Proceedings of the XLVI Italian Society of Agricultural Genetics - SIGA Annual Congress
Giardini Naxos, Italy - 18/21 September, 2002
SEQUENCES OF ARCELIN 3 AND 7 AND EVOLUTIONARY RELATIONSHIPS AMONG SEVEN ALLELIC VARIANTS IN WILD BEAN SEEDS
SPARVOLI F.*, LIOI L.**, GALASSO I.**, LANAVE C.***, BOLLINI R.*
*) Istituto di Biologia e Biotecnologia Agraria, CNR, Milano, Italy
**) Istituto del Germoplasma, CNR, Bari, Italy
***) Sezione di Bioinformatica e Genomica Comparata, Bari, ITB, CNR
lectin, seed storage proteins
Arcelin (ARC) a lectin-related protein, found only in wild accessions of common bean (Phaseolus vulgaris L.) has insecticidial properties against the larvae of the Mexican bean weevil (Zabrotes subfasciatus). Arcelin has been described in seven allelic variants based on the electrophoretic patterns of arcelin proteins. Genes encoding arcelin are tightly linked to those encoding phytohemagglutinin (PHA) and a-amylase inhibitor (a-AI), and show high degree of sequences similarity, so they are considered as members of the lectin multigene family. We isolated and sequenced cDNA clones encoding arcelin type 3 and type 7. Sequence data indicated that these proteins are closely related to arcelin 4 and arcelin 5, respectively. All nucleotide sequences were multialigned using CLUSTALW program. Evolutionary analysis was carried out using the programs implemented in the PAUP* package. Genetic distances were calculated by using the General Time Reversible (GTR) model, at non-synonymous positions using the seven known arcelin sequences. Dendrograms were reconstructed by ML with and without the assumption of the Molecular Clock. Arcelins can be divided in three subgroups with types 3 and 4 preceding the other ARC genes, so they colud represent progenitors of the other arcelin genes. The absence of arcelin from cultivated genotypes agree with our results that an independent duplication event occurred in wild Mexican bean, from an ancestral progenitor common to a-amylase inhibitor gene.
Moreover, we investigated on the evolutionary relationships among members of this gene family in P. lunatus and P. vulgaris. Our results show that the lectin genes and the ancestor of the related ones are the result of a duplication event occurred before speciation, then different evolution pathways took place in the two species. In P. lunatus an ancestral lectin gene duplicated to yield the true lectin and the progenitor of arcelin like (ARL) and alpha-amylase inhibitor like (AIL), ARLs being evolutionary intermediate forms that precede AILs. In P. vulgaris the ancestral gene underwent two major duplication events, one originating the true lectin and the lectin-related progenitor, and the other separating ARC from a-AI.