higher GI.