| Summary: | 碩士 === 國立臺灣大學 === 生命科學系 === 104 === Reproductive strategy, including sexual or asexual, which directly related to the maintenance of one species, is one of the most important issues of angiosperms. Titanotrichum oldhamii exhibits a unique reproductive strategy, which consists of floral reversion and pseudoviviparous bulbils formation. Previous study revealed that the inflorescence meristem identity gene ToCEN participates in bulbiliferous shoot formation, suggesting that bulbiliferous shoot and inflorescence may share certain homology. As the evo-devo theory proposes that novel morphogenesis are largely evolved by recruiting the pre-existed genes, whether there exists homologous regulatory toolkits between the two homologous structures ̶ the floral meristem and the bulbiliferous meristem ̶ in Titanotrichum is concerned in this study. The key regulatory toolkits for floral determinacy, namely the stem cell identity gene WUSCHEL (WUS) and its co-operator AGAMOUS (AG) are therefore chosen as the major candidates. Interestingly, unlike most of the species have only one WUS ortholog and one euAG ortholog, both genes are duplicated in Titanotrichum and displaying divergent expression patterns. While ToWUS1, ToAG1, and ToAG3 are mainly expressed in inflorescence, ToWUS2 and ToAG2 are dominantly expressed in bulbiliferous shoot. Though duplication of conserved toolkit is rare, it is usually followed by selection. This is also consistent with the results that ToWUS2 was positively selected, maybe for occupying certain regulatory niches that provide the indeterminate growth of bulbiliferous meristem. In case of Titanotrichum, this study presents the scenario that the duplicated stem cell identity genes ToWUS1 and ToWUS2 are involved in organogenesis of homologous sexual and asexual meristems respectively. And innovation on WUS-AG toolkit is closely linked to the novel morphogenesis, the bulbiliferous development, which contributes to the alternative reproductive strategy of Titanotrichum.
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