Development of soybean experimental lines with enhanced protein and sulfur amino acid content

Authors: ALASWAD, ALLA - University Of Missouri; SONG, BO - University Of Missouri; Oehrle, Nathan; WIEBOLD, WILLIAM - University Of Missouri; MAWHINNEY, THOMAS - University Of Missouri; Krishnan, Hari

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/14/2021
Publication Date: 4/21/2021
Citation: Alaswad, A.A., Song, B., Oehrle, N.W., Wiebold, W.J., Mawhinney, T.P., Krishnan, H.B. 2021. Development of soybean experimental lines with enhanced protein and sulfur amino acid content. Plant Science. 308: Article 110912. https://doi.org/10.1016/j.plantsci.2021.110912.
DOI: https://doi.org/10.1016/j.plantsci.2021.110912

Interpretive Summary: Soybean is excellent source of protein for both humans and livestock. Despite the large protein content, the nutritional quality of soybean protein remains suboptimal due to lower concentrations of sulfur containing amino acids cysteine and methionine. Due to the importance of soybean protein in animal feed, increasing sulfur containing amino acid content in soybean has been a critical goal for breeders to achieve. In addition to protein quality, the recent trend of lower levels of protein concentration among soybean cultivars possess an additional challenge. Hence, there is a critical need to develop soybean cultivars with relatively higher levels of protein with improved nutritional quality. In this study, we have crossed a transgenic soybean line with elevated levels of sulfur amino acid content with a high protein soybean cultivar. The resulting experimental lines exhibited elevated protein content along with improved cysteine and methionine profiles. The development of such high protein soybean lines with enhanced sulfur containing amino acids represents a significant achievement that bodes well for retaining the prominence of US soybean as the eminent protein source in animal feed. These newly developed lines can be exploited by soybean breeders to develop elite’s soybean lines with desirable agronomic characteristics and marketable components in the future.

Technical Abstract: Soybean is the preferred protein source for both poultry and swine feed. However, this preferred status is being challenged due to competition from alternative feed ingredients. To overcome this, it becomes necessary for breeders to develop soybean cultivars that contain higher protein and better nutritional composition. In this study, we have developed experimental soybean lines that not only contain significantly higher amounts of protein but also improved sulfur amino acid content. This objective was achieved by crossing a O-acetylserine sulfhydrylase (OASS) overexpressing transgenic soybean line with elevated levels of sulfur amino acid content (CS) with a high protein Korean soybean cultivar (Lee 5). Introgression of high protein and overexpression of OASS was monitored in the experimental lines at each successive generation (F2-F6) by measuring protein content and OASS activity. The average protein content of transgenic CS and Lee 5 seeds were 34.8 % and 44.7 %, while in the experimental soybean lines the protein content ranged from 41.3 %–47.7 %, respectively. HPLC and inductively coupled plasma-mass spectrometry analyses revealed that all the experimental lines developed in this study contained significantly higher amounts of sulfur containing amino acids and elemental sulfur in the seeds. The sulfur amino acid (cysteine'+'methionine) content of the experimental lines ranged from 1.1 % to 1.26 % while the parents Lee 5 and CS had 0.79 % and 1.1 %, respectively. SDS-PAGE and western blot analysis demonstrated that the accumulation of Bowman-Birk protease inhibitor and lunasin, two sulfur amino acid rich peptides, were elevated in experimental soybean lines. High-resolution 2D-gel electrophoresis and Delta2D gel analysis validated that an overall increase in the different subunits of 7S ß-conglycinin and 11S glycinin were mainly responsible for the observed increase in the total amount of protein in experimental lines.