Abstract
摘要:花部兩側對稱演化對於開花植物而言是一項重要的發育特徵,該特徵的演化可以增加開花植物花部的多樣性,因而促進快速種化。雖然兩側對稱花的物種被認為由輻射對稱花的物種演化而來,至今仍無詳盡的分子發育機制研究來了解野生植物花部對稱的遺傳調控。為了要了解花部型態呈現兩側對稱與輻射對稱的基因調控機制,我們在屬於苦苣苔科的大岩桐(Sinningia speciosa, Lamiales)找到了具有兩側對稱花(野生型)與輻射對稱花(突變型)的植株。野生型大岩桐所開的花呈現兩側對稱,然而在突變的大岩桐植株所開的花卻是輻射對稱,突變株的大岩桐提供一個相當好的研究機會,讓我們可以了解調控花部對稱性的基因機制。由於突變型的大岩桐花朵非常類似金魚草(Antirrhinum majus)CYCLOIDEA(CYC)基因的突變株的外表型。我們初步遺傳分析的研究結果顯示,將大岩桐野生型與突變株雜交後所產生的第一子代121株所開的花均為如同野生型的兩側對稱大岩桐,這表示兩側對稱性狀優勢於輻射對稱。我們也計畫將第一子代自交產生第二子代,在可預期會觀察到超過600株的第二子代中,也許會觀察到F2個體間,親本花部形態比例將會如孟德爾遺傳分離律預測出現3:1比例。當我們檢視大岩桐突變株親本SsCYC基因序列時,我們發現其SsCYC基因有一段16個核苷酸缺失現象造成蛋白質轉譯中斷現象。這顯示突變株的SsCYC基因缺陷可能就是使兩側對稱花反轉發育為輻射對稱花的關鍵。為了確認我們的假說,我們擬利用目標基因關聯分析檢查第二子代花部對稱外表型與CYC基因型的關聯,進而鑑別特定SsCYC基因型(野生型 vs. 突變型對偶基因)是否有促使兩側對稱花反轉發育為輻射對稱花的能力。為了更進一步查證SsCYC基因的功能,我們擬分別轉殖突變及野生型對偶基因至與大岩桐親緣最相近的模式植物茄科矮牽牛中(其花是輻射對稱)。藉由觀察轉殖後矮牽牛的花朵對稱性改變與否,我們將可確定ScCYC是否有改變花朵對稱性的功能。這項研究計畫將會是第一個結合遺傳及分子研究方法,共同來證實達爾文所觀察到的大岩桐花對稱性突變,可能僅是一個發育基因改變所造成的劇烈演化結果。同時,這些結果將可以使我們更進一步了解花部對稱性的發育遺傳調控,如何在不同被子植物類群被平行演化出來。
Abstract: The evolution of flower bilateral symmetry (zygomorphy) is a keynote developmental trait in angiosperm as it creates enormous floral diversity thus fastens the speciation rates and flower diversity. As zygomorphic species evolved from actinomorphic species, till now however, no detailed molecular developmental analysis has been studied to understand the genetic control of floral symmetry on natural species. The unusual reversal to actinomorphy flower form in Gloxinia (Sinningia speciosa, Lamiales), the so-called Darwin’s peloria, provide us a precious chance to study the genetic control and molecular basis of floral symmetry. The peloric Gloxinia has multiple petals (the wild type zygomorphic flower has 2 lobes on top and 3 on the bottom) strongly resembling the snapdragon (Antirrhinum majus) CYCLOIDEA (CYC) mutant phenotype. In our preliminary data, we crossed a peloric Gloxinia with its wild type and the 121 F1hybrid flowers were always like the zygomorphic wild type. The F2 generation with more than 600 individuals from two independent inbred lines, although still waiting for flowering, is expected to show perhaps a 3:1 segregation ratio on the floral symmetry trait in Mendelian inheritance. When examining the CYC genotype of peloric and wild type Gloxinia parents, the peloria appears to contain the mutated CYC homozygous alleles. Moreover, we found the F1hybrids were all CYC heterozygous (zygomorphy). This implies the mutated CYC allele in peloria is probably recessive and perhaps involved in Gloxinia flower reversal to actinomorphy. To confirm our hypothesis, we plan to examine floral symmetry segregation pattern among F2 individuals in morphological detail and correlate the floral type (zygomorphy vs. actinomorphy) to CYC genotype (normal allele vs. mutated allele). To further clarify the function of SsCYC, we will transform the normal and mutated allele into model plant petunia (actinomorphy, Solanaceae, Lamiales). The transformed flower phenotype shall testify whether or not SsCYC has putative function to alter flower symmetry. This shall be the first exciting study utilizing both genetic and molecular methods to provide evidence that Charles Darwin’s peloria could be a saltational effect mediated by floral symmetry genes. Our result shall facilitate greatly our understanding on the evolution of angiosperm flower bilateral symmetry in a developmental genetic content.
Keyword(s)
花部對稱性
發育演化
遺傳分離率分析
跳躍式演化
Flower symmetry
evo-devo
segregation analysis
RADIALIS
DIVARICATA
saltation