Abstract
The specified floral meristem will develop a pre-established number of floral organs and, thus, terminate the floral meristematic cells. The floral meristematic pool of cells is controlled, among some others, by WUSCHEL (WUS) and AGAMOUS (AG) transcription factors (TFs). Here, we demonstrate that the SCI1 (Stigma/style cell-cycle inhibitor 1) gene, a cell proliferation regulator, starts to be expressed since the floral meristem specification of Nicotiana tabacum and is expressed in all floral meristematic cells. Its expression is higher in the floral meristem and the organs being specified, and then it decreases from outside to inside whorls when the organs are differentiating. SCI1 is co-expressed with N. tabacum WUSCHEL (NtWUS) in the floral meristem and the whorl primordia at very early developmental stages. Later in development, SCI1 is co-expressed with NAG1 (N. tabacum AG) in the floral meristem and specialized tissues of the pistil. In silico analyses identified cis-regulatory elements for these TFs in the SCI1 genomic sequence. Yeast one-hybrid and electrophoresis mobility shift assay demonstrated that both TFs interact with the SCI1 promoter sequence. Additionally, the luciferase activity assay showed that NAG1 clearly activates SCI1 expression, while NtWUS could not do so. Taken together, our results suggest that during floral development, the spatiotemporal regulation of SCI1 by NtWUS and NAG1 may result in the maintenance or termination of proliferative cells in the floral meristem, respectively.
Highlights
The maintenance and termination of the floral meristem are orchestrated by a complex network of elements that involve transcription factors (TFs), hormonal signaling, and cell cycle control genes (Jha et al, 2020)
Our previous results have demonstrated that style cell-cycle inhibitor 1 (SCI1) regulates cell proliferation in pistils of N. tabacum (DePaoli et al, 2011)
WUS protein migrates from the organizing center (OC), where it is found at the highest level, into adjacent cells via cell–cell movement and activates CLV3 transcription (Yadav et al, 2011; Perales et al, 2016; Rodriguez et al, 2016)
Summary
The maintenance and termination of the floral meristem are orchestrated by a complex network of elements that involve transcription factors (TFs), hormonal signaling, and cell cycle control genes (Jha et al, 2020). WUS blocks cell differentiation by inactivating genes, such as the ARR7/ARR15 (ARABIDOPSIS RESPONSE REGULATOR) that are mediators of the auxin control of cytokinin signaling (Leibfried et al, 2005; Zhao et al, 2010). Another example is the role of WUS in inhibiting genes in the auxin biosynthesis pathway (Mano and Nemoto, 2012), preventing cell differentiation (Yadav et al, 2013). The interaction between these pathways guarantees the balance between proliferation and differentiation, which is essential for the correct formation of the flower (Sun et al, 2009)
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