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

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Soybean is one of the most important field crops grown in the United States. Commercial soybeans contain about 36 - 40% protein and 18 - 20% oil, by dry weight. Most of the soybean produced in the U.S. is utilized for oil production and animal feed. Even though soybean is a rich source of protein for livestock and humans, the nutritional quality of soybean can be further enhanced if the concentration of sulfur containing amino acids, methionine and cysteine, can be increased. Previously, our lab has employed transgenic approaches to increase the nutritive value of soybean by expressing heterologous sulfur-rich seed proteins and by manipulating the sulfur assimilatory pathway. Even though modest improvement in the nutritive value has been obtained by these approaches, till now no high yielding soybean cultivars with high protein and high sulfur amino acid content has been developed. Such cultivars will be of great value for the agricultural industry especially in animal feed. In this study, I have crossed a South Korean high protein soybean line (Lee5) with a transgenic soybean line with elevated sulfur amino acid content (CS) and developed soybean experimental lines that were advanced to F4:5 seeds. Theses experimental lines exhibit both high protein and high sulfur amino acid content. The protein content of their seeds has been increased 8 to 14% while their oil content has decreased 5 to 7% when compared with CS. Furthermore, I have successfully introduced the cytosolic isoform of O-acetylserine sulfhydrylase (OASS), the overexpressed transgene, from CS into these crosses. The activity of OASS has been increased 5 to 20-fold in experimental lines when compared to Lee5.