- 學位論文
昆欄樹之花部器官決定性同源基因之鑑定與性質分析
The characterization of floral organ identity gene homologues in Trochodendron aralioides Sieb. & Zucc.
摘要
昆欄樹(昆欄樹科)是一種相當獨特的植物，僅分佈於台灣、日本、琉球群島以及南韓；它的花沒有花被構造，木質部沒有導管組織，因此曾經被認為是很原始的被子植物。但近年來從其他形態細部構造及分子譜系分析得到的證據，發現昆欄樹並非被子植物基群(basal angiosperms)，而是屬於真雙子葉植物(Eudicots)基群。1986年Peter Endress利用掃描式電子顯微鏡觀察昆欄樹花部構造，發現在靠近雄蕊的基部有疑似花被退化的器官。我們的觀察發現花托上退化的鱗片狀構造數目比Endress所觀察到的多，而且數目可能和雌先熟或雄先熟的個體差異有關。此外，藉由掃描式電子顯微鏡觀察花部的表皮細胞形態，發現在所有的花部表皮細胞都呈現不同程度的乳突狀(papillate)突起。這種表皮細胞形態多發現於一般花瓣，而這種細胞形態有助於反射光線，使得組織看起來比較明亮。因此由觀察的結果推測，昆欄樹的花被構造可能在演化的過程中遺失，而花被吸引傳粉者的功能可能由整朵花序所取代。為了了解昆欄樹花部器官可能的調控機制，本論文進行昆欄樹之花部器官決定性同源基因的選殖。除了先前研究所選殖出三個B class同源基因之外，本實驗結果共選殖出二個A class同源基因，二個C class同源基因，四個E class同源基因。利用這些花部器官決定基因所建立之譜系關係都支持昆欄樹的演化位置的確在真雙子葉基群。然而從RT-PCR的結果發現，這些選殖出來的花部器官決定性同源基因表現位置並不符合目前所認知的ABCDE model。此差異有可能是昆欄樹的花部器官決定性基因調控模式的確和模式植物的調控機制不同，亦有可能是實驗技術上的限制所造成的差異。昆欄樹的花部器官發育機制尚待更進一步的研究。
並列摘要
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is very likely reduced during evolution instead of being a pleiomorph in the angiosperms, and the perianth has been replaced by the whole inflorescence as the attracting agent.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.
參考文獻
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