Cell Biology & Molecular Genetics

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Subject: search.filters.subject.AGAMOUS

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    Distinct double flower varieties in Camellia japonica exhibit both expansion and contraction of C-class gene expression
    (Springer Nature, 2014-10-25) Sun, Yingkun; Fan, Zhengqi; Li, Xinlei; Liu, Zhongchi; Li, Jiyuan; Yin, Hengfu
    Double flower domestication is of great value in ornamental plants and presents an excellent system to study the mechanism of morphological alterations by human selection. The classic ABC model provides a genetic framework underlying the control of floral organ identity and organogenesis from which key regulators have been identified and evaluated in many plant species. Recent molecular studies have underscored the importance of C-class homeotic genes, whose functional attenuation contributed to the floral diversity in various species. Cultivated Camellia japonica L. possesses several types of double flowers, however the molecular mechanism underlying their floral morphological diversification remains unclear. In this study, we cloned the C-class orthologous gene CjAG in C. japonica. We analyzed the expression patterns of CjAG in wild C. japonica, and performed ectopic expression in Arabidopsis. These results revealed that CjAG shared conserved C-class function that controls stamen and carpel development. Further we analyzed the expression pattern of CjAG in two different C. japonica double-flower varieties, `Shibaxueshi’ and `Jinpanlizhi’, and showed that expression of CjAG was highly contracted in `Shibaxueshi’ but expanded in inner petals of `Jinpanlizhi’. Moreover, detailed expression analyses of B- and C-class genes have uncovered differential patterns of B-class genes in the inner organs of `Jinpanlizhi’. These results demonstrated that the contraction and expansion of CjAG expression were associated with the formation of different types of double flowers. Our studies have manifested two different trajectories of double flower domestication regarding the C-class gene expression in C. japonica.
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    LARSON directly represses AGAMOUS during early flower organogenesis in Arabidopsis thaliana
    (2004-04-30) Bao, Xiaozhong; Liu, Zhongchi; Cell Biology & Molecular Genetics
    How cells in a multicellular organism assume their developmental fates and form distinct patterns is a fundamental biological question. To address this question, I studied genetic and molecular regulation of Arabidopsis flower organ formation and identity determination. Specifically, how the expression of floral meristem and floral organ identity gene AGAMOUS (AG) was regionalized during flower organogenesis. A novel AG repressor LARSON (LSN) was previously isolated in a genetic screen. lsn loss-of-function mutations caused precocious expression of AG in the inflorescence meristem and ectopic expression of AG in sepal primordia, resulting in partial homeotic transfomation of late inflorescences into floral meristems and strong homeotic transformation of first whorl sepals into carpels. LSN encoded a homeodomain protein that directly bond to AG cis-regulatory elements in vitro. The cis-regulatory elements were conserved in 17 Brassicaceae species. LSN was expressed in a subset of cells located in the peripheral zones of inflorescence and floral meristems. LSN expression was significantly reduced in the sepal and petal primordia in wild-type flowers, indicating that repression of AG in the sepals and petals was independent of LSN transcription. LSN might establish epigenetic AG repression in the ancestral cells in the peripheral zone to specify the identities of descendant cell types in the floral organs. Therefore, floral organ identities were not only dependent upon gene expression in the organs, but were also dependent upon the histories of the cell development. Genetic and molecular analyses showed that LSN acted upstream of a putative repression complex, which, I proposed, was involved in the maintenance of AG repression in flowers. The putative repressive complex consistes of APETALA1 (AP1), LUNIG (LUG) and SEUSS (SEU) known to encode flower specific repressors of AG. Mutations in these three genes enhanced the lsn phenotypes. However, none of their proteins interacted with LSN in yeast. Instead, AP1, SEU, and LUG might form a protein complex. Genetic and molecular analyses suggested that the AG-repressive functions of the putative complex depended upon LSN activity in the peripheral zone of floral meristem. The AG-repressive function of LSN in the inflorescence meristem was independent of AP1/SEU/LUG putative complex.