Molecular Characterization of High Protein Rice Lines.

Protein content is an important part of nutritional values of rice.  Various approaches have been used to increase grain protein content and improve essential amino acid compositions in grain crops.  Among them are  induced mutations to improve protein content in general or enhance amino acids of a specific target, transgene technology to alternative biochemical pathways causing elevated accumulation of grain protein content, and molecular breeding and map-based cloning to maximize the use of natural genetic variation to improve protein content in the breeding process.  The objectives of this study were to (1) conduct molecular characterization of high protein lines through their sequence differences of the dihydrodipicolinate synthase (DHDPS) gene and (2) develop marker profiles associated with high grain protein content.  DHDPS gene sequence of eight high protein rice lines that have a significant increase in lysine and threonine contents show two polymorphic regions that could attribute to their elevated levels of these two essential amino acids in the grain.  The differences in the nucleotide sequence cause the alteration of amino acid residues within the DHDPS gene.  Such alteration may decrease its sensitivity to the feedback inhibition, causing significant accumulation of these two amino acids.  Molecular tagging using a set of closely related lines differ in their grain protein content identified genomic regions that control 60% of the total high protein expression.