Characterization of the Glycinin Gene Family in Soybean

Abstract

We characterized the structure, organization, and expression of genes that encode the soybean glycinins, a family of storage proteins synthesized exclusively in seeds during embryogenesis. Five genes encode the predominant glycinin subunits found in soybeans, and they have each been cloned, sequenced, and compared. The five genes have diverged into two subfamilies that are designated as Group-I and Group-II glycinin genes. Each glycinin gene contains four exons and three introns like genes that encode related proteins in other legumes. Two other genes have been identified and designated as "glycinin-related" because they hybridize weakly with the five glycinin genes. Although not yet characterized, glycinin-related genes could encode other glycinin subunit families whose members accumulate in minor amounts in seeds. The three Group-I glycinin genes are organized into two chromosomal domains, each about 45 kilobase pairs in length. The two domains have a high degree of homology, and contain at least five genes each that are expressed either in embryos or in mature plant leaves. Gel blot studies with embryo mRNA, as well as transcription studies with 32P-RNA synthesized in vitro from purified embryo nuclei, indicate that glycinin and glycinin-related genes become transcriptionally activated in a coordinated fashion early in embryogenesis, and are repressed coordinately late in seed development. In addition to transcriptional control processes, posttranscriptional events also are involved in regulating glycinin and glycinin-related mRNA levels during embryogenesis.

Legumin encoding sequences from the Redwood family (Taxodiaceae) reveal precursors lacking the conserved Asn‐Gly processing site

“…Corresponding heterogeneity can be recognized in the precursors presented here, and the areas concerned are homologous in position with the Variable Region I and the Hypervariable Region HVR as defined by Nielsen [5]. Interestingly, the sequences are quite well conserved in the region corresponding to Variable Region II, the position of which is also marked in Fig.…”

“…From comparisons of angiosperm legumins, three regions displaying considerable heterogeneity in sequence and size are known [5]. Corresponding heterogeneity can be recognized in the precursors presented here, and the areas concerned are homologous in position with the Variable Region I and the Hypervariable Region HVR as defined by Nielsen [5].…”

“…2. Alignment of the Glycine legumin Gy2 [3-polypeptide [5] and the homologous region of the CjLeg31 precursor. Preceding Asn residues flanking the cleavage site are depicted and regions homologous to the endoprotease recognition site are underlined.…”

“…1. Most likely, the residues Cys 120 and Cys 341 are involved in disulfide linkage of mature ec-and 13-polypeptides; cysteine residues at homologous position are strictly conserved in angiosperm legumins [5] and have been shown to participate in interpolypeptide linkage [21].…”

“…They function as a source of carbon skeletons and nitrogen to support the initial growth of the seedling, and their structure, biosynthesis, and intracellular transfer are well conserved throughout the species investigated [1]. A most invariable character of legumin precursors hitherto known is the Asn-Gly junction located at that site where cleavage occurs to form the c~-and 13-polypeptides constituting mature legumin subunits, and it was assumed that this site has been highly conserved during evolution [2][3][4][5][6].…”