Bowman-Birk inhibitors in Lens: identification and characterization of two paralogous gene classes in cultivated lentil and wild relatives

In order to investigate the genetic structure of lentil Bowman-Birk inhibitors (BBIs), primers were designed on pea BBI sequences. The sequences obtained from lentil DNA, using these primers, indicate that lentil possesses at least two paralogous genes. Protein sequences translated in silico from lentil DNA sequences suggest that the two coded proteins are highly similar to Pisum trypsin inhibitor TI1 and TI6 BBIs, respectively. In fact, both are double-headed inhibitors, one class showing the presence of a trypsin- and a chymotrypsin-reactive site, the other showing two trypsin-inhibition sites, similar to pea TI1 and TI6, respectively. The same primers were used to amplify sequences from the DNA of other Lens species. The results strongly support that all species of Lens possess the same classes of BBI coding genes, orthologous to those identified in the cultivated lentil. Lens nigricans showed the most diverging sequences both at the nucleotide and the amino acid level. The similarity of the two gene classes identified in the genus Lens to those of Pisum and the observations that the patterns of expression of the Lens genes are equivalent to those of pea orthologous genes, possibly imply that BBIs in Lens are coded by gene classes with similar genome organization and function to those of pea. Finally, a phyletic analysis, based on the comparison of sequences obtained from other species belonging to the Vicieae tribe of the Fabaceae family, strongly suggests that all Vicieae could have a similar genome organization and function for BBI genes, and that this could be a general rule in all the Fabaceae family.