Novel alleles among soybean Bowman-Birk proteinase inhibitor gene families

Trypsin inhibitors have been found in various animals, plants and microorganisms. There were two types of trypsin inhibitors in soybean including Bowman-Birk protease inhibitors (BBI) and Kunitz inhibitors (KTI). The different BBI genes from wild soybean (G. soja) and cultivated soybean (G. max) formed a multigene family. We constructed a cDNA library of cultivar 'SuiNong 14' seed at the R7 growth stage using the SMART Kit. Seventeen contigs or singletons were highly homologous to soybean protease inhibitors. Contigs of 5, 35, 8 and 9 were highly homologous to BBI family members BBI-A1, BBI-A2, BBI-C and BBI-D, respectively. Sequence analyses showed there were novel allelic variations among the 4 BBI members in SuiNong 14. Based on the comparison of soybean seed cDNA libraries from different developmental stages, it was apparent that the expression of trypsin inhibitors increased during seed development in soybean. Phylogenetic analysis of BBI gene sequences among dicotyledonous and monocotyledonous plants demonstrated that these genes shared a common progenitor.