https://scholars.lib.ntu.edu.tw/handle/123456789/140691
標題: | 真雙子葉植物基群花部B群基因之演化研究 | 作者: | 胡哲明 | 關鍵字: | 真雙子葉植物;B 群基因;基因重複;選汰限制;Eudicots;B-class gene;gene duplication;selective constraint | 公開日期: | 2004 | 出版社: | 臺北市:國立臺灣大學生態學與演化生物學研究所 | 摘要: | 雖然花部器官決定的ABC 模組解釋 了大部份被子植物花部特徵的形成,但在 被子植物基群以及真雙子葉基群的植物, 其花部器官決定的基因表現仍存在許多變 異。在真雙子葉植物基群及核心真雙子葉 植物的基群的花部大小以及花被片的輪數 都與典型核心真雙子葉植物有很明顯的差 異,比如昆欄樹的花被片缺失,而檀香目 植物的花被片通常只有一輪。顯然在此之 中必定在花部發育的調控中發生了一些未 知但重要的改變,因此這些植物在探討被 子植物花被片的演化上扮演著非常重要的 角色。近年來的研究顯示,在ABC 三群基 因在演化至核心真雙子葉植物的過程中各 發生了一次主要的基因重複事件。然而, 二個B群同源基因的系群只有其中之一在 此主要重複事件中固定下來, 而變成 euAP3 或TM6 次系群。因此,這樣的重複 事件可能與真雙子葉植物基群花部特徵的 多樣性有關。本計畫分別自演化上屬於關 鍵類群的黃楊科(臺灣黃楊)、昆欄樹科(昆 欄樹)、第倫桃科(第倫桃)以及檀香目植物 (百蕊草、椆樹桑寄生以及高氏桑寄生)中 選殖花部B 群同源基因,希望能釐清B 群 同源基因重複事件是否在真雙子葉植物基 群中發生。在六種植物中,一共得到17 個與B 群同源基因相似的cDNAs 序列。 譜系分析結果顯示, 前兩種植物具有 paleoAP3 同源基因,而後四種植物則具有 euAP3 或 TM6 同源基因。比較不同譜系分 析的結果後,本研究將B 群同源基因的重 複事件的發生時間推定於昆欄樹科出現之 後,核心真雙子葉植物分歧前的這段演化 期間。此外,選汰壓力偵測的結果亦顯示 PI-like 基因系群或是AP3-like 基因系群在 各演化階段均受到強烈的純化選汰 (purifying selection)壓力影響,尤其在被子 植物基群與真雙子葉植物基群之間,選汰 壓力的變動相當地顯著,但是基因重複與 選汰壓力在不同植物類群間的關連性,仍 有待進一步的釐清。 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. |
URI: | http://ntur.lib.ntu.edu.tw//handle/246246/10821 | 其他識別: | 922621B002022 | Rights: | 國立臺灣大學生態學與演化生物學研究所 |
顯示於: | 生態學與演化生物學研究所 |
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