Genetic engineering as a tool for modification of seed storage proteins and improvement of nutritional value of cereal grain

In recent years, genetic engineering has become an effective tool for the genetic improvement of cultivated plants including changes in the composition grain storage proteins of cereal crops that are the main source of nutrition for humans. The review describes the approaches used in these studies: the introduction of genetic constructs (i) providing the synthesis of proteins that are absent in recipient cultivars; (ii) inducing RNA-silencing of genes encoding proteins with low nutritional value, (iii) regulating the pool of amino acids in the endosperm. The studies are referred, which reported on the introduction of additional genes of high molecular weight glutenins ( 1Dx5, 1Ax1, 1Bx17, 1By18, 1Dy10 and others) into the genomes of different lines and cultivars of wheat. In these studies, the transgenic lines with increased dough strength and elasticity were obtained. In addition to the practical importance, these studies allow understanding the role of individual genes of high and low molecular weight glutenins in the formation of wheat flour quality traits. The examples of marker-free transgenic wheat lines expressing 1Dy10 and 1Bx14 genes, as well as transfer of high molecular weight glutenin genes into the genomes of other cereals (rye, corn, sorghum) are given. The possibilities of using the RNAi technology to obtain new information about the mechanisms of development of protein bodies, vitreous endosperm formation, and the role of different classes of prolamins and glutenins in the technological properties of flour and dough are discussed. The examples of the creation of transgenic maize with improved nutritional value via RNA-silencing of prolamin genes, transgenic sorghum with improved protein digestibility (obtained by silencing gene of the g-kafirin, the protein that forms outer layer of the protein bodies, resistant to pepsin digestion), transgenic wheat with suppression of gliadin synthesis, which flour has a low toxicity to humans with celiac disease, forced to comply gluten-free diet, are given. An example of natural RNA-silencing is given Partivularly, in the rice mutant with reduced level of glutelin, a deletion between the two coding sequences, one of which has an inverted orientation has been detected in the Lgc1 locus. The genetic engineering approaches to increase the lysine content are described, e.g. introduction of genes that enhance its synthesis, such as dihydrodipicolinate synthase (DHPS) insensitive to feedback inhibition and aspartate kinase; suppression of zlkr / sdh gene regulating its catabolism; introduction of genes that control the synthesis of proteins with high lysine content (histones and other lysine-rich proteins). The prospects of using genetic engineering methods to create varieties with improved nutritional value are associated with the use of marker-free technologies, increasing accuracy of insertion of genetic constructs, using the methods of genome editing by artificially engineered nucleases.