| Summary: | 碩士 === 國立臺灣大學 === 生態學與演化生物學研究所 === 104 === 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.
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