Improving the protein content and composition of cereal grain

Pathways regulating threonine, methionine and isoleucine metabolism are very efficiently interconnected in plants. As both threonine and methionine serve as substrates for isoleucine synthesis, their synthesis and catabolism under different developmental and environmental conditions also influence isoleucine availability. Together, methionine gamma-lyase and threonine deaminase maintain the isoleucine equilibrium in plants under varied substrate availabilities. Isoleucine and the two other branched-chain amino acids (BCAAs) (leucine and valine) share four common enzymes in their biosynthesis pathways and thus are coordinately regulated. Induction of free amino acids as osmolytes in response to abiotic stress is thought to play a role in plant stress tolerance. In particular, the accumulation of BCAAs is induced many-fold during osmotic stress. However, unlike in the case of proline, not much research has been focused on understanding the function of the response involving BCAAs. This review describes pathways influencing branched-chain amino acid metabolism and what is known about the biological significance of their accumulation under abiotic stress. A bioinformatics approach to understanding the transcriptional regulation of the genes involved in amino acid metabolism under abiotic stress is also presented.

Interdependence of threonine, methionine and isoleucine metabolism in plants: accumulation and transcriptional regulation under abiotic stress.

The inability of humans and many farm animals to synthesize certain amino acids has long triggered tremendous interest in increasing the levels of these so-called essential amino acids in crop plants. Knowledge obtained from basic genetic and genetic engineering research has also been successfully

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Improving the content of essential amino acids in crop plants: goals and opportunities.

Crop nitrogen requirements, utilization, and fertilization.

1 Introduction- 2 Methods for Inducing Mutations- 21 Mutagenic Agents and Related Problems- 22 The Chimerical Structure of the M1 Plants- 3 The Selection Value of Mutant Genes- 4 The Seed Production of Mutants and the Alteration of Quantitative Characters- 41 The Alteration of Quantitative Characters- 42 Mutants with Increased Seed Yield- 43 Released or Approved Mutant Varieties- 5 The Utilization of Mutants in Crossbreeding- 51 The Incorporation of Mutant Genes into the Genomes of Varieties or Strains- 52 The Joint Action of Mutant Genes- 521 Negative Interactions- 522 Positive Interactions- 6 The Alteration of the Shoot System by Means of Mutations- 61 Mutants with Reduced Plant Height: Erectoides Types, Semidwarfs, Dwarfs- 611 Barley- 612 Rice- 613 Bread and Durum Wheat Other Gramineae- 614 Dicotyledonous Crops- 62 Mutants with Increased Plant Height- 63 Mutants with Altered Stem Structure- 631 Branching, Tillering- 632 Stem Bifurcation- 6321 Bifurcated Mutants- 6322 Bifurcated Recombinants- 633 Stem Fasciation- 6331 Fasciated Mutants- 6332 Fasciated Recombinants- 634 Mutations in Fiber Plants- 7 Alterations of Flower Shape, Color and Function- 71 Flower Shapes and Flower Colors in Ornamentals- 72 Inflorescences- 73 Genetic Male Sterility- 8 Leaf Mutants of Agronomic Interest- 9 Mutations Affecting the Root System- 10 The Alteration of Flowering and Ripening Times- 101 Earliness- 102 Lateness- 103 Changes of the Photoperiodic Reaction- 11 Mutations in Vegetatively Propagated Crops and Ornamentals- 12 Heterosis- 13 Disease Resistance- 131 Resistance Against Fungi, Bacteria, and Viruses- 1311 Barley- 1312 Rice- 1313 Bread and Durum Wheat- 1314 Oats- 1315 Maize- 1316 Pearl Millet- 1317 Sugarcane- 1318 Dicotyledonous Crops- 132 Resistance Against Animal Pathogens- 133 Herbicide Tolerance- 14 Drought Resistance, Heat Tolerance, Winterhardiness- 15 Shattering and Shedding Resistance- 16 The Pleiotropic Gene Action as a Negative Factor in Mutation Breeding- 161 The Alteration of Pleiotropic Patterns Under the Influence of Changed Genotypic Background or Environment- 162 Mutations of Closely Linked Genes- 17 The Penetrante Behavior of Mutant Genes as a Negative Factor- 18 The Adaptability of Mutants to Altered Environmental Conditions- 181 The Reaction of Mutants to Different Natural Environments- 182 The Reaction of Mutants Under Controlled Phytotron Conditions- 19 The Alteration of Morphological and Physiological Seed Characters- 191 Seed Size- 192 Seed Shape- 193 Seed Color- 194 Physiological Seed Characters- 20 The Alteration of Seed Storage Substances- 201 Seed Proteins- 2011 The Characterization of Seed Proteins- 2012 Factors Influencing Protein Content and Composition- 20121 Environmental Factors- 20122 Endogenous Factors- 2013 Seed Protein Content of Different Varieties of the Same Species- 2014 Alteration of Seed Proteins Through Mutant Genes- 20141 Protein Mutants in Cereals- 20142 Protein Mutants in Legumes- 202 Seed Carbohydrates- 2021 Maize- 2022 Barley and Other Cereals- 2023 Peas- 203 Seed Lipids- 21 Other Plant Substances- 22 The Nutritional Value of Mutants- 221 Maize Mutants- 222 Barley Mutants- 223 Sorghum Genotypes- 224 Pea Mutants- 23 General Aspects of Mutation Breeding with Regard to the Improvement of Seed Storage Substances- References

Induced Mutations in Plant Breeding

Seeds from over 9,000 lines in the world sorghum [Sorghum bicolor (L.) Moench] collection were classified for endosperm phenotype to identify floury endosperm lines and evaluate each for potential increases in lysine concentration. Sixty-two floury endosperm lines were selected and analyzed for protein and lysine composition. Two floury lines of Ethiopian origin, IS 11167 and IS 11758, were exceptionally high in lysine at relatively high levels of protein.

The average whole grain lysine concentration of high lysine lines IS 11167 and IS 11758 was 3.34 and 3.13 (g/lOOg protein) at 15.7 and 17.2% protein, respectively. Both lines were also high in percent oil. Carbohydrate analyses of whole grain samples of the two high lysine lines were similar to that of normal sorghum grain except for a twofold increase in sucrose concentration.

The high lysine gene altered the amino acid pattern in hl hl hl endosperm tissue relative to normal endosperm checks. The major changes were increased lysine, arginine, aspartic acid, glycine, and tryptophan concentrations and decreased amounts of glutamic acid, proline, alanine, and leucine in the hl hl hl endosperm.

Inheritance studies suggest that the increased lysine concentration of each line is controlled by a single recessive gene, although it is not known whether the genes from both lines are allelic. The high lysine gene(s) present in IS 11167 and IS 11758 from Ethiopia is (are) herein designated as hl. The endosperm of kernels homozygous for the hl gene is partially dented.

The biological value of the high lysine lines was much higher than that of average sorghum lines. In a 28-day isonitrogenous feeding experiment the weight gain of weanling rats was three times higher on an IS 11758 ration and twice as high on an IS 11167 ration as weight gains on rations prepared from normal sorghum lines. When fed rations without any dilution except the usual 2% vitamin and 4% mineral supplementation, rats gained 94 g on high lysine sorghum (IS 11758) and 28.5 g on our current best nutritional quality sorghum line (IS 2319), versus 91.5 g on opaque-2 corn (Zea mays L.) and 30.2 g on normal corn in a 28-day feeding trial. Feed efficiency ratios for this trial were 3.0 for high lysine sorghum, 6.8 for IS 2319, 3.4 for opaque-2 corn, and 7.4 for normal corn.

Rameshwar Singh

Papers

High Lysine Mutant Gene (hl that Improves Protein Quality and Biological Value of Grain Sorghum1