Identification of a new soybean Kunitz trypsin inhibitor mutation and its effect on Bowman-Birk protease inhibitor content in soybean seed

Authors: Gillman, Jason; KIM, WON-SEOK - University Of Missouri; Krishnan, Hari

Submitted to: Journal of Agricultural and Food Chemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/22/2015
Publication Date: 1/22/2015
Publication URL: https://handle.nal.usda.gov/10113/60531
Citation: Gillman, J.D., Kim, W., Krishnan, H.B. 2015. Identification of a new soybean Kunitz trypsin inhibitor mutation and its effect on Bowman-Birk protease inhibitor content in soybean seed. Journal of Agricultural and Food Chemistry. 63:1352-1359.

Interpretive Summary: Soybean seeds are the pre-eminent source of high quality protein, which is a major supplier of essential amino acids to animal feed mixtures. Soybean, like many legumes, has certain anti-nutritional proteinase inhibitors which prevent the efficient activity of digestive enzymes. For optimal nutrition, these inhibitors must be inactivated, which requires expensive and energy costly heat processing for the feed processor. We have identified a new soybean line that has reduced anti-nutritional protein factors and combined it with another soybean line that reduced the anti-nutritional protein factors further. Our results revealed that there are additional undetermined genetic factors that may play a major role in controlling the level of antinutritional protein factors in soybean seeds. This research impacts the US breeding capability to tailor animal feed constituents for optimal animal growth and well-being.

Technical Abstract: Soybean seeds possess anti-nutritional compounds which inactivate digestive proteases, principally corresponding to two families: Kunitz Trypsin Inhibitors (KTi) and Bowman-Birk Inhibitors (BBI). High levels of raw soybeans/soybean meal in feed mixtures can cause poor weight gain and pancreatic abnormalities via inactivation of trypsin/chymotrypsin enzymes. Soybean protein meal is routinely heat treated to inactivate inhibitors, a practice which is energy intensive, costly and can degrade certain essential amino acids. In this work, we identified a new soybean germplasm accession which has reduced Kunitz trypsin inhibitor activity due to mutations affecting an isoform annotated as non-functional (KTi1), which was synergistic with a previously identified mutation (KTi3-); seeds homozygous for both mutations lack any detectable KTi protein. We observed significant proteome rebalancing in all KTi mutant lines, resulting in dramatically increased BBI protein levels. However, the overexpressed BBI isoforms are likely non-functional, as chymotrypsin inhibition declined in all KTi mutant lines.