Evolutionary analysis of the APA genes in the Phaseolus genus: wild beans as source of lectin-related resistance factors?

Abstract The APA (Arcelin/Phytohemagglutinin/ -Amylase inhibitor) gene family is composed of various members, present in Phaseolus species and coding for lectin and lectin-related seed proteins having the double role of storage and defense proteins. Here members of the APA family have been identiWed by immunological, functional, and molecular analyses and representative genes were sequenced in nine wild species of Phaseolus. All taxa possessed at least one member of the true lectin gene. No arcelin type sequences have been isolated from the species examined. Among the wild species studied, only P. costaricensis contained an -amylase inhibitor (-AI). In addition P. augusti, P. maculatus, P. microcarpus, and P. oligospermus showed the presence of the lectin-related -amylase inhibitor-like (AIL) genes and -AI activity. Data from Southern blot analysis indicated the presence of only one lectin gene in P. parvulus and P. Wliformis, while an extensive gene duplication of the APA locus was found in the other Phaseolus species. Phylogenetic analysis carried out on the nucleotide sequences showed the existence of two main clusters and clearly indicated that lectin-related genes originated from a paralogous duplication event preceding the development of the ancestor to the Phaseolus genus. The Wnding of detectable -AI activity in species containing AIL genes suggests that exploiting APA genes variability in the Phaseolus genus may represent a valuable tool to Wnd new members that may have acquired insecticidal activities.