Nucleotide sequence of a cDNA encoding a low molecular weight sulfur-rich protein in soybean seeds

Developmental and environmental regulation of soybean SE60 gene expression during embryogenesis and germination

Soybean SE60 belongs to the gamma-thionin family of proteins. We recently demonstrated that SE60 plays a role in defense during soybean development. Here, we show that SE60 is expressed in a tissue-specific and developmentally regulated manner. The expression of SE60 is distinct from that of the glycinin (Gy2) and extensin (SbHRGP3) genes of soybean during embryogenesis and germination. A SE60::GUS(-809) transgene, comprising -809 bp of the 5'-flanking region of SE60 fused to the GUS reporter gene, was expressed specifically in developing embryos, but not in the endosperms, from the globular stage of transgenic tobacco and Arabidopsis seeds. Furthermore, light affected the SE60::GUS(-809) expression pattern in germinating seedlings. Electrophoretic mobility shift assay (EMSA) revealed that soybean nuclear proteins as well as E. coli-expressed SB16, a high mobility group protein (HMG), were bound sequence-specifically to the fragment containing AT-rich motifs identified in the SE60 promoter. Interestingly, the soybean nuclear proteins binding to the two G-boxes and RY repeat were prevalent in seeds of 2-4 mm in size. In contrast, the nuclear proteins binding to the AT-rich motif and SE60 RNA expression were more prominent in seeds of 4-6 mm in size. Therefore, we propose that factors binding to the G-boxes or RY repeat initiate SE60 expression during embryogenesis.

Antimicrobial activity of gamma-thionin-like soybean SE60 in E. coli and tobacco plants

The SE60, a low molecular weight, sulfur-rich protein in soybean, is known to be homologous to wheat gamma-purothionin. To elucidate the functional role of SE60, we expressed SE60 cDNA in Escherichia coli and in tobacco plants. A single protein band was detected by SDS-polyacrylamide gel electrophoresis (SDS-PAGE) after anti-FLAG affinity purification of the protein from transformed E. coli. While the control E. coli cells harboring pFLAG-1 showed standard growth with Isopropyl beta-d-1-thiogalactopyranoside (IPTG) induction, E. coli cells expressing the SE60 fusion protein did not grow at all, suggesting that SE60 has toxic effects on E. coli growth. Genomic integration and the expression of transgene in the transgenic tobacco plants were confirmed by Southern and Northern blot analysis, respectively. The transgenic plants demonstrated enhanced resistance against the pathogen Pseudomonas syringae. Taken together, these results strongly suggest that SE60 has antimicrobial activity and play a role in the defense mechanism in soybean plants.

Seed storage protein composition of non-nodulating soybean (Glycine max (L.) Merr.) and its influence on protein quality

A 53 kDa protein, which accumulates at low levels in non-nodulating Clark soybeans, was purified by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE). Polyclonal antibodies were raised against the gel-purified protein. N-terminal sequence analysis identified the 53 kDa protein as the beta-subunit of beta-conglycinin. Results from Western blot analysis, using antibodies raised against the purified beta-subunit of beta-conglycinin, revealed that accumulation of this protein was enhanced in non-nodulating soybeans when the plants were supplemented with nitrogen. Results from Northern blot analysis indicate that non-nodulating soybeans in general had lower levels of mRNA for the major soybean seed proteins. A one-time application of nitrogen to non-nodulating soybeans enhanced the accumulation of the 1.6 kb beta-conglycinin beta-subunit mRNA. The mRNA levels of the 2.1 kb beta-conglycinin alpha'-subunit and the 2.2 kb G4 glycinin in the non-nodulating soybeans were several-fold lower than in nodulating soybeans. Nitrogen application had no effect on the abundance of these RNA transcripts. The amount of RNA encoding an 8.5 kDa sulfur-rich protein was two-fold higher in non-nodulating soybeans when compared with nodulated soybeans. Nitrogen application reduced the abundance of this transcript to levels comparable with those of nodulated soybeans. Despite lower levels of the beta-subunit of beta-conglycinin, the methionine content of the total seed protein fraction was lower than that of nodulated soybeans. In contrast, non-nodulating soybeans contained more cysteine than nodulating soybeans.

Tissue-specific and developmental regulation of a gene encoding a low molecular weight sulfur-rich protein in soybean seeds

A gene corresponding to a cDNA clone, SE60, encoding a low molecular weight sulfur-rich protein in soybean seeds was isolated from a soybean genomic library and characterized at the nucleotide level. The SE60 gene is interrupted by an intervening sequence of 694 bp in size. The 5' flanking region of the gene contained various regulatory sequences such as the RY repeat and CACA elements found in other seed protein genes of legumes. The SE60 gene encoded a preprotein of 75 amino acids, having a signal sequence of 28 amino acids at the N-terminus. The mature protein of 47 amino acids was basic and cysteine-rich. Northern blot analysis suggested that the SE60 gene is expressed in a tissue-specific and developmentally regulated manner during soybean seed development. The SE60 genes form a small multigene family composed of about four members in the soybean genome.

Pseudothionin-St1, a potato peptide active against potato pathogens

A 5-kDa polypeptide, pseudothionin Solanum tuberosum 1 (Pth-St1), which was active against Clavibacter michiganensis subspecies sepedonicus, a bacterial pathogen of potatoes, has been purified from the buffer-insoluble fraction of potato tubers by salt extraction and HPCL. Pth-St1 was also active against other potato pathogens tested (Pseudomonas solanacearum and Fusarium solani). The N-terminal amino acid sequence of this peptide was identical (except for a N/H substitution at position 2) to that deduced from a previously reported cDNA sequence (EMBL accession number X-13180), which had been misclassified as a Browman-Birk protease inhibitor. Pth-St1 did not inhibit either trypsin or insect alpha-amylase activities, and, in contrast with true thionins, did not affect cell-free protein synthesis or beta-glucuronidase activity. Northern-blot and tissue-print analyses showed that steady-state mRNA levels were highest in flowers (especially in petals), followed by tubers (especially in the epidermal cell layers and in leaf primordia), stems and leaves. Infection of leaves with a bacterial pathogen suspended in 10 mM MgCl2 switched off the gene, whereas mock inoculation with 10 mM MgCl2 alone induced higher mRNA levels.