Lectin and lectin-related proteins in Lima bean (Phaseolus lunatus L.) seeds: biochemical and evolutionary studies

Lectin-related polypeptides are a class of defence proteins found in seeds of Phaseolus species. In Lima bean (P. lunatus), these proteins and their g enes have been well characterized in the Andean morphotype, which represent s one of the two gene pools of this species. To study the molecular evoluti on of the lectin family in Lima bean we characterized the polypeptides belo nging to this multigene family and cloned the genes belonging to the Mesoam erican gene pool. The latter gene pool contains components similar to those of the Andean pool, namely: an amylase inhibitor-like (AIL), an arcelin-li ke (ARL) lectin and the less abundant Lima bean lectin (LBL). These protein s originate from an ancestor gene of the lectin type which duplicated to yi eld the lectin gene and the progenitor of ARL and AIL. In this species, ARL represents an evolutionary intermediate form that precedes AIL. Phylogenet ic analysis supports an Andean origin for Lima bean. The molecular evolutio nary studies were extended to the genes of common bean and demonstrated tha t true lectin genes and the ancestor of lectin-related genes are the result of a duplication event that occurred before speciation. Lima and common be an followed different evolutionary pathways and in the latter species a sec ond duplication event occurred that gave rise, in Mesoamerican wild genotyp es, to arcelin genes.