Title: The characterization of floral organ identity gene homologues in
Trochodendron aralioides Sieb. & Zucc.
M.S. Student: Hsiu-Chung Wu (R92B42020)
Advisor: Dr. Jer-Ming Hu
Abstract:
Trochodendron aralioides is the sole member of the family Trochodendraceae,
and is restricted to Taiwan, Ryukyu Islands, Japan, and South Korea. T. aralioides has
vesselless wood and lacks perianth, therefore for some time it has been suggested as
the most primitive angiosperm. But according to detail morphology, anatomy and
molecular phylogenetic analyses, it is widely accepted now that Trochodendron
belongs to a more derived group in angiosperms, the basal eudicots. In 1986, Peter K.
Endress pointed out that there are a few residue scales located between prophylls and
stamens of T. aralioides, and called those residue organs ‘tepals”. Our observation
showed that there are more scales appearing serially as a gradient from prophylls to
tepals in our samples compared to Endress’s observation. The epidermal cells on the
scales all show conical type which is similar to that on the epidermal cells of ordinary
bright petals. The results suggest that the perianths of Trochodendron are very likely
reduced during evolution instead of being a pleiomorphic character, and the attracting
agent has been replaced by whole flower instead of perianth only. In order to elucidate
the underlying mechanism of floral organ formation, we have characterized putative
floral organs identity genes in T. aralioides. We have successfully cloned one A class,
three B class, two C class, and four E class homologous genes from T. aralioides. The
sequences all show distinct C-terminal motifs corresponding to the previously
identified ABCE genes, and phylogenetic analysis confirmed the identities
correspondingly. Using floral identity gene homologues to construct the phylogeny of
eudicot species, the results all support that T. aralioides belongs to basal eudicots.
RT-PCR was used to determine the organ-level expression pattern of those genes.
However, the expression patterns of those floral identity gene homologous do not
match well to current floral ABCDE model. Whether or not the discrepancy is due to
a modification from standard model or due to methodological distortions, awaits
further examination, such as immunolocalization studies or other function assays.