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Title: 石櫟屬物種生理生態性狀親緣訊息與蠟生合成基因正向天擇
Phylogenetic signal in eco-physiological traits and signature of positive selection in biosynthetic genes in stone oaks (Lithocarpus, Fagaceae)
Authors: 廖培鈞
Liao, Pei-Chun
Ho, Shao-Wei
Keywords: 功能性基因演化
functional gene evolution
phylogenetic signal
Issue Date: 2016
Abstract: 有些植物表皮細胞中的蠟生合成基因生合成蠟後,經通道蛋白運輸至細胞外堆疊,形成物理性屏障的結晶狀(epicuticular wax crystal)構造,常被認為與化學性防禦特徵(如:酚酸)之間有權衡關係。此外,葉表蠟有無的適應也可能反映在蠟生合成基因及受蠟影響的生態特徵上,如光合作用效率。本研究以石櫟屬物種作為材料,利用遺傳及生理生態分析探討葉表蠟結晶的有/無特徵是否為適應的結果。首先使用6個參考基因重建石櫟屬的親緣關係,發現距今約1400萬年前至800萬年前,至少出現3次獨立由無蠟到產生蠟結晶的特徵轉換的演化事件。在蠟骨架生合成(CER1、CER3)、調節性(CER7)、及運輸蛋白(CER5)等基因中,僅發現CER1在由無蠟到產生蠟結晶的特徵轉換時有正向天擇訊號;生理生態檢測中,蠟結晶均與酚酸及光合作用指數無顯著相關。但Y(II)及δ15N等光合作用指數在CER1基因樹呈現顯著的親緣訊息,顯示光合作用效率在種間的差異反應在蠟骨架合成的演化上。本研究推論,石櫟屬物種在中新世中期至上新世初期發生特徵轉換,當時劇烈的氣候變化也反映了蠟結晶生合成基因的正向天擇及光合作用效率上。
The epicuticular waxes are synthesized and transported by wax-related genes in plants. The wax crystals serve as defensive traits and are considered as a trade-off between physical and chemical traits e.g. phenolic acids. Besides, the leaf epicuticular wax may be related to photosynthetic efficiency. I select stone oaks (Lithocarpus, Fagaceae) as our research materials and obtain genetic and physiological data to investigate whether the presence/absences of leaf epicuticular wax is an adaptive trait in stone oaks. The phylogenetic relationship of stone oaks reconstructed by six reference genes showed that trait shifts at least three times from non-crystalized waxy into crystalized waxy epidermis since 140 Mya to 80Mya. I sequenced and tested positive selection signals in four wax-related genes, CER1, CER3, CER5, and CER7, which are categorized as two, backbone synthetic genes, one regulatory, and one transporter genes, respectively. Signature of positive selection on CER1 at three trait transitional events of non-crystalized wax to crystalized wax imply the adaptive feature of presence of leaf epicutucular wax in Lithocarpus. The eco-physiologic analysis showed that contents of phenolic acids and photosynthetic indices are not correlated with leaf epicuticular wax, but certain photosynthetic indices, Y(II), and δ15N showed significant phylogenetic signals associated with the CER1 gene tree. These results suggest the intraspecific differences of photosynthetic efficiency are response to the evolution of backbone gene. In conclusion, the trait shift events of leaf epicuticular wax in stone oaks that are inferred during the period of dramatic climate change during the Middle Miocene to Early Pliocene may be related to the positive selection of wax synthetic genes and associated with difference of photosynthetic efficiency between species.
Other Identifiers: G060143006S
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