Toward Development of Nutritionally Enhanced Sorghum

Authors: KAUR, RAJVINDER - UC BERKELEY; WONG, JOSHUA - UC BERKELEY; SINGH, JASWINDER - UC BERKELEY; Pedersen, Jeffrey; LEMAUX, PEGGY - UC BERKELEY; BUCHANAN, BOB - UC BERKELEY

Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 8/24/2007
Publication Date: 9/17/2007
Citation: Kaur, R., Wong, J., Singh, J., Pedersen, J.F., Lemaux, P.G., Buchanan, B.B. 2007. Toward Development of Nutritionally Enhanced Sorghum. Meeting Abstract.

Interpretive Summary: Grain sorghum is the fifth most important cereal crop worldwide. Sorghum is used primarily as animal feed in the developed world but, particularly in semi-arid regions of Africa and Asia, it serves as a principal source of energy and protein for millions of the poorest people. While having greater tolerance than maize to stresses like low water availability, sorghum has undesirable nutritional qualities that hinder its wider use. Two key properties leading to its poor nutritional quality are an amino acid imbalance (sorghum is low in tryptophan and lysine) and the relative indigestibility of its protein and starch by humans and non-ruminant animals such as poultry and swine. Amino acid deficiency is being addressed in several ways, including introduction of a gene for a lysine-rich barley hordothionin, HT12, targeted to the endosperm using a barley, seed-specific promoter and signal sequence. To determine the basis for the indigestibility of sorghum starch and protein relative to other cereals, the HT-12 lines and two U.S. lines derived from crosses of the same parents —the more digestible KS48 and the less digestible KS51—were also studied. Elevated expression of HT-12 in 296B had no apparent effect on digestibility of either starch or protein in sorghum grains. Based on a comparative analysis of KS51 and KS48, factors accounting for the poor digestibility of the starch and protein storage components in KS51 included: (i) a greater abundance of disulfide protein linkages that impede enzymes that digest the grain; (ii) presence of non-waxy starch and the accompanying granule-bound starch synthase; and (iii) differences in the nature of the starch/protein matrix. These features are important, not only for use of sorghum as food and feed, but also for potential application as a biofuel source and should be considered in efforts to improve sorghum grain for these different purposes.

Technical Abstract: Grain sorghum (Sorghum bicolor L. Moench) is the fifth most important cereal crop worldwide. Sorghum is used primarily as animal feed in the developed world but, particularly in semi-arid regions of Africa and Asia, it serves as a principal source of energy and protein for millions of the poorest people. While having greater tolerance than maize to abiotic stresses, like low water availability, sorghum has undesirable nutritional qualities that hinder its wider use. Two key properties leading to its poor nutritional quality are an amino acid imbalance (sorghum is particularly low in tryptophan and lysine) and the relative indigestibility of its protein and starch by humans and monogastric animals. Amino acid deficiency is being addressed in several ways, including introduction of a gene for a lysine-rich barley hordothionin, HT12, targeted to the endosperm using a barley, seed-specific promoter and signal sequence. Western blots of T2 seeds revealed a 7-fold difference in overexpression of HT12 among four independently transformed events of the Indian inbred line, 296B. To determine the basis for the indigestibility of sorghum starch and protein relative to other cereals, the HT-12 lines and two U.S. varieties derived from crosses of the same parents —the more digestible KS48 and the less digestible KS51—were also studied. Elevated expression of HT-12 in 296B had no apparent effect on digestibility of either starch or protein in sorghum grains. Based on a comparative analysis of KS51 and KS48, factors accounting for the poor digestibility of the starch and protein storage components in KS51 included: (i) a greater abundance of disulfide protein linkages that impede access to proteolytic and amylolytic enzymes; (ii) presence of non-waxy starch and the accompanying granule-bound starch synthase; and (iii) differences in the nature of the starch/protein matrix. These features are important, not only for use of sorghum as food and feed, but also for potential application as a biofuel source and should be considered in efforts to improve sorghum grain for these different purposes.