俄氏草花序分生組織基因CENTRORADIALIS於成花反轉的調控角色

Function of CENTRORADIALIS in Regulating Floral Reversion of Titanotrichum

吳培安(Pei-An Wu)

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(2016年)

https://doi.org/10.6342/NTU201601669

摘要

被子植物由營養生長到開花的轉換過程，受到環境訊息、發育、荷爾蒙等因素縝密地調控。然而，部分被子植物在身處不利於開花的條件時，會出現稱為「成花反轉」的現象，使得花分生組織逆轉為營養性或花序特性。在自然情形下，苦苣苔科的俄氏草（Titanotrichum oldhamii）在花季晚期會經歷成花反轉、產生營養性的珠芽繁殖體，行使無性生殖。過去的研究指出俄氏草的成花反轉與花分生組織特性基因FLORICAULA / LEAFY（FLO/LFY）表現量下降有關，本研究卻發現ToFLO除了主要在花分生組織表現，也在珠芽序生成位置表現，暗示ToFLO表現降低並非成花反轉的必要條件。另一方面，花序分生組織特性基因TERMINAL FLOWER 1 / CENTRORADIALIS（TFL1/CEN）在模式物種中曾被報導與成花反轉相關。藉由qPCR，我發現ToCEN在莖頂高量表現，與成花反轉及珠芽序形成有關；ToCEN的原位雜合訊號，則顯示ToCEN的表現位在花序分生組織的中心區域及珠芽序原基中。將ToCEN在阿拉伯芥中異位表現，不但延遲開花，還促進花序分支生長，花序結構與珠芽序的形態極為相似；轉殖株的花也發生成花反轉為葉化枝條、花萼包圍的次生花序、雌蕊著生花苞的退化花等。此外，在野生型阿拉伯芥嫁接至35S::ToCEN轉殖株的實驗中，能在接穗中偵測到ToCEN的RNA，顯示ToCEN可能透過訊息傳輸抑制花發育、促進成花反轉以影響花序結構。總結而言，本研究揭示ToCEN可能調控俄氏草的成花反轉及珠芽發育，且透過訊息傳遞促進花序延長、抑制花發育和延遲開花時間。此外，ToCEN在俄氏草中可能獲得了珠芽序發育的新功能，使俄氏草能夠以此行使獨特的無性繁殖、完成生活史。

關鍵字

成花反轉 ； 花序分生組織特性基因 ； CENTRORADIALIS ； 珠芽 ； 俄氏草

並列摘要

In angiosperms, the switch from vegetative growth to flowering is orchestrated by environmental signals, development, hormones, etc. However, few angiosperms go through “floral reversion”, floral meristems revert to vegetative or inflorescence identity, under conditions unfavorable for flowering. Naturally occurred Titanotrichum oldhamii (Gesneriaceae) reverting flowers to vegetative bulbils (propagules) in late flowering season for asexual reproduction. Previous studies suggested that floral reversion in Titanotrichum is related to floral meristem identity genes, FLORICAULA/LEAFY (FLO/LFY). In this study, however, ToFLO was found mainly expressed in typical floral meristem and the down-regulation expression of ToFLO during the initiation of bulbiliferous shoots suggest it may not be essential for floral reversion. In contrast, inflorescence meristem identity genes TERMINAL FLOWER 1/ CENTRORADIALIS (TFL1/CEN) were reported related to floral reversion in model plants. qPCR indicates the expression level of ToCEN is high in shoot apices, and this correlated to stages of floral reversion and initiation of bulbiliferous shoots. In situ hybridization signals of ToCEN demonstrate it was localized in central region of inflorescence meristem and bulbiliferous shoot primordia. Ectopic expression of ToCEN in Arabidopsis showed enhanced inflorescence architecture with extensive outgrowth of lateral shoot (coflorescence) branching, a phenotype greatly resembling bulbiliferous shoots, and delayed floral transition. Conversion of flowers into leaf‐like shoots, secondary inflorescence subtended by sepals and rudimentary flowers with buds on carpel are often found. In addition, in grafting of wild type Arabidopsis onto 35S::ToCEN stocks, I found that ToCEN RNA can be detected in grafted scions. This suggests ToCEN acts as transmissible signals to inhibit flower development and promote floral reversion to alter inflorescence architecture systematically. Together, this study revealed that ToCEN may regulate floral reversion and bulbil development of Titanotrichum, and also systematically functions in enhancing inflorescence outgrowth, inhibition of flower formation and delaying flowering time. ToCEN thus perhaps adopted a new role for bulbiliferous shoots formation in Titanotrichum, allowing it to incorporate this unique life history trait for asexual propagation.

並列關鍵字

Floral reversion ； inflorescence meristem identity ； CENTRORADIALIS ； bulbil ； Titanotrichum oldhamii

參考文獻

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