Characterization of the maize Globulin-2 gene and analysis of two null alleles

Accumulation Profiles of Embryonic Salt-Soluble Proteins in Maize Hybrids and Parental Lines Indicate Matroclinous Inheritance: A Proteomic Analysis

Maize is one of the most widely cultivated crops. It accumulates a large quantity of seed storage proteins, which are important for seed development and germination, and contribute to the nutritional quality of seeds. Based on solubility, the storage proteins are divided into albumins (water-soluble), globulins (salt-soluble), prolamins (alcohol-soluble), and glutelins (acid- or alkali-soluble). Maize hybrids are cultivated due to the superior performance of F₁ hybrids than that of their parents, a phenomenon known as heterosis. However, the accumulation patterns of seed storage proteins in maize embryos between the hybrids and their parental inbred lines have not been compared. In the present study, two elite inbred lines of China, Zheng 58 and Chang 7-2, and their reciprocal hybrids (Zheng 58 × Chang 7-2 and Chang 7-2 × Zheng 58) were used to explore parental influences on the accumulation patterns of seed storage proteins in maize embryos. For this purpose, we focused on seed salt-soluble proteins (SSPs) in our experiments. The SSPs were selectively extracted from maize mature embryos after extensive removal of water-soluble albumin and separated using two-dimensional gel electrophoresis (2-DE), followed by mass spectrometry analysis. Our results indicated that the 2-DE SSP profiles of hybrids closely resembled those of their maternal parent rather than the paternal parent. In other words, 2-DE SSP profiles of Zheng 58 × Chang 7-2 were more similar those of Zheng 58 whereas such profiles of Chang 7-2 × Zheng 58 were more similar to those of Chang 7-2 although the 2-DE profiles of all four maize types were quite similar. In total, 12 relatively abundant SSPs spots representing five kinds of proteins were identified, of which nine protein spots displayed non-additive accumulation in at least one hybrid. This study provided additional data on dominance and partial dominance effects on maize hybrids embryos. Besides, earlier studies on accumulation profiles of globulin-1 (also known as vicilin), which is one of the most abundant globulins in maize embryos, also support the above results. This study would be helpful in revealing the mechanisms underlying SSPs accumulation patterns in the hybrids.

Grain sorghum proteomics: integrated approach toward characterization of endosperm storage proteins in kafirin allelic variants

Grain protein composition determines quality traits, such as value for food, feedstock, and biomaterials uses. The major storage proteins in sorghum are the prolamins, known as kafirins. Located primarily on the periphery of the protein bodies surrounding starch, cysteine-rich β- and γ-kafirins may limit enzymatic access to internally positioned α-kafirins and starch. An integrated approach was used to characterize sorghum with allelic variation at the kafirin loci to determine the effects of this genetic diversity on protein expression. Reversed-phase high performance liquid chromatography and lab-on-a-chip analysis showed reductions in alcohol-soluble protein in β-kafirin null lines. Gel-based separation and liquid chromatography-tandem mass spectrometry identified a range of redox active proteins affecting storage protein biochemistry. Thioredoxin, involved in the processing of proteins at germination, has reported impacts on grain digestibility and was differentially expressed across genotypes. Thus, redox states of endosperm proteins, of which kafirins are a subset, could affect quality traits in addition to the expression of proteins.

Analogous reserve distribution and tissue characteristics in quinoa and grass seeds suggest convergent evolution

Quinoa seeds are highly nutritious due to the quality of their proteins and lipids and the wide range of minerals and vitamins they store. Three compartments can be distinguished within the mature seed: embryo, endosperm, and perisperm. The distribution of main storage reserves is clearly different in those areas: the embryo and endosperm store proteins, lipids, and minerals, and the perisperm stores starch. Tissues equivalent (but not homologous) to those found in grasses can be identified in quinoa, suggesting the effectiveness of this seed reserve distribution strategy; as in cells of grass starchy endosperm, the cells of the quinoa perisperm endoreduplicate, increase in size, synthesize starch, and die during development. In addition, both systems present an extra-embryonic tissue that stores proteins, lipids and minerals: in gramineae, the aleurone layer(s) of the endosperm; in quinoa, the micropylar endosperm; in both cases, the tissues are living. Moreover, the quinoa micropylar endosperm and the coleorhiza in grasses play similar roles, protecting the root in the quiescent seed and controlling dormancy during germination. This investigation is just the beginning of a broader and comparative study of the development of quinoa and grass seeds. Several questions arise from this study, such as: how are synthesis and activation of seed proteins and enzymes regulated during development and germination, what are the genes involved in these processes, and lastly, what is the genetic foundation justifying the analogy to grasses.

Mutational breeding and genetic engineering in the development of high grain protein content

Cereals are the most important crops in the world for both human consumption and animal feed. Improving their nutritional values, such as high protein content, will have significant implications, from establishing healthy lifestyles to helping remediate malnutrition problems worldwide. Besides providing a source of carbohydrate, grain is also a natural source of dietary fiber, vitamins, minerals, specific oils, and other disease-fighting phytocompounds. Even though cereal grains contain relatively little protein compared to legume seeds, they provide protein for the nutrition of humans and livestock that is about 3 times that of legumes. Most cereal seeds lack a few essential amino acids; therefore, they have imbalanced amino acid profiles. Lysine (Lys), threonine (Thr), methionine (Met), and tryptophan (Trp) are among the most critical and are a limiting factor in many grain crops for human nutrition. Tremendous research has been put into the efforts to improve these essential amino acids. Development of high protein content can be outlined in four different approaches through manipulating seed protein bodies, modulating certain biosynthetic pathways to overproduce essential and limiting amino acids, increasing nitrogen relocation to the grain through the introduction of transgenes, and exploiting new genetic variance. Various technologies have been employed to improve protein content including conventional and mutational breeding, genetic engineering, marker-assisted selection, and genomic analysis. Each approach involves a combination of these technologies. Advancements in nutrigenomics and nutrigenetics continue to improve public knowledge at a rapid pace on the importance of specific aspects of food nutrition for optimum fitness and health. An understanding of the molecular basis for human health and genetic predisposition to certain diseases through human genomes enables individuals to personalize their nutritional requirements. It is critically important, therefore, to improve grain protein quality. Highly nutritious grain can be tailored to functional foods to meet the needs for both specific individuals and human populations as a whole.

Proteomics study of rice embryogenesis: discovery of the embryogenesis-dependent globulins

The plant embryo is the germination center of the seed. How an embryo forms during seed maturation remains unclear, especially in the case of monocotyledonous plants. Generally, the complex processes of embryogenesis result from the action of a coordinated network of genes. Thus, a large-scale survey of changes in protein abundance during embryogenesis is an effective approach to study the molecular events of embryogenesis. In this study, two-dimensional gel electrophoresis (2DE) was applied to separate rice embryo proteins collected during the three phases of embryogenesis: 6 days after pollination (DAP), 12 DAP, and 18 DAP. We then employed matrix-assisted laser desorption-ionization time of flight/time of flight mass spectrometry(MALDI TOF/TOF MS) to identify the phase-dependent differential 2DE spots. A total of 66 spots were discovered to be regulated during embryogenesis, and of these spots, 53 spots were identified. These proteins were further categorized into several functional classes, including storage, embryo development, stress response, glycolysis, and protein metabolism. Intriguingly, the major differential spots originated from three globulins. We further examined the possible mechanism underlying the globulins' multiple forms using Western blotting, proteolysis, and blue native gel electrophoresis techniques and found that the multiple forms of globulins were produced as a result of enhanced proteolysis during embryogenesis, indicating that these globulin forms may serve as chaperone proteins participating in the formation of multiple protein complexes during embryogenesis.

Cereal seed storage proteins: structures, properties and role in grain utilization

Storage proteins account for about 50% of the total protein in mature cereal grains and have important impacts on their nutritional quality for humans and livestock and on their functional properties in food processing. Current knowledge of the structures and properties of the prolamin and globulin storage proteins of cereals and their mechanisms of synthesis, trafficking and deposition in the developing grain is briefly reviewed here. The role of the gluten proteins of wheat in determining the quality of the grain for breadmaking and how their amount and composition can be manipulated leading to changes in dough mixing properties is also discussed.

Comparison of constitutive and inducible maize kernel proteins of genotypes resistant or susceptible to aflatoxin production

Maize genotypes resistant or susceptible to aflatoxin production or contamination were compared for differences in both constitutive and inducible proteins. Five additional constitutive proteins were found to be associated with resistance in over 8 of the 10 genotypes examined. Among these, the 58- and 46-kDa proteins were identified as globulin-1 and globulin-2, respectively. Differences in the ability to induce specific antifungal proteins, such as the higher synthesis of the 22-kDa zeamatin in resistant genotypes, were also observed between resistant and susceptible kernels incubated under germinating conditions (31 degrees C, 100% humidity). Both constitutive and inducible proteins appear to be necessary for kernel resistance. Embryo-killed kernels (unable to synthesize new proteins) supported the highest level of aflatoxins, whereas imbibed kernels (to hasten protein induction) supported the lowest among all treatments. This suggests that the synthesis of new proteins by the embryo plays an important role in conferring resistance. However, significantly lower levels of aflatoxin production in embryo-killed resistant kernels than in susceptible ones suggest that, in reality, high levels of constitutive antifungal proteins are indispensable to kernel resistance.

Tissue-specific and ABA-regulated Maize GIN gene expression in transgenic tobacco

To study the regulatory functions of the ON promoter region, a ppG1b1GUS construct, consisting of 1402 bp 5' flanking sequence ofGlbl, 1919 by GUS coding sequence, and 283 by 3' NOS terminator, was cloned into a binary vector and introduced into tobacco plants byAgrobacterium-mediated transformation. Histochemical GUS assays of To tobacco mature seeds indicate that theGlbl promoter drives GUS expression in ABA treated seeds. Further GUS assays of the T, seeds at different developmental stages revealed that without ABA treatment, theGibl promoter drives GUS expression in immature seeds. The results from both To and T1 tobacco plants indicated thatGlbl-driven GUS expression in tobacco is embryo specific.

Barley embryo globulin 1 gene, Beg1: characterization of cDNA, chromosome mapping and regulation of expression

We report identification of a 2189 bp cDNA clone from barley corresponding to a single-copy gene, Beg1 (Barley embryo globulin), on chromosome 4, which encodes a storage globulin. In barley, the major protein reserve in the aleurone layer belongs to the 7S globulin class of proteins found in many seeds. Electrophoretically and antigenically similar proteins are present in the barley embryo. Accumulation of Beg1 mRNA was noted beginning 15-20 days post-anthesis in both the aleurone layer and embryo of the developing barley grain but not in the starchy endosperm. A high level of Beg1 mRNA is also present in the mature imbibed aleurones, which can be repressed by treatment with gibberellic acid. This repressive effect of gibberellin on the levels of Beg1 mRNA is confirmed in the gibberellin response-constitutive mutant, slender, whose aleurone layers do not accumulate Beg1 mRNA even in the absence of applied gibberellic acid. The deduced primary translation product of the Beg1 mRNA is a 63.7 amino acid (72 kDa) protein with homology to maize embryo globulin 1 (GLB1) and a partial sequence of a wheat 7S globulin. The internal amino acid sequence of BEG1 closely matches the N-terminal sequence of isolated barley aleurone globulin. Seven imperfect tandem repeats of 16 amino acids each are present near the N-terminus of BEG1, which conform to the consensus HGEGEREEEXGRGRGR, and contribute to the observed unusual amino acid composition of this protein. A second, distinct barley globulin gene, Beg2, which is homologous to maize Glb2, was detected by Northern and Southern analysis. Beg2 and Beg1 are regulated differently which may indicate variation in storage or utilization properties among the barley globulins.