NCKU Research Team Unveils the Genome Sequence and Evolution of Orchids
成大團隊解開蘭花基因謎團,達爾文沒有遺憾
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        National Cheng Kung University (NCKU) Institute of Tropical Plant Sciences Associate Professor Wen-Chieh Tsai, Department of Life Sciences Associate Professor Song-Bin Chang and Orchid Research and Development Center Dr. Yu-Yun Hsiao jointly conducted an international study of the genome sequence of Apostasia shenzhenica (擬蘭). Their paper,“The Apostasia genome and the evolution of orchids”, has been published in Nature today.

        The team included 35 researchers from 17 research institutes in Taiwan, China, Belgium, and Japan. Among them are 6 from NCKU; Tsai is listed as the co-corresponding author, and Hsiao the joint first author.

        “Orchids carry special meanings for NCKU as well as the greater Tainan area in terms of research, culture and industry,” said NCKU President Huey-Jen Jenny Su in today’s press conference.

        Professor Tsai noted, “The team sequenced the Apostasia shenzhenica genome and annotated 21,841 protein-coding genes to solve the hundred-year-old puzzle of the orchid’s evolution.”

        There are about 30,000 species of orchids growing in almost every habitat except the north and south poles and extremely hot deserts. Among the extant orchids, Apostasia shenzhenica is one of the most primitive, and its morphological characters are quite different from others, providing a good example to demonstrate the genetic mechanisms of the orchid’s evolution.

        As the biggest family among flowering plants (approximately 10%), the orchid’s diversity has been an attractive topic of study for scientists since Darwin.

        “I never was more interested in any subject in my life, than in this of Orchids,” wrote Darwin to one of his friends.

        “Darwin’s quest for the evolution of orchids was fulfilled by our research team,” added President Su.

        Orchids have three sepals and three petals (of which one has specialized to form the labellum with different shapes and colors), stamens and pistil fused into a gynostemium, and pollens unified into pollinium on the stigma. With external pollination, they produce hundreds of thousands of seeds without endosperm. The seeds must intergrow with orchid mycorrhizal fungi for germinating.

        However, Apostasia shenzhenica has no specialized labellum, its pollens are powdery, and it is a terrestrial but not epiphytic orchid.

        The study of the genome sequence of Apostasia shenzhenica proves there was a whole-genome duplication of orchids. The comparative analyses show the changes within MADS-box gene classes during orchid evolution and the forming of specialized organs are the main causes of the extraordinary diversity of orchids.

        The team pointed out, “deciphering the genome sequence of Apostasia shenzhenica helps understand the orchid’s functional evolution and adapting process, and could be applied to precise breeding of orchids to cultivate new varieties adaptable to extreme climate.”

        Most orchids are insect-pollinated and symbiotic with fungi in nature and therefore, are important ecological indicator species.

        “Knowing the process of the orchid’s evolution and adaption also explores the ecological balance and provides data and references for environmental changes,” concluded the team.

        蘭花樣貌變化多端,其中奧秘,逾一世紀來科學家百思不解。成功大學與國際團隊合作,完成原始蘭花「擬蘭」全基因體解序,一舉解開蘭科植物演化之謎。成大團隊指出,基因體序列的解密,將被應用於蘭花精準育種,人們隨心所欲培育蘭花品種指日可待。這項突破性的研究 9 月 21 日榮登國際科研界排名第一的 Nature 期刊,並將台灣蘭花研究和產業推向另一個高峰。

        論文題名為「The Apostasia genome and the evolution of orchids(擬蘭基因體與蘭花演化)」,研究團隊指出,藉由分析比對現存最原始的蘭科植物之一「擬蘭」(Apostasia shenzhenica)與一般蘭花外觀特徵基因,證實MADS-box基因家族成員的保留與消失,是蘭科物種演化過程中形成多樣化的重要原因。該研究由成大熱帶植物科學究所副教授蔡文杰、蘭花研究中心助理研究員蕭郁芸,及生命科學系副教授張松彬等 6 人,協同中國、比利時、日本等國共17個研究單位共同參與。蔡文杰名列共同通訊作者,蕭郁芸則名列共同第一作者。

        成大團隊表示,精準育種除可改變花形,亦有助開發適應極端氣候的新品種。蘭花在大自然中需與真菌共生,是一個重要的生態指標,了解蘭花演化與適應的調控過程可了解生態之間的微妙平衡,為不可預期的環境變化提供更多的數據與參考。

        成大 21 日與外界分享研究成果。蘇慧貞校長表示,成大年輕團隊研究成果,登上國際科研界最重要的期刊 Nature, 對台灣的研究來說是重要的里程碑,對成大來說也具有多重義意,團隊成員都屬青壯世代,是成大生科系創系以來培育出的學者。此外,論文國外的合作學者,在日本擔任大學教授的一位成員,也是成大畢業校友,這在在顯示成大科學的能量與競爭力。而更讓人興奮的是,該研究讓達爾文多的年遺憾,得到完整解答。

        蘭花演化謎團的科學探究始於1862年,當時,達爾文收到一朵來自馬達加斯加島嶼奇特的蘭花(大慧星風蘭),花朵後方,竟然有長達30公分的細長花距,前所未來有構造,讓達爾文不斷思考,為什麼,提出一定有某種蛾類,口器伸長可超過 30 公分,如果這種蛾類消失,大慧風蘭也會滅絕的觀點; 直到1903年科學家才在馬達加斯加島發現一種口器展開長達 30 公分的天蛾。1992 年科學家終於記錄到這種天蛾拜訪大慧星風蘭,協助傳粉。

        蘭與天蛾共同演化外,少數蘭已轉變為鳥類傳粉,花距變短、寬度增加,以符合鳥嘴型狀,百年來科學家一直極欲探究蘭花演化出多樣性的奧秘。

        現今蘭科植物的特徵為,花瓣兩側對稱,下方一片不同形狀和色彩的花瓣(稱為唇瓣),中間一個蕊柱,頂端是花粉集結成團的花粉塊。另外,蘭花種子沒有胚乳,種子需與蘭菌共生才能發芽。科學界已知,MADS-box 家族基因調控蘭花的花萼、花瓣、唇瓣、蕊柱、花粉塊等花器官。

        擬蘭,雖是蘭科植物的一員,花的外表與一般蘭花大不相同,外觀無變形的花瓣(唇瓣)和完整的蕊柱,沒有花粉團塊而是顆粒,特別的是,擬蘭長於土壤,現在的蘭全是附生在其他植物或岩石上等。

        擬蘭全基因體解序後,團隊將其基因體數據,與一般蘭花做比對與分析,結果顯示,擬蘭雖無一般蘭科植物共同的明顯特徵(如唇瓣),但仍然有MADS-box基因家族,在花瓣、蕊柱、花萼、花粉等部位,都可見 MADS-box 基因家族調控的作用。證實蘭科植物為了生存,演化過程中MADS-box基因家族部份成員保留與消失,是物種多樣化的重要原因之一。

        少了 MADS-box 家族基因成員 B-AP3 與 E 群,擬蘭沒有特殊的唇瓣,也缺少完整的蕊柱。P 和 S-subclades 基因會調控花粉呈散開的顆粒狀,現今蘭花少了 P-subclades 基因,花粉集結成團塊。

        擬蘭的根只能在地下生長,而今的蘭花攀附到樹上或岩壁上,是因為有可以吸收空氣中養份與儲存水分的氣根,這是 MADS-box 家族中 AGL12 等基因的影響。擬蘭全基因體解序,揭開了蘭花演化之謎。