真雙子葉植物基群花部B群基因之演化研究
Date Issued
2004
Date
2004
Author(s)
DOI
922621B002022
Abstract
Although the floral ABC model is
generally accepted as ubiquitous in flowering
plants, variation in gene expression has been
found in basal angiosperms and basal eudicots.
Accordingly, the basal eudicots and basal core
eudicots show highly variable floral features
in terms of flower size and floral organ
numbers, such as the absence of perianth in
Trochodendron aralioides and reduced
flowers in Santalales. These plants are indeed
critical to understand the evolutionary
developmental program of perianth evolution
in flowering plants. Previous studies have
shown that there is a major duplication event
of all ABC class genes along the branch
leading to core eudicot lineages. However,
only one of the two B class homologues
(AP3-like) is found duplicated and fixed in
this major event, i.e. to euAP3 and TM6
sublineages, but not the PI-like homologues.
Such duplication may be responsible to the
diversification of floral features among basal
eudicots. Here we selected representative taxa
in flowering plants to examine the evolution B
class gene duplications and the change of
selection pressure among lineages. Seventeen
cDNA clones encoding B class gene
homologues were newly determined from
Buxus microphylla ssp. sinica,
Trochodendron aralioides, Dillenia indica,
Thesium chinense, Loranthus kaoi and
Loranthus delavayi. All of these taxa have
one to three PI homologues, and various AP3
homologues. Results from phylogenetic
analysis suggest that the first two taxa have
paleoAP3 homologues whereas the later four
are most likely having either TM6 or euAP3-
like homologues instead. Based on
phylogenetic analysis, we proposed the
euAP3/TM6 duplication occurred after the
separation of the Trochodendraceae but
before the divergence of the core eudicots.
Furthermore, the analysis for detecting
selective constraints also suggests that both
PI and AP3 lineages have been subjected to
strong purifying selection, and the switch of
selective constraint is apparently present
between basal eudicots and core eudicots. A
thorough survey is necessary to elucidate the
correlations between gene duplications and
the selective constraints among different
clades of basal and core eudicots.
Subjects
Eudicots
B-class gene
gene duplication
selective constraint
Publisher
臺北市：國立臺灣大學生態學與演化生物學研究所
Type
other
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