Sequence Analysis of the Arcelin-Phytohaemagglutinin-α-Amylase Inhibitor (APA) Locus in Three Phylogenetically Arrayed Phaseolus vulgaris Clones

Abstract APA is a multigene locus that comprises the protein genes of arcelin (Arc), phytohemagglutinin (PHA) or lectin, and an α-amylase inhibitor (α-AI). These genes play essential roles in the defense responses of legume seeds to protect against seed weevils in common bean (P. vulgaris). During the evolution of this complex locus, PHA proteins appeared first, followed by α-AI and Arc proteins. This study compared and analyzed the sequences of three bacterial artificial chromosome (BAC) clones containing APA fragments of the genotypes G02771, BAT93 and DGD1962. These three genotypes are recognized as representative of the crucial steps of APA evolution in common bean. Our findings demonstrated that rearrangements during evolution can be used to characterize the APA locus, but concurrent adjacent gene regions on either side of the APA locus are highly conserved. Part of the instability of the APA locus may be due to the insertion of retroelements and gene conversion.