Lectin-related resistance factors against bruchids evolved through a number of duplication events

Abstract

Abundant lectin-related proteins found in common beans ( Phaseolus vulgaris L.) have been shown to confer resistance against the larvae of a number of bruchid species. Genes encoding for these proteins are members of the lectin multigene family, the most representative components being arcelins, phytohemagglutinins and alpha-amylase inhibitors. Arcelins have been described in seven variants, some of which are resistance factors against the Mexican bean weevil ( Zabrotes subfasciatus), a major bean predator. In this study the isolation and sequencing of arcelin genes from wild P. vulgaris genotypes, containing Arc3 and Arc7 variants, is reported, and similarities and evolutionary relationships among the seven known arcelins are described. The evolutionary analysis shows that arcelins 3 and 4 cluster together and are the most-ancient variants. A duplication event gave rise to two additional clusters, one comprising arcelins 1, 2 and 6 and separated from the cluster of arcelins 5 and 7. A multiple number of arcelin genes were found in arcelin 3 and 4 genotypes indicating that more than one type of arcelin gene may be present in the same locus. Some of these sequences are reminiscent of ancient duplication events in arcelin evolution demonstrating that arcelins have evolved through multiple duplications. A further aim of this paper was to better understand and describe the evolution of the entire lectin multigene family. Beside arcelins, a number of other types of sequences, such as putative lectins and sequences not easily classifiable, were found in genotypes containing Arc3 and Arc4. These results, together with the evolutionary analysis, indicate that lectin loci are quite complex and confirm their origin by multiple duplication events.