A Comparative Study of Selected Physical and Biochemical Traits of Wild-Type and Transgenic Sorghum to Reveal Differences Relevant to Grain Quality.

Transgenic sorghum featuring RNAi suppression of certain kafirins was developed recently, to address the problem of poor protein digestibility in the grain. However, it was not firmly established if other important quality parameters were adversely affected by this genetic intervention. In the present study several quality parameters were investigated by surveying several important physical and biochemical grain traits. Important differences in grain weight, density and endosperm texture were found that serve to differentiate the transgenic grains from their wild-type counterpart. In addition, ultrastructural analysis of the protein bodies revealed a changed morphology that is indicative of the effect of suppressed kafirins. Importantly, lysine was found to be significantly increased in one of the transgenic lines in comparison to wild-type; while no significant changes in anti-nutritional factors could be detected. The results have been insightful for demonstrating some of the corollary changes in transgenic sorghum grain, that emerge from imposed kafirin suppression.

Co-suppression of synthesis of major α-kafirin sub-class together with γ-kafirin-1 and γ-kafirin-2 required for substantially improved protein digestibility in transgenic sorghum.

KEY MESSAGE: Co-suppressing major kafirin sub-classes is fundamental to improved protein digestibility and nutritional value of sorghum. The improvement is linked to an irregularly invaginated phenotype of protein bodies. ABSTRACT: The combined suppression of only two genes, γ kafirin-1 (25 kDa) and γ-kafirin-2 (50 kDa), significantly increases sorghum kafirin in vitro digestibility. Co-suppression of a third gene, α-kafirin A1 (25 kDa), in addition to the two genes increases the digestibility further. The high-digestibility trait has previously only been obtained either through the co-suppression of six kafirin genes (α-A1, 25 kDa; α-B1, 19 kDa; α-B2, 22 kDa; γ-kaf1, 27 kDa; γ-kaf 2, 50 kDa; and δ-kaf 2, 18 kDa) or through random chemical-induced mutations (for example, the high protein digestibility mutant). We present further evidence that suppressing just three of these genes alters kafirin protein cross-linking and protein body microstructure to an irregularly invaginated phenotype. The irregular invaginations are consistent with high pepsin enzyme accessibility and hence high digestibility. The approach we adopted towards increasing sorghum protein digestibility appears to be an effective tool in improving the status of sorghum as a principal supplier of energy and protein in poor communities residing in marginal agro-ecological zones of Africa.

Induced protein polymorphisms and nutritional quality of gamma irradiation mutants of sorghum.

Physical and biochemical analysis of protein polymorphisms in seed storage proteins of a mutant population of sorghum revealed a mutant with redirected accumulation of kafirin proteins in the germ. The change in storage proteins was accompanied by an unusually high level accumulation of free lysine and other essential amino acids in the endosperm. This mutant further displayed a significant suppression in the synthesis and accumulation of the 27kDa γ-, 24kDa α-A1 and the 22kDa α-A2 kafirins in the endosperm. The suppression of kafirins was counteracted by an upsurge in the synthesis and accumulation of albumins, globulins and other proteins. The data collectively suggest that sorghum has huge genetic potential for nutritional biofortification and that induced mutations can be used as an effective tool in achieving premium nutrition in staple cereals.

An alternative strategy for sustainable pest resistance in genetically enhanced crops.

Bacillus thuringiensis (Bt) crystal protein genes encode insecticidal delta-endotoxins that are widely used for the development of insect-resistant crops. In this article, we describe an alternative transgenic strategy that has the potential to generate broader and more sustainable levels of resistance against insect pests. Our strategy involves engineering plants with a fusion protein combining the delta-endotoxin Cry1Ac with the galactose-binding domain of the nontoxic ricin B-chain (RB). This fusion, designated BtRB, provides the toxin with additional, binding domains, thus increasing the potential number of interactions at the molecular level in target insects. Transgenic rice and maize plants engineered to express the fusion protein were significantly more toxic in insect bioassays than those containing the Bt gene alone. They were also resistant to a wider range of insects, including important pests that are not normally susceptible to Bt toxins. The potential impact of fusion genes such as BtRB in terms of crop improvement, resistance sustainability, and biosafety is discussed.