ARCHAMBAULT, ANNIE* and ANNE BRUNEAU. Institut de recherche en biologie vegetale (Universite de Montreal), 4101 est rue Sherbrooke, Montreal (Quebec), Canada H1X 2B2. - How useful is the LEAFY gene for the phylogeny reconstruction in the Caesalpinioideae?
We evaluated the potential of the LEAFY gene, a nuclear gene,
as a phylogenetic marker in the subfamily Caesalpinioideae of the
Leguminoseae. Caesalpinioideae are large tropical trees which are
extremely diverse in their floral morphology. The LEAFY gene
has a crucial role in the transition to flowering, and in Pisum
sativum, it also is responsible for the pinnate nature of the
leaves. In all angiosperms examined to date the coding sequence is
separated by two introns. We cloned and sequenced the 3’ portion of
the second exon, the second intron, and most of the third exon of the
LEAFY gene for a representative sampling of species in the
Caesalpinioideae and for a few other legumes. The phylogenetic
analyses tell us that the gene is in a single copy. The intron is too
variable to be useful for resolving relationships across the
Caesalpinioideae, but the exons can be aligned and provide
phylogenetic resolution. We have found a new intron inserted in the
second exon, which serves as a marker for a group of genera in tribe
Detarieae. The trees recovered from the phylogenetic analyses of the
exons are highly resolved compared to those obtained from chloroplast
sequences (trnL intron) and the groups are strongly supported.
However, the results from the phylogenetic analysis of LEAFY
are not congruent with those from the trnL intron sequences,
and they differ from traditional hypotheses of relationships in the
subfamily. What are the biological mechanisms that lead to this
incongruence? Is LEAFY a poor phylogenetic marker? Possible
causes for this incongruence are explored : saturation of
non-synonymous substitutions in LEAFY, presence of undetected
multiple copies in certain taxa, differences in evolutionary rates
among lineages.
Key words: Caesalpinioideae, incongruence, LEAFY gene, Molecular phylogeny