(American Society of Plant Biologists) -- Biotechnology enhanced soybeans with tryptophan levels that are up to 30 times higher than traditionally bred seeds have been grown over 5 generations. Soybeans are a major source of nitrogen and amino acids (AAs) for animal feeds. In many feed rations, the AAs lysine and methionine are limiting unless synthetic versions of these AAs are added to the ration, then a second-tier of AAs become limiting. Tryptophan is included in this group where the high cost of synthetic second-tier AAs may limit their use.

Anthranilate synthase (AS) catalyzes one of the key steps in the biosynthetic pathway for tryptophan production in plants. To increase tryptophan content in soybean seeds, a variant of the maize AS gene that is insensitive to tryptophan inhibition was expressed in soybean using a seed specific promoter. Protein and oil of high tryptophan seeds were not significantly different from the traditionally bred controls. Additional testing, including agronomic performance and metabolic profiling are underway.

The research findings were presented by Jihong Liang during a mini-symposium on Metabolic Engineering at the American Society of Plant Biologists (ASPB) annual meeting in the Hawaii Convention Center, Honolulu, Hawaii.