Proceedings of the XLVI Italian
Society of Agricultural Genetics - SIGA Annual Congress
Giardini
Naxos, Italy - 18/21 September, 2002
ISBN 88-900622-3-1
Poster
Abstract - 3.24
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.