紫金牛屬植物系統分類與其內共生細菌之演化

Systematics and evolution of Ardisia (Primulaceae), with notes on their endosymbiont, Burkholderia (Burkholderiaceae)

楊承瑞(Chen-Jui Yang)

指導教授 ： 胡哲明

國立臺灣大學/生命科學院/生態學與演化生物學研究所/博士(2022年)

https://doi.org/10.6342/NTU202200491

摘要

紫金牛屬植物(報春花科、紫金牛亞科)有超過700個被接受的物種，主要分布於熱帶和亞熱帶地區，於東南亞和美洲地區的多樣性最高。目前對於紫金牛屬的定義並不明確，且本屬植物經常和相近屬混淆。在紫金牛屬圓齒紫金牛亞屬植物中發現有和伯克氏菌形成葉瘤共生的現象，其共生菌為垂直傳遞且具高度專一性和宿主依賴性，暗示著二者可能有共同種化的演化歷史。本論文之研究重點為紫金牛屬植物之譜系分類，以及共生現象在屬內的演化關係。
本論文主要使用亞洲的紫金牛屬植物和其近緣物種作為材料進行分子譜系研究。結果發現紫金牛屬並非單系群，且至少有另外四個屬的植物被包含於紫金牛屬支序中，四個屬分別為管金牛屬、管藥金牛屬、島金牛屬和環蕊金牛屬；此結果顯示紫金牛亞科中屬的界限應該被重新訂正。另外，紫金牛屬下的分類系統僅有部分為單系群，部分亞屬的分類定位應被重新檢視。
本研究定序了Ardisia pusilla和Labisia pumila之葉綠體基因體，並加入其餘已知的本屬及其近緣群之完整葉綠體基因體進行比較基因體學研究。結果發現紫金牛屬和其近緣群之葉綠體基因體的結構、序列長度、GC含量、密碼子使用頻率等特徵均高度保守。利用完整葉綠體基因體序列進行譜系分析的結果顯示紫金牛支序中屬、亞屬和種的關係均有高度解析力。另外，本研究亦辨識出三個高度變異的葉綠體片段，可能為對於紫金牛和其近緣群具有高度解析力的分子標記。
綜合紫牛金屬譜系分析結果，以及利用共譜系分析和拓撲學測試檢視具有葉瘤的紫金牛屬植物和其共生的伯克氏菌的演化關係，結果發現紫金牛屬植物宿主和其共生的伯克氏菌的譜系關係不具有嚴格的對應關係而僅是大致上相同，顯示雖然共同種化為主要的演化事件，但宿主轉移事件亦偶爾發生。

關鍵字

分類學 ； 伯克氏菌 ； 報春花科 ； 紫金牛科 ； 紫金牛屬 ； 葉綠體基因體 ； 葉瘤共生現象

並列摘要

The genus Ardisia (Myrsinoideae, Primulaceae), with over 700 accepted species, is mainly distributed in the tropical to subtropical areas, especially diverse in the Southeast Asia and the Americas. The current circumscription of Ardisia is not clear and often confused with some relatives. The leaf nodule symbiosis has been found between the species of Ardisia subgenus Crispardisia and their symiotic Burkholderia species. The symbionts are vertically transmitted, highly specific, and highly dependent on the hosts, suggesting strict cospeciation may have occurred in the evolutionary history. The main foci of this dissertation are to conduct phylogenetic reconstruction of the genus Ardisia and examine the evolutionary history of endosymbiosis in the genus.
A phylogenetic analysis, focusing on the Asian Ardisia species and allies, was conducted. The results showed that Ardisia is not a monophyletic group, and at leat four genera, Sardiria, Hymenandra, Badula, and Oncostemum, are nested within the Ardisia clade. The results suggest that the generic limits within Myrsinoideae (Primulaceae) need to be further revised. The infrageneric classification of Ardisia was partly supported as monophyletic, and several subgenera need further revision.
For the first time, two complete plastomes, Ardisia pusilla and Labisia pumila, were sequenced and comparatively analyzed with other available complete plastomes of Ardisia species and allies. The results showed that the plastomes of Ardisia species and allies are highly conserved in structure, sequence length, guanine-cytosine content, and codon usage. Phylogenetic analysis using the whole plastomes showed high resolution at the generic, subgeneric, and species levels withing the Ardisia clade. In addition, three highly variable regions (rpl36-infA-rps8, rpl22-rps19, and ycf1) were identified as potential molecular markers with high discriminatory power across Ardisia species and allies.
The topology tests and cophylogenetic analyses were conducted to explore the evolutionary history of leaf-nodulated Ardisia species and their symbiotic Burkholderia species. The results showed a general concordance between the Ardisia hosts and their Burkholderia symbionts rather than a strict cophylogenetic relationship. The results suggest that cospeciation events occurred at most time in their evolutionary history, while host-switching events may occur sometimes.

並列關鍵字

Ardisia ； Burkholderia ； leaf nodule symbiosis ； Myrsinaceae ； plastome ； Primulaceae ； taxonomy

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