Abstract
Sorghum is one of the most important cereal crops in drought regions of the Globe. However, a number of constrains, such as poor nutritional value compared to other cereals, which is caused by resistance of its grain storage proteins (kafirins) to protease digestion, makes it less popular. The use of modern genetic technologies, such as RNA interference, opens up prospects for solving this problem. In this paper, we describe the inheritance of the genetic construct for RNAi silencing of the γ-kafirin gene (gKAF1) in the progeny of the mutant Avans-1/18, that we obtained previously by Agrobacterium-mediated genetic transformation of immature embryos of commercial cv. Avans. Inheritance of the genetic construct was traced by PCR-analysis to the nos-promoter governing expression of the marker gene bar and to the ubi1-intron, which is part of the genetic construct for silencing. It was found that the genetic construct inherited in T1and T2generations of the mutant grown both in the growth chamber and in the field plot, and in the F1hybrids of the mutant with CMS-lines A2 KVV-181, A2 KVV-114, A2 O-1237, and fertile lines Volzhskoe-4v, Volzhskoe-615, O-1237. The studied plants from T1and T2generations had significantly higher in vitro protein digestibility than original non-transgenic cv. Avans. The vitreous endosperm in these plants was reduced either completely or manifested a faint layer. These data demonstrated that genetic construct for gKAF1 silencing was not only stably integrated in genome of the mutant plants but also expressed and improved the digestibility of endosperm proteins. In addition, in T1 progeny we found the plant, PCR positive for nos-promoter but PCR-negative for ubi1-intron, that had vitreous endosperm and was characterized by poor in vitro protein digestibility. These data are an example of instability of the genetic construct for RNAi-silencing in genome of some transgenic plants; they show close correlation of the floury endosperm type and high in vitro protein digestibility.
Highlights
One of the most important areas of plant biotechnology is improving the nutritional properties of food and feed crops
It is believed that γ-kafirin plays an important role in the poor digestibility of kafirins by proteases [5] because it is abundant in cysteine capable to form intra- and intermolecular S-S bonds that results in formation of kafirin oligo- and polymers resistant to protease digestion
Published reports indicate that this approach allows the creation of sorghum lines with a reduced content of kafirins, which leads to improved digestibility of endosperm proteins by proteases and the synthesis of other proteins with higher content of essential amino acids [9,10,11,12]
Summary
One of the most important areas of plant biotechnology is improving the nutritional properties of food and feed crops. Nutritional as well as forage value of sorghum grain are significantly restricted because of resistance of its storage proteins – kafirins – to protease digestion [1,2,3,4]. Peripheral disposition of γ-kafirin within the protein bodies prevents protease digestion of the main sorghum storage proteins – α-kafirins. Another factor determining poor nutritional value of sorghum grain is the deficiency of essential amino acids, primarily, lysine, that is caused by its low content in the kafirins [68]
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