CHARACTERIZATION OF A SOYBEAN (GLYCINE MAX (L.) MERR.) MUTANT WITH REDUCED LEVELS OF KUNITZ TRYPSIN INHIBITOR

Authors: Krishnan, Hari

Submitted to: Plant Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/3/2001
Publication Date: 4/1/2001
Citation: KRISHNAN, H.B. CHARACTERIZATION OF A SOYBEAN (GLYCINE MAX (L.) MERR.) MUTANT WITH REDUCED LEVELS OF KUNITZ TRYPSIN INHIBITOR. PLANT SCIENCE. 2001. v. 160(5). p. 979-986.

Interpretive Summary: In the United States, the majority of soybean seeds are used in animal feed. Soybeans contain high levels of trypsin inhibitors (anti-nutritional proteins). This causes poor digestion of dietary proteins by inhibiting the pancreatic enzymes. Reducing or eliminating trypsin inhibitors will greatly improve the nutritional value of soy proteins and help to dispel the perceived inferiority image of soy proteins. This study characterizes a soybean mutant with reduced levels of trypsin inhibitors and provides a molecular basis for their reduced accumulation. This information will help agronomists and biotechnologists to design soybeans lacking trypsin inhibitor so that raw soybeans can be fed to animals without prior heat treatment.

Technical Abstract: Kunitz trypsin inhibitor, an abundant soybean [Glycine max (L.) Merr.] seed protein, has a molecular mass of 21,500 daltons and is specific for serine proteases. A soybean mutant (P.I. 196168) was characterized to determine the molecular basis for reduced Kunitz trypsin inhibitor levels during seed development. Western blot analysis revealed that P.I. 196168, in comparison nto Amsoy 71, accumulated low amounts of Kunitz trypsin inhibitor protein. Non-denaturing polyacrylamide enzyme activity gels indicated that Amsoy 71 seeds contained at least five distinct zones of trypsin inhibitor activity. However, P.I. 196168 contained only four zones of enzyme inhibition. The coding region of the most abundant trypsin inhibitor gene (KTi3) was isolated from Amsoy 71 and P.I. 196168 by PCR. DNA sequence comparisons of the Kunitz trypsin inhibitor coding regions revealed two deletions and one G-to-T transversion have occurred. These mutations introduced four stop codons in the reading frame, resulting in a truncated protein. Northern blot analysis showed that P.I. 196168 accumulated drastically lower amounts of KTi mRNA when compared with Amsoy 71.