Please cite this article in press as: L. Mehlo, et al., Induced protein polymorphisms and nutritional quality of gamma irradiation mutants of sorghum, Mutat. Res.: Fundam. Mol. Mech. Mutagen. (2013), http://dx.doi.org/10.1016/j.mrfmmm.2013.05.002 ARTICLE IN PRESS G Model MUT-11272; No. of Pages 7 Mutation Research xxx (2013) xxx–xxx Contents lists available at SciVerse ScienceDirect Mutation Research/Fundamental and Molecular Mechanisms of Mutagenesis jo ur nal ho me p a ge: www.elsevier.com/locate/molmut C om mu n i ty add ress: www.elsevier.com/locate/mutres Induced protein polymorphisms and nutritional quality of gamma irradiation mutants of sorghum  Luke Mehlo a,∗ , Zodwa Mbambo a,c , Souleymane Bado b , Johnson Lin c , Sydwell M. Moagi a , Sindisiwe Buthelezi a , Stoyan Stoychev a , Rachel Chikwamba a a CSIR Biosciences, Meiring Naude Road, P.O. Box 395, Pretoria 0001, South Africa b Plant Breeding and Genetics Laboratory – Joint FAO/IAEA Agriculture and Biotechnology Laboratory, International Atomic Energy Agency Laboratories, A-2444 Seibersdorf, Austria c Microbiology Discipline, School of Life Sciences, University of KwaZulu-Natal (Westville Campus), Private Bag X54001, Durban 4000, South Africa a r t i c l e i n f o Article history: Received 25 March 2013 Received in revised form 2 May 2013 Accepted 14 May 2013 Available online xxx Keywords: Induced mutations Nutritional quality Gamma irradiation Amino acid Sorghum a b s t r a c t Physical and biochemical analysis of protein polymorphisms in seed storage proteins of a mutant popu- lation 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 27 kDa -, 24 kDa -A1 and the 22 kDa -A2 kafirins in the endosperm. The suppression of kafirins was counteracted by an upsurge in the synthesis and accumu- lation 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. © 2013 Published by Elsevier B.V. 1. Introduction Seed storage proteins of major cereal grains like wheat, maize, barley, rice and sorghum are a cornerstone of nutrition. Global estimates suggest that these cereals generally supply between 50 and 70% of dietary proteins and calorific intakes for humans [1]. Worse still for approximately one third of the world’s population in resource-poor countries of Sub Saharan Africa and South East Asia, one cereal crop is usually the only main source of nutrition [2]. Current changes in climate and its impact on global cereal crop production, notably the increased incidences of drought and crop failure, therefore refocus attention to the cultivation of adaptable cereal crops like sorghum [3–5]. In the future, the number of peo- ple consuming sorghum is therefore likely to increase, especially in the semi-arid regions of the world where other cereals like rice, wheat and barley have limited adaptability [6]. Even though there are models predicting that population growth may significantly slow down at some stage, the global population is at least expected  This is an open-access article distributed under the terms of the Creative Com- mons Attribution-NonCommercial-No Derivative Works License, which permits non-commercial use, distribution, and reproduction in any medium, provided the original author and source are credited. ∗ Corresponding author. Tel.: +27 12 8412535. E-mail address: LMehlo@csir.co.za (L. Mehlo). to grow from the current 7 billion to 9.3 billion people in 2050 and to 10.1 billion people in 2100, thus suggesting a need to increase agricultural production and the nutritional quality of food [7]. Unfortunately, a staple diet consisting of sorghum is likely to lead to malnutrition. Sorghums’ seed storage proteins do not provide a balanced source of protein and calories. The predomi- nant storage proteins in sorghum seeds (prolamins) are deficient in many essential amino acids like lysine, methionine and tryptophan. Sorghum storage proteins are also less digestible by proteases and are even more so upon cooking [5]. There are many reasons for the poor digestibility of sorghum proteins. These include the chemical structure of kafirin molecules; for example, the - and -kafirins have abundant sulphur-containing amino acids capable of forming strong protease digestion-resistant S S bonds. Also, the interac- tion of kafirins with non-protein molecules like polyphenols and polysaccharides interfere with digestion. The spatial organisation of different kafirins within protein bodies additionally ensures that the more digestible and most abundant -kafirins are shielded in the centre of protein bodies by less digestible - and -kafirins [6,8]. The sorghum grain is also deficient in vitamin A, and its con- tent of iron and zinc has limited bioavailability. This is because the two microelements are bound by phytate [1,9]. Research has however shown that the nutritive value of sorghum can be improved [9,10]. A reduction in the synthesis of - and -kafirins through genetic engineering with RNA interfer- ence constructs containing hairpins of the two kafirin species can 0027-5107/$ – see front matter © 2013 Published by Elsevier B.V. http://dx.doi.org/10.1016/j.mrfmmm.2013.05.002