非洲菫 CYCLOIDEA 基因在花對稱性的遺傳調控

花演化出兩側對稱的型態促進花朵形狀變異，是開花植物重要的演化趨勢。苦苣苔科野生型的非洲菫為兩側對稱，由於人為喜好栽培出許多輻射對稱的園藝品系。因為此現象發生在同屬不同品系間，使得我們能在基因背景相似的狀況下探討花部對稱性的轉換機制是如何被人擇影響。野生型非洲菫擁有兩枚較小的背側花瓣、三枚較大的腹側花瓣；背側化輻射對稱品系(簡稱D品系)的五枚花瓣皆似野生型的背側花瓣；腹側化輻射對稱品系(簡稱V品系)的五枚花瓣則全為較大的腹側花瓣。本實驗室先前研究指出野生型非洲菫花部對稱性CYCLOIDEA基因SaCYCW侷限在背側花瓣表現，V品系SaCYCV在五枚花瓣只剩微量表現，而在D品系SaCYCD在五枚花瓣有大量表現，暗示著SaCYC在空間上的差異性表現可能是造成花部對稱性轉換的原因。本研究透過遺傳雜交試驗進一步關聯SaCYC等位基因與花部對稱形態間的關係，藉此探討SaCYC的空間差異性表現是否為順式調控(cis-regulation)，同時並藉由轉殖系統探討SaCYC基因於花部發育的功能，同時檢驗其在品系間有無功能上之分化。我們將野生型與V品系雜交後，其F1子代性狀全為兩側對稱，顯示野生型SaCYCW顯性於V品系SaCYCV；而野生型與D品系雜交之的F1子代中，兩側對稱與輻射對稱的性狀分離為1:1，推測D品系親本應為異型合子(SaCYCD/SaCYCW)，進一步發現F1子代的SaCYC與花型有著和親本一致的空間專一性表現。過量表現SaCYC1AW和SaCYC1AV於阿拉伯芥中發現兩者應無功能上之分化，皆使得阿拉伯芥有花瓣面積變小、葉片捲曲、側芽增加等性狀，顯示著SaCYC參與花部發育功能，且透過測量花瓣細胞大小得知應是透過抑制細胞分裂的形式。但是F1子代中SaCYC等位基因和花對稱表現型並沒有關聯。因此，我們推測SaCYC的確在花部對稱性發育的訊息傳遞路徑上扮演不可或缺的角色，而且可能是受上游某未知因子反式調控其空間差異性表現(trans-regulation)，進而引起品系間花部對稱性的轉變。另外，我們嘗試運用基因槍建立了非洲菫花瓣暫時性表現轉殖系統，得知在目標距離九公分和九百磅力每平方英寸的條件下有較佳的表現訊號。本研究報導了非洲菫SaCYC在花部對稱性發育上的功能以及其可能的遺傳調控機制。

關鍵字

花部對稱性；苦苣苔科；非洲菫； CYCLOIDEA ；遺傳雜交；基因轉殖

並列摘要

Floral bilateral symmetry (zygomorphy) is a major evolutionary trend in creating floral diversity. Wild-type African violet (Saintpaulia ionantha) flower is bilateral symmetry with two smaller dorsal petals and three larger ventral petals. The two radial symmetry cultivars, one with 5 dorsalized petals and the other one with 5 ventralized petals, have been artificially selected. Previous research indicated that CYCLOIDEA-like genes (SaCYCs) have been shown a dorsal-specific expression in the zygomorphic wild-type flower, while a reduced expression in the ventralized flower and an expanded expression in entire dorsalized flower, implying the alteration of the spatial expression pattern of SaCYCs might contribute to the transition of floral symmetry among cultivars. The aims, therefore, are to examine the genetic regulation on SaCYCs by analyzing the association between SaCYC allele and floral symmetry and understand the functions of SaCYC in floral symmetry development. Here, crossing between the zygomorphic wild-type and the ventralized cultivar gave all F1 zygomorphy, suggesting the wild-type is homozygous dominant (SaCYCW/SaCYCW), while the ventralized cultivar is homozygous recessive (SaCYCV/SaCYCV). Overexpression of SaCYC1AW and SaCYC1AV in Arabidopsis both showed smaller petals, curled leaves and dwarfism, suggesting coding regions of wild-type and ventralized alleles have similar functions on cell proliferation in floral development. On the other hand, crossing between zygomorphic wild-type and dorsalized cultivar segregated close to a 1:1 ratio in F1 on each parental type, suggesting the dorsalized cultivar is a heterozygote (SaCYCD/SaCYCW) and SaCYCD is dominant to SaCYCW. Although F1 hybrids with dorsalized actinomorphy all have entire flower SaCYC expression, their allelic combinations could be SaCYCD/SaCYCW or SaCYCW/SaCYCW. Surprisingly, those zygomorphic F1 individuals all have SaCYC specifically expressed at dorsal petals, but combinations of these alleles showed no difference as those of dorsalized actinomorphic F1s. This seems to rule out that the differences between cis-regulating elements (promoter regions) of zygomorphic wildtype and dorsalized cultivars are responsible for the variations of spatial SaCYC expression patterns during symmetry transition. To conclude, SaCYC does participate a crucial and indispensable role in the signal transduction pathway for floral symmetry development, but there might be an unidentified upstream factor(s) regulating the spatially specific pattern of SaCYC (trans-regulation), leading to floral symmetry transition among these three cultivars. In the future, using a biolistic bombardment to introduce SaCYC promoters of wildtype and dorsalized cultivars into petals of the actinomorphic cultivar with a GUS reporter transient assay can further support my conclusion. Preliminarily data was found that at target distance 9 cm and helium pressure 900 psi condition appeared better signals. Overall, this study is the first to suggest the unknown upstream controller of SaCYC is also an important missing link for regulating floral symmetry.

並列關鍵字

Floral symmetry ； African violet ； Gesneriaceae ； CYCLOIDEA ； gene inheritance ； genetic transformation

參考文獻

Almeida, J., Rocheta, M., & Galego, L. (1997). Genetic control of ﬂower shape in Antirrhinum majus. Development, 124, 1387-1392.

Broholm, S. K., Tahtiharju, S., Laitinen, R. A., Albert, V. A., Teeri, T. H., & Elomaa, P. (2008). A TCP domain transcription factor controls flower type specification along the radial axis of the Gerbera (Asteraceae) inflorescence. Proc Natl Acad Sci U S A, 105(26), 9117-9122. doi: 10.1073/pnas.0801359105

Busch, A., & Zachgo, S. (2007). Control of corolla monosymmetry in the Brassicaceae Iberis amara. Proc Natl Acad Sci U S A, 104(42), 16714-16719. doi: 10.1073/pnas.0705338104

Busch, A., & Zachgo, S. (2009). Flower symmetry evolution: towards understanding the abominable mystery of angiosperm radiation. Bioessays, 31(11), 1181-1190. doi: 10.1002/bies.200900081

Chapman, M. A., Tang, S., Draeger, D., Nambeesan, S., Shaffer, H., Barb, J. G., Knapp, S. J., Burke, J. M. (2012). Genetic analysis of floral symmetry in Van Gogh's sunflowers reveals independent recruitment of CYCLOIDEA genes in the Asteraceae. PLoS Genet, 8(3), e1002628. doi: 10.1371/journal.pgen.10026

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非洲菫 CYCLOIDEA 基因在花對稱性的遺傳調控

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