Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 11/20/2007
Publication Date: 12/29/2007
Citation: Mahmoud, A.A., Sukumar, S., Krishnan, H.B. 2007. An interspecific rice hydrid of Oryza sativa and Oryza nivara reveals a significant increase in seed protein content. Journal of Agricultural and Food Chemistry. 56:476-482. Interpretive Summary: Rice is currently considered as the world's single most important food crop for human consumption, being matched in its contribution to human diet only by that of wheat. Significant progress in improving rice yield is urgently needed in order to secure the growing global demands on food. Protein content of milled rice of modern cultivars is only about 7-9%, compared to 11-14% in wheat and oats and 8-11% in maize, barley, and sorghum. Strong efforts have been invested over the past five decades to improve protein content of rice. However, these efforts have been largely unsuccessful, as indicated by the lack of modern high protein rice cultivars. We have produced an interspecific hybrid between O. sativa and O. nivara which showed a significant increase in protein content compared to both parents. The results of our study demonstrate the potential of wild relatives of rice for the improvement of seed protein content. This interspecific rice hybrid could serve as the starting breeding material for the selection of new rice genotypes that combine the high yield potential and high seed protein content. Creation of high protein rice cultivars will greatly enhance our ability to meet the dietary needs of millions of malnourished people around the world.
Technical Abstract: Wild species offer a potential reservoir of genetic variation for crop improvement. Besides the valuable genes for disease resistance that the wild species have provided for rice improvement, recent studies have shown that these wild species could also provide favorable alleles for the improvement of yield and yield-related traits. In the present study, we report on yet another potential of wild relatives of rice which involve the improvement of seed protein content. A significant increase in seed protein content was observed in an interspecific hybrid between Oriza sativa ssp. indica, and the wild species Oryza nivara. The hybrid showed a protein content of 12.4%, which was 28% and 18.2% higher than the parents Oryza nivara and IR 64, respectively. The increase in protein content was dependent on the genetic background of the rice variety used in the hybridization. Sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis of seed storage proteins demonstrated a significant increase in prolamins and glutelins was mainly responsible for the elevated protein content of the hybrid. Amino acid analysis of seed proteins revealed that the hybrid had a net gain of 19.5% in lysine and 19.4% in threonine over the O. nivara parent on a seed dry weight basis. Molecular analysis indicated that the increase in protein content of the hybrid was not a result of chromosomal rearrangements or transposable element activation, at least in the chromosomal regions containing seed storage protein genes. A preliminary genetic analysis of F2 segregating population showed that the inheritance of the increased protein content was polygenic in nature. The development of this interspecific hybrid offers a great potential for selecting new rice cultivars that combine the high yield and superior cooking quality of IR 64 with improved seed protein content.