The characterization of floral organ identity gene homologues in Trochodendron aralioides Sieb. & Zucc.
Date Issued
2005
Date
2005
Author(s)
Wu, Hsiu-Chung
DOI
en-US
Abstract
Trochodendron aralioides is the sole member of the family Trochodendraceae, and is restricted to Taiwan, the Ryukyu Islands, Japan, and South Korea. T. aralioides has vesselless wood and lacks a perianth, therefore for some time it has been suggested as one of the most primitive angiosperms. But according to detailed morphological and anatomical studies, and molecular phylogenetic analyses, it is widely accepted now that Trochodendron belongs to a more derived group in angiosperms, the basal eudicots. In 1986, Endress demonstrated that there are a few residual scales located between the prophylls and the stamens of T. aralioides, and called those residue organs “tepals”. Our observations showed that there are more scales appearing serially from prophylls to tepals in our samples than that Endress reported. Furthermore, we found that the number of scales differs slightly between protandrous and protogynous flowers. The epidermal cells on the floral parts are more or less papillate, similar to the epidermal cells of ordinary showy petals of other species. The results suggest that the perianth of Trochodendron is very likely reduced during evolution instead of being a pleiomorph in the angiosperms, and the perianth has been replaced by the whole inflorescence as the attracting agent. In order to elucidate the underlying mechanism of floral organ formation, we have characterized putative floral organ identity genes in T. aralioides. Previously, investigators cloned three B class homologues from T. aralioides, we have built on that previous work by successfully cloning one A class, two C class, and four E class homologous genes from this species. The sequences all show distinct C-terminal motifs corresponding to the previously characterized ACE class genes, and phylogenetic analysis confirmed these identities. The phylogenetic analysis also supports Trochodendron as a member of basal eudicots based on the identified gene sequences. The RT-PCR expression patterns for those floral identity gene homologues do not match well to the current floral ABCDE model. Whether or not the discrepancy is due to a deviation from the standard model or due to methodological limitations awaits further examination, such as immunolocalization studies or other functional assays.
Subjects
昆欄樹
花部器官決定性基因
花部發育
Trochodendron aralioides
floral development
ABC model
Type
other
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