Variation within the Binding Loops of Bowman-Birk Inhibitors in Common Bean (Phaseolus vulgaris L.)

To understand better the binding loop polymorphism existing within and between the two common bean gene pools, we have isolated and sequenced the BBI obtained from 16 samples belonging to both Mesoamerican and Andean gene pool (6 and 10 samples, respectively). Genomic DNA was extracted from young leaves and BBI sequences were amplified by PCR using two specific primers designed on the partial gene sequence encoding for the Bowman-Birk type inhibitor (Piergiovanni and Galasso, 2004). The amplified product of about 300 bp was gel purified and cloned in pGEM®T plasmid (Promega, USA). Several clones for each sample were sequenced with an automated sequencer. By comparing the inserts of 104 clones, it were found 37 BBI types sharing 91 to 99% of similarity. The two types more frequent were found in more than 50% of tested common beans. The substitutions detectable by comparing the 37 BBI types generally involved more than one residue located outside as well as within the trypsin and the chymotrypsin binding loops.