Identification and characterization of DNA clones encoding group-II glycinin subunits

Soybean genetics, genomics, and breeding for improving nutritional value and reducing antinutritional traits in food and feed

Soybean [Glycine max (L.) Merr.] is a globally important crop due to its valuable seed composition, versatile feed, food, and industrial end-uses, and consistent genetic gain. Successful genetic gain in soybean has led to widespread adaptation and increased value for producers, processors, and consumers. Specific focus on the nutritional quality of soybean seed composition for food and feed has further elucidated genetic knowledge and bolstered breeding progress. Seed components are historical and current targets for soybean breeders seeking to improve nutritional quality of soybean. This article reviews genetic and genomic foundations for improvement of nutritionally important traits, such as protein and amino acids, oil and fatty acids, carbohydrates, and specific food-grade considerations; discusses the application of advanced breeding technology such as CRISPR/Cas9 in creating seed composition variations; and provides future directions and breeding recommendations regarding soybean seed composition traits.

Genetic mapping and functional genomics of soybean seed protein

Soybean is an utterly important crop for high-quality meal protein and vegetative oil. Soybean seed protein content has become a key factor in nutrients for livestock feed as well as human dietary consumption. Genetic improvement of soybean seed protein is highly desired to meet the demands of rapidly growing world population. Molecular mapping and genomic analysis in soybean have identified many quantitative trait loci (QTL) underlying seed protein content control. Exploring the mechanisms of seed storage protein regulation will be helpful to achieve the improvement of protein content. However, the practice of breeding higher protein soybean is challenging because soybean seed protein is negatively correlated with seed oil content and yield. To overcome the limitation of such inverse relationship, deeper insights into the property and genetic control of seed protein are required. Recent advances of soybean genomics have strongly enhanced the understandings for molecular mechanisms of soybean with better seed quality. Here, we review the research progress in the genetic characteristics of soybean storage protein, and up-to-date advances of molecular mappings and genomics of soybean protein. The key factors underlying the mechanisms of the negative correlation between protein and oil in soybean seeds are elaborated. We also briefly discuss the future prospects of breaking the bottleneck of the negative correlation to develop high protein soybean without penalty of oil and yield.

Supplementary Information

The online version contains supplementary material available at 10.1007/s11032-023-01373-5.

Soybean genetic resources contributing to sustainable protein production

KEY MESSAGE

Genetic resources contributes to the sustainable protein production in soybean. Soybean is an important crop for food, oil, and forage and is the main source of edible vegetable oil and vegetable protein. It plays an important role in maintaining balanced dietary nutrients for human health. The soybean protein content is a quantitative trait mainly controlled by gene additive effects and is usually negatively correlated with agronomic traits such as the oil content and yield. The selection of soybean varieties with high protein content and high yield to secure sustainable protein production is one of the difficulties in soybean breeding. The abundant genetic variation of soybean germplasm resources is the basis for overcoming the obstacles in breeding for soybean varieties with high yield and high protein content. Soybean has been cultivated for more than 5000 years and has spread from China to other parts of the world. The rich genetic resources play an important role in promoting the sustainable production of soybean protein worldwide. In this paper, the origin and spread of soybean and the current status of soybean production are reviewed; the genetic characteristics of soybean protein and the distribution of resources are expounded based on phenotypes; the discovery of soybean seed protein-related genes as well as transcriptomic, metabolomic, and proteomic studies in soybean are elaborated; the creation and utilization of high-protein germplasm resources are introduced; and the prospect of high-protein soybean breeding is described.

Linkage and association study discovered loci and candidate genes for glycinin and β-conglycinin in soybean (Glycine max L. Merr.)

KEY MESSAGE

Linkage mapping and GWAS identified 67 QTLs related to soybean glycinin, β-conglycinin and relevant traits. Polymorphisms of the candidate gene Gy1 promoter were associated with the glycinin content in soybean. The major components of storage proteins in soybean seeds are glycinin and β-conglycinin, which play important roles in determining protein nutrition and soy food processing properties. Increasing the protein content while improving the ratio of glycinin to β-conglycinin is substantially important for soybean protein improvement. To investigate the genetic mechanism of storage protein subunits, 184 recombinant inbred lines (RILs) derived from a cross of Kefeng No. 1 and Nannong 1138-2 and 211 diverse soybean cultivars were used to detect loci related to glycinin (11S), β-conglycinin (7S), the sum of glycinin and β-conglycinin (SGC), and the ratio of glycinin to β-conglycinin (RGC). Sixty-seven QTLs and 11 hot genomic regions were identified as affecting the four traits. One genetic region (q10-1) on chromosome 10 was associated with multiple traits by both linkage and association analysis. Eight genes in 11 hot genomic regions might be related to soybean protein subunit. The candidate gene analysis showed that polymorphisms in Gy1 promoters were significantly correlated with the 11S content. The QTLs and candidate genes identified in the present study allow for further understanding the genetic basis of 11S and 7S regulation and provide useful information for marker-assisted selection (MAS) in soybean quality improvement.

A space-saving visual screening method, Glycine max FAST, for generating transgenic soybean

Establishing homozygous transgenic lines of Glycine max is time-consuming and laborious. To overcome the difficulties, we developed a powerful method for selecting transgenic soybean plants, Fluorescence-Accumulating Seed Technology (GmFAST). GmFAST uses a marker composed of a soybean seed-specific promoter coupled to the OLE1-GFP gene, which encodes a GFP fusion of the oil-body membrane protein OLEOSIN1 of Arabidopsis thaliana. We introduced the marker gene into cotyledonary nodes of G. max Kariyutaka via Agrobacterium-mediated transformation and regenerated heterozygous transgenic plants. OLE1-GFP-expressing soybean seeds can be selected nondestructively with a fluorescence stereomicroscope. Among T2 seeds, the most strongly fluorescent seeds were homozygous. GmFAST enables to reduce the growing space by one-tenth compared with the conventional method. With this method, we obtained the soybean line that had higher levels of seed pods and oil production. The phenotypes are presumably caused by overexpression of Glyma13g30950, suggesting that Glyma13g30950 regulates seed pod formation in soybean plants. An increase in seed pod number was confirmed in A. thaliana plants that overexpressed the Arabidopsis ortholog of Glyma13g30950, E6L1.Taken together, GmFAST provides a space-saving visual and nondestructive screening method for soybean transformation, thereby increasing the chance of developing useful soybean lines.

Genetic mapping and validation of the loci controlling 7S α' and 11S A-type storage protein subunits in soybean [Glycine max (L.) Merr.]

KEY MESSAGE

Four soybean storage protein subunit QTLs were mapped using bulked segregant analysis and an F2 population, which were validated with an F5 RIL population. The storage protein globulins β-conglycinin (7S subunit) and glycinin (11S subunits) can affect the quantity and quality of proteins found in soybean seeds and account for more than 70% of the total soybean protein. Manipulating the storage protein subunits to enhance soymeal nutrition and for desirable tofu manufacturing characteristics are two end-use quality goals in soybean breeding programs. To aid in developing soybean cultivars with desired seed composition, an F2 mapping population (n = 448) and an F5 RIL population (n = 180) were developed by crossing high protein cultivar 'Harovinton' with the breeding line SQ97-0263_3-1a, which lacks the 7S α', 11S A1, 11S A2, 11S A3 and 11S A4 subunits. The storage protein composition of each individual in the F2 and F5 populations were profiled using SDS-PAGE. Based on the presence/absence of the subunits, genomic DNA bulks were formed among the F2 plants to identify genomic regions controlling the 7S α' and 11S protein subunits. By utilizing polymorphic SNPs between the bulks characterized with Illumina SoySNP50K iSelect BeadChips at targeted genomic regions, KASP assays were designed and used to map QTLs causing the loss of the subunits. Soybean storage protein QTLs were identified on Chromosome 3 (11S A1), Chromosome 10 (7S α' and 11S A4), and Chromosome 13 (11S A3), which were also validated in the F5 RIL population. The results of this research could allow for the deployment of marker-assisted selection for desired storage protein subunits by screening breeding populations using the SNPs linked with the subunits of interest.

Whole-Genome Resequencing Identifies the Molecular Genetic Cause for the Absence of a Gy5 Glycinin Protein in Soybean PI 603408

During ongoing proteomic analysis of the soybean (Glycine max (L.) Merr) germplasm collection, PI 603408 was identified as a landrace whose seeds lack accumulation of one of the major seed storage glycinin protein subunits. Whole genomic resequencing was used to identify a two-base deletion affecting glycinin 5 The newly discovered deletion was confirmed to be causative through immunological, genetic, and proteomic analysis, and no significant differences in total seed protein content were found to be due to the glycinin 5 loss-of-function mutation per se In addition to focused studies on this one specific glycinin subunit-encoding gene, a total of 1,858,185 nucleotide variants were identified, of which 39,344 were predicted to affect protein coding regions. In order to semiautomate analysis of a large number of soybean gene variants, a new SIFT 4G (Sorting Intolerant From Tolerated 4 Genomes) database was designed to predict the impact of nonsynonymous single nucleotide soybean gene variants, potentially enabling more rapid analysis of soybean resequencing data in the future.

Transcriptome Profile of Near-Isogenic Soybean Lines for β-Conglycinin α-Subunit Deficiency during Seed Maturation

Crossing, backcrossing, and molecular marker-assisted background selection produced a soybean (Glycine max) near-isogenic line (cgy-2-NIL) containing the cgy-2 allele, which is responsible for the absence of the allergenic α-subunit of β-conglycinin. To identify α-null-related transcriptional changes, the gene expressions of cgy-2-NIL and its recurrent parent DN47 were compared using Illumina high-throughput RNA-sequencing of samples at 25, 35, 50, and 55 days after flowering (DAF). Seeds at 18 DAF served as the control. Comparison of the transcript profiles identified 3,543 differentially expressed genes (DEGs) between the two genotypes, with 2,193 genes downregulated and 1,350 genes upregulated. The largest numbers of DEGs were identified at 55 DAF. The DEGs identified at 25 DAF represented a unique pattern of GO category distributions. KEGG pathway analyses identified 541 altered metabolic pathways in cgy-2-NIL. At 18DAF, 12 DEGs were involved in arginine and proline metabolism. The cgy-2 allele in the homozygous form modified the expression of several Cupin allergen genes. The cgy-2 allele is an alteration of a functional allele that is closely related to soybean protein amino acid quality, and is useful for hypoallergenic soybean breeding programs that aim to improve seed protein quality.

Knockdown of the 7S globulin subunits shifts distribution of nitrogen sources to the residual protein fraction in transgenic soybean seeds

KEY MESSAGE

A platform of gene silencing by amiRNA had been established in fertile transgenic soybean. We demonstrated that knockdown of storage protein shifted the distribution of nitrogen sources in soybean seeds. Artificial microRNAs (amiRNAs) were designed using the precursor sequence of the endogenous soybean (Glycine max L. Merrill) miRNA gma-miR159a and expressed in transgenic soybean plants to suppress the biosynthesis of 7S globulin, which is one of the major storage proteins. Seed-specific expression of these amiRNAs (amiR-7S) resulted in a strong suppression of 7S globulin subunit genes and decreased accumulation of the 7S globulin subunits in seeds. Thus, the results demonstrate that a platform for gene silencing by amiRNA was first developed in fertile transgenic soybean plants. There was no difference in nitrogen, carbon, and lipid contents between amiR-7S and control seeds. Four protein fractions were collected from defatted mature seeds on the basis of solubility at different pH to examine the distribution of nitrogen sources and compensatory effects. In the whey and lipophilic fractions, nitrogen content was similar in amiR-7S and control seeds. Nitrogen content was significantly decreased in the major soluble protein fraction and increased in the residual fraction (okara) of the amiR-7S seeds. Amino acid analysis revealed that increased nitrogen compounds in okara were proteins or peptides rather than free amino acids. Our study indicates that the decrease in 7S globulin subunits shifts the distribution of nitrogen sources to okara in transgenic soybean seeds.

Accumulation of β-conglycinin in soybean cotyledon through the formation of disulfide bonds between α'- and α-subunits

β-Conglycinin, one of the major soybean (Glycine max) seed storage proteins, is folded and assembled into trimers in the endoplasmic reticulum and accumulated into protein storage vacuoles. Prior experiments have used soybean β-conglycinin extracted using a reducing buffer containing a sulfhydryl reductant such as 2-mercaptoethanol, which reduces both intermolecular and intramolecular disulfide bonds within the proteins. In this study, soybean proteins were extracted from the cotyledons of immature seeds or dry beans under nonreducing conditions to prevent the oxidation of thiol groups and the reduction or exchange of disulfide bonds. We found that approximately half of the α'- and α-subunits of β-conglycinin were disulfide linked, together or with P34, prior to amino-terminal propeptide processing. Sedimentation velocity experiments, size-exclusion chromatography, and two-dimensional polyacrylamide gel electrophoresis (PAGE) analysis, with blue native PAGE followed by sodium dodecyl sulfate-PAGE, indicated that the β-conglycinin complexes containing the disulfide-linked α'/α-subunits were complexes of more than 720 kD. The α'- and α-subunits, when disulfide linked with P34, were mostly present in approximately 480-kD complexes (hexamers) at low ionic strength. Our results suggest that disulfide bonds are formed between α'/α-subunits residing in different β-conglycinin hexamers, but the binding of P34 to α'- and α-subunits reduces the linkage between β-conglycinin hexamers. Finally, a subset of glycinin was shown to exist as noncovalently associated complexes larger than hexamers when β-conglycinin was expressed under nonreducing conditions.

Molecular evolution of glycinin and β-conglycinin gene families in soybean (Glycine max L. Merr.)

There are two main classes of multi-subunit seed storage proteins, glycinin (11S) and β-conglycinin (7S), which account for approximately 70% of the total protein in a typical soybean seed. The subunits of these two protein classes are encoded by a number of genes. The genomic organization of these genes follows a complex evolutionary history. This research was designed to describe the origin and maintenance of genes in each of these gene families by analyzing the synteny, phylogenies, selection pressure and duplications of the genes in each gene family. The ancestral glycinin gene initially experienced a tandem duplication event; then, the genome underwent two subsequent rounds of whole-genome duplication, thereby resulting in duplication of the glycinin genes, and finally a tandem duplication likely gave rise to the Gy1 and Gy2 genes. The β-conglycinin genes primarily originated through the more recent whole-genome duplication and several tandem duplications. Purifying selection has had a key role in the maintenance of genes in both gene families. In addition, positive selection in the glycinin genes and a large deletion in a β-conglycinin exon contribute to the diversity of the duplicate genes. In summary, our results suggest that the duplicated genes in both gene families prefer to retain similar function throughout evolution and therefore may contribute to phenotypic robustness.

Identification of strong aggregating regions in soy glycinin upon enzymatic hydrolysis

Upon hydrolysis with chymotrypsin, soy glycinin has a strong tendency to aggregate. The regions of glycinin from which the aggregating peptides originate were identified by accumulative-quantitative peptide mapping. To this end, the aggregating peptides were further hydrolyzed with trypsin to obtain peptides of which the sequence can be identified using RP-HPLC-MS/MS. This resulted in a hydrolysate in which 90% of the proteinaceous material was dissolved. The soluble fraction was analyzed using the method of accumulative-quantitative peptide mapping: fractionation using ion exchange chromatography, followed by identification of peptides by RP-HPLC-MS/MS, quantification based on the absorbance at 214 nm, and finally peptide mapping. For the peptide mapping the proportions in which each of the five glycinin subunits are present, as determined by Edman degradation, were taken into account. The results showed that mainly the basic polypeptide and a part of the acidic polypeptide, close to the location of the disulfide bridge between the basic and acidic polypeptides, are present in the aggregating peptide fraction. On the basis of the results obtained, an aggregation mechanism was proposed. The hydrophilic acidic polypeptides shield the hydrophobic basic polypeptides, and the former are preferentially degraded upon hydrolysis. This results in a net increase in hydrophobicity of the remaining material, which mainly consists of the basic polypeptide fragments. This increase in hydrophobicity is proposed to be the driving force in the aggregation of chymotrypsin-derived peptides of glycinin.

Micrometer-sized fibrillar protein aggregates from soy glycinin and soy protein isolate

Long, fibrillar semiflexible aggregates were formed from soy glycinin and soy protein isolate (SPI) when heated at 85 degrees C and pH 2. Transmission electron microscopy analysis showed that the contour length of the fibrils was approximately 1 microm, the persistence length 2.3 microm, and the thickness a few nanometers. Fibrils formed from SPI were more branched than the fibrils of soy glycinin. Binding of the fluorescent dye Thioflavin T to the fibrils showed that beta-sheets were present in the fibrils. The presence of the fibrils resulted in an increase in viscosity and shear thinning behavior. Flow-induced birefringence measurements showed that the behavior of the fibrils under flow can be described by scaling relations derived for rodlike macromolecules. The fibril formation could be influenced by the protein concentration and heating time. Most properties of soy glycinin fibrils are comparable to beta-lactoglobulin fibrils.

Functional region identification in proteins by accumulative-quantitative peptide mapping using RP-HPLC-MS

A new method was developed to identify regions in proteins from which peptides are derived with specific functional properties. This method is applicable for systems in which peptides of a hydrolyzed protein possess specific functional properties, but are too large to be sequenced directly and/or the peptide mixture is too complex to purify and characterize each peptide individually. In the present work, aggregating peptides obtained by proteolytic hydrolysis of soy glycinin were used as a case study. The aggregating peptides are isolated and subsequently further degraded with trypsin to result in peptides with a mass <5000 Da to enable sequence identification using RP-HPLC-MS in combination with MS/MS. Prior to RP-HPLC the peptides are fractionated using anion and cation exchange chromatography. The fractions obtained are analyzed with RP-HPLC-MS. The peptides, with identified sequences, were quantified using the peak areas of the RP-HPLC chromatograms measured at 214 nm. Next, the peak areas were corrected for the molar extinction coefficient of the individual peptides, followed by accumulative-quantitative peptide mapping. The results show that in complex systems, based on the method described, the regions in the parental protein from which the functional peptides originate can be properly identified.

Differences in denaturation of genetic variants of soy glycinin

In heat denaturation studies conducted in the past the genetic variants of glycinin have been considered as a homogeneous group of proteins. In this work the validity of this assumption was tested. It was found by calorimetric studies that glycinin denatures heterogeneously at pH 7.6. When the temperature of isothermal treatment is increased from 70 to 82 degrees C the proportion of glycinin remaining native progressively decreases from 95% to 5% while the denaturation temperature of the glycinin remaining native increases from 88.5 to 95 degrees C. Similar trends were found for pH 3.8. Fractionation and subsequent analysis (MALDI-TOF and CE) of isothermally treated samples demonstrated that at pH 7.6 the heterogeneous denaturation is caused by differences in thermal stability of the genetic variants of glycinin. The stability increases in the order G2/G3/G1< A(4)< G5 < G4.

Genetic mapping of the Gy4 and Gy5 glycinin genes in soybean and the analysis of a variant of Gy4

The predominant storage protein of soybean [Glycine max (L.) Merr.] seed is a globulin called glycinin. Thus far five genes encoding glycinin subunits have been described, and these are denoted by the gene symbols Gy1 to Gy5. The objectives of this study were to map two of these genes, Gy4 and Gy5, and to conduct a genetic analysis of a subunit size-variant from an allele of Gy4. For this purpose a population was formed with an interspecific cross between PI 468916 (G. soja) and A81-356022 (G. max). The two size forms of G4, the subunit from Gy4, segregated codominantly in the mapping population, and were due to a short insertion in the hypervariable region of the mutant protein. The biochemical and molecular characteristics of the two subunits indicate that they are produced from alternate alleles of the same gene. The gene symbols Gy (a) and Gy (b) have been assigned to the normal and variant genes, respectively. When genomic DNA from the two parents was probed with a Gy4 cDNA, RFLPs were identified for both Gy4 and Gy5. Using these genetic markers, the Gy4 and Gy5 glycinin genes were mapped in linkage group "O" and "F" on the public soybean genomic map.

Characterization of a Gy4 glycinin gene from soybean Glycine max cv. forrest

The glycinin gene family encoding the glycinin subunits in soybean plants is composed of at least five gene members. A genomic clone lambda S312 containing the Gy4 gene from a genomic library of cv. Forrest was isolated and partially characterized. The organization of this gene was found to be similar to that of a null allele from cv. Raiden, but different from the Gy4 gene from cv. Dare. The complete nucleotide sequence of this gene has been determined. It is 2599 bp long consisting of four exons and three introns. Comparing the DNA sequences between this gene and the gene from Dare and a null allele from Raiden, the difference found in the coding region was 5'-GCAGTGCAAG-3' (nt 824 to 833) in the former case versus 5'-TGGAGTTGCAATT-3' (nt 1314 to 1326) in the latter case in the exon 2 domain, resulting in three amino acid differences and one amino acid absence. Some other differences were also found in the non-coding region. The coding sequence and 5'-flanking region of the Gy4 gene, when compared with that of other legumin genes as well as group 1 glycinin subunit genes, revealed some interesting features: (1) a transposable element-like sequence was found in the hypervariable region (HVR) of the exon 3 domain, which was lacking in the legumin and the glycinin group 1 genes; (2) in the 5'-flanking region from nt -145 to -1, two high-homology sequences were found: one from nt -141 to nt -132, the other from nt -118 to nt -92 which includes the 'legumin box' and the RY repeat element.

An attempt to elucidate the origin of cultivated soybean via comparison of nucleotide sequences encoding glycinin B4 polypeptide of cultivated soybean, Glycine max, and its presumed wild progenitor, Glycine soja

Nucleotide sequences of cDNAs encoding soybean glycinin B4 polypeptide were compared for three soybean cultivars and two introductions of wild soybean, G. soja. For three G. max cultivars, only two nucleotide substitutions were found, while G. max and G. soja nucleotide sequences had four substitutions. These data give added proof that G. max originated from G. soja. On the other hand, the time required for the accumulation of four nucleotide substitutions (calculated from the parameters of 11S globulin molecular evolution) appeared to be longer than the duration of the soybean domestication period.

Molecular cloning, genomic organization, expression and evolution of 12S seed storage protein genes of Arabidopsis thaliana

We have identified a number of genes of the flowering plant Arabidopsis thaliana that are abundantly expressed during embryogenesis. In this paper we discuss four of these genes, which comprise a gene family: complete genomic nucleotide sequence of two of the genes and partial sequence of the other two shows that they are all homologous to the 12S globulin seed storage protein genes of other angiosperms. The four genes fall into three subfamilies, as defined by cross-hybridization. One subfamily contains two genes in the Landsberg erecta strain, but only a single gene in the Columbia strain of Arabidopsis. The other two of these 12S gene subfamilies contain only single genes in both strains. Thus, the seed storage protein gene family in Arabidopsis appears much simpler than that in other higher plants.These genes are expressed during the latter half of embryogenesis, a period in which abscisic acid (ABA) is thought to play a role in gene regulation, and known to play a role in seed physiology. We observed no significant difference in the expression profiles of these four genes in ABA-deficient and ABA-insensitive mutants of Arabidopsis, except that the onset of detectable expression of all of the transcripts is slightly delayed in both types of mutants.

Isolation and sequence of cDNA encoding the soybean protease inhibitors PI IV and C-II

Two full-length (or nearly so) cDNA clones containing information for the protease inhibitors PI IV and C-II from soybean seeds were identified by means of a synthetic probe. DNA sequencing revealed that the two protease inhibitors are synthesized as precursors with a short peptide leader. The coding regions of the two clones show 80% homology, wheraes the 5' non-coding regions are 90% homologous. Homology of 75% is found in the region extending beyond the stop codons.

The complete deduced amino acid sequences of legumin β-polypeptides from different genetic loci inPisum

The deduced amino acid sequences of the β-polypeptides ofPisum legumin from two loci on chromosome 1 were compared with one from a locus on chromosome 7. The chromosome 1-derived sequences were ∼80% identical, but each was only ∼50% homologous to the chromosome 7-derived sequence. Comparison of these sequences with those of homologous polypeptides from two other species of the Leguminoseae showed that the chromosome 1-derivedPisum sequences were more similar to legumin B than to legumin A fromVicia faba and were more closely related to group II than to group I glycinins fromGlycine max. The converse was true for the chromosome 7-derivedPisum sequences. This suggests that divergence of legumin-like sequences predated speciation in these three members of the Leguminosease.Among the threePisum sequence classes, a highly variable region was identified within the α-polypeptide, just to the amino-terminal side of the αβ processing site. This region varied considerably in length within the three classes ofPisum α-polypeptide sequence, a variation which far exceeded that which has previously been described for other legumins and glycinins. The chromosome 7-derived, and one of the chromosome 1-derived α-polypeptide sequences contained different tandem repeats in this region.

Isolation and characterization of cDNAs encoding oat 12S globulin mRNAs

A cDNA library was made from poly(A(+)) RNA isolated from developing oat seeds, and oat globulin cDNA clones were identified by hybridization with synthetic oligonucleotides. Globulin clones were characterized by restriction enzyme mapping and cross-hybridization analysis. Based on these comparisons, four classes of globulin clones were distinguished. These clones hybridized to multiple DNA fragments in restriction enzyme digests of oat genomic DNA, indicating that the genes exist in a multigene family. The nucleotide sequence of one of the globulin cDNA clones was determined. The amino acid sequence derived from the DNA sequence verified its identity as an oat globulin and confirmed that the protein is synthesized as a precursor similar to legume 11S storage globulins. The basic polypeptide encoded at the 3' end of the mRNA was found to be homologous to the basic polypeptides of other 11S seed globulins.