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Title: A FOUR-NUCLEOTIDE BASE-PAIR DELETION IN THE CODING REGION OF THE BOWMAN-BIRK PROTEASE INHIBITOR GENE PREVENTS ITS ACCUMULATION IN THE SEEDS OF GLYCINE MICROPHYLLA PI 440956

Author
item Krishnan, Hari
item KIM, WON SEOK - AGRONOMY DEPT, UNIV OF MO

Submitted to: Planta
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 4/19/2003
Publication Date: 7/1/2003
Citation: KRISHNAN, H.B., KIM, W. A FOUR-NUCLEOTIDE BASE-PAIR DELETION IN THE CODING REGION OF THE BOWMAN-BIRK PROTEASE INHIBITOR GENE PREVENTS ITS ACCUMULATION IN THE SEEDS OF GLYCINE MICROPHYLLA PI 440956. PLANTA. 2003. v. 217. p. 523-527.

Interpretive Summary: Soybeans are a rich source of protein for animal feed. However, soybeans contain antinutritional factors that inhibit the animal performance. Soybeans contain two main antinutritional factors, Kunitz trypsin inhibitor and Bowman-Birk protease inhibitor (BBI). These inhibitors are generally inactivated during commercial processing by heat treatment of soybean meal. Heat inactivation of protease inhibitor, however, destroys some essential amino acids such as cysteine, methionine, and lysine. Therefore, it is highly desirable to identify soybean cultivars that lack these two protease inhibitors. A previous study has shown that Glycine microphylla PI440956 does not accumulate BBI. However, the reason for this was not known. We have cloned and characterized the BBI gene from this wild perennial Glycine species. The BBI gene function was interrupted by mutations resulting in the absence of this protein in the seeds. The information obtained from this basic study will help biotechnologists to genetically reduce the antinutritional proteins in soybean. Soybeans containing less protease inhibitors will improve the overall nutritive value and improve the performance of animals feed on soy meal.

Technical Abstract: The Bowman-Birk protease inhibitor (BBI), an abundant soybean [Glycine max (L.) Merr.] seed protein, is a major antinutritional factor. Nulls for the major soybean BBI have been reported in several of the wild perennial Glycine species including G. microphylla (Benth.) Tind PI 440956. This perennial Glycine species does not accumulate the major BBI and the molecular basis for the absence of the major BBI in this plant introduction (PI) line is not known. We have cloned the BBI gene from G. microphylla PI 440956, G. microphylla PI 505188, and G. max cv. Jefferson and determined its nucleotide sequences. Analysis of the G. microphyllla PI505188 and G. max cv. Jefferson nucleotide sequences revealed a complete open-reading frame encoding the BBI. In contrast, the BBI coding region of G. microphylla PI440956 contained a frameshift mutation that resulted in the introduction of a stop codon at the amino terminal region of the protein. Reverse transcription-polymerase chain reaction analysis revealed that the BBI gene was expressed in developing seeds of G. microphylla PI505188 and G. max cv. Jefferson, but not in developing seeds of G. microphylla PI440956. In contrast, a BBI-related isoinhibitor gene was expressed at similar levels in all three Glycine species. Our results suggest that the frameshift mutation in the BBI coding region is responsible for the absence of BBI in the seeds of G. microphylla PI440956.