馴化種非洲菫花部反轉輻射對稱性狀的分子發育機制探討

The Role of Floral Symmetry Genes on Actinomorphic Reversion in Domesticated Saintpaulia ionantha

張詠嬋(Yung-Chan Chang)

指導教授 ： 王俊能

國立臺灣大學/生命科學院/生態學與演化生物學研究所/碩士(2009年)

https://doi.org/10.6342/NTU.2009.02449

摘要

相較於輻射對稱花，兩側對稱花常具專一傳粉者並有較高的授粉效率，故其種化速度亦常較前者來得快。然而，苦苣苔科(Gesneriaceae)的野生型園藝植物非洲菫(Saintpaulia ionantha, African violet)原本野生型(wild type)的花是兩側對稱，但在人擇栽培後有反轉為輻射對稱的變異型(peloria)出現，這給予我絕佳機會探討在同一種植物中花部對稱性轉換的分子機制。前人研究顯示，在金魚草(Antirrhinum majus)中，由於CYCLOIDEA (CYC) 和DICHTOMA (DICH) 只在背側花瓣(dorsal petal)上表現，並共同促進下游基因RADIALIS (RAD)活化。再加上RAD與腹側花瓣促進基因DIVARICATA (DIV) 相互拮抗，而使DIV無法作用在背側花瓣，最後促成金魚草成為兩側對稱花型。在非洲堇中找到同源基因SiCYC、SiRAD、SiDIV，藉由RT-PCR比較檢測野生型(兩側對稱型)及變異型(輻射對稱型)各組織間的基因表現差異，探討非洲堇花對稱性狀改變的機轉。結果顯示，SiCYC1A和SiCYC1B在兩種對稱性狀中的背側花瓣上都有表現。然而，野生型和變異型的五片花瓣在早期花苞都可偵測到SiCYC1A和SiCYC1B的高表現量，但到了開花晚期時兩者的表現量都幾乎偵測不到。相對的，SiDIV在野生型和變異型的早期花苞時期所有花瓣上的表現量都很高，但到了開花晚期時變異型仍有殘餘的SiDIV表現，野生型卻已偵測不到。綜此推測，變異型的花發育成輻射對稱可能是由於開花晚期時SiCYC表現量下降及SiDIV持續表現，造成花發育後期兩側對稱性的無法繼續維持，而成了輻射對稱花形式(腹側化影響)。另外，SiCYC在兩種對稱型的背側花瓣上都有表現，可以從輻射對稱變異型花朵中背側及兩側雄蕊略小於腹側雄蕊的形態觀察中找到佐證，顯示變異型花朵仍有殘存的兩側對稱性存在。本研究首次報導不僅對稱基因表現位置，甚至時間也是關鍵性因素，因而促成殘存兩側對稱的變異型輻射對稱花的形成。

關鍵字

非洲堇 ； 兩側對稱 ； 輻射對稱 ； CYC ； RAD ； DIV

並列摘要

Flower symmetry switching from actinomorphy to zygomorphy is an important evolution trait in angiosperm. Zygomorphic flowering species often attract specific pollinators with greater pollination efficiency, therefore, these species usually have higher speciation rate. However, among zygomorphic Gesneriaceae species, some species have evolved from zygomorphy back to actinomorphy. In Saintpaulia ionantha (African violet, Gesneriaceae), actinomorphic peloria was raised in domesticated cultivation from the zygomorphic wild type. By comparing flower development between zygomorphic wild type and actinomorphic peloric type, the genetic differences can be identified. In model plant, Antirrhinum majus, CYCLOIDEA (CYC) and DICHOTOMA (DICH) have been shown expressed in dorsal petals and co-activate RADIALIS (RAD). On the other hand, DIVARICATA (DIV) expresses in ventral petals and antagonize with RAD to generate zygomorphy. Expression patterns of these Saintpaulia homologs (SiCYC, SiRAD, and SiDIV) thus were compared between flower buds of zygomorphic wild type and actinomorphic peloria. The results showed that, SiCYC1A and SiCYC1B were both detected in dorsal petals of wild type and peloria at early bud stage (3mm in diameter) but not in later stage (30 mm in diameter). On the other hand, SiDIV persists to express along late flowering stages in peloria but not in wild type. This suggests persistent expression of SiDIV and ceasing of SiCYC1A and SiCYC1B in late peloric flower stage may generate the actinomorphic flower (ventralized effect). Moreover, the expression of SiCYC in dorsal part of flowers in peloria may explain why the peloria retains traced zygomorphic syndrome (the dorsal and lateral stamens are smaller than the ventral ones). This is the first report that not only the differences of flower symmetry genes expression but also expression timings may result to zygomorphy/actinomorphy transition.

並列關鍵字

African violet ； zygomorphy ； actinormophy ； CYC ； RAD ； DIV

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