Abstract：
The bilateral-to-radial symmetry transition occurring during the development of the Arabidopsis thaliana female reproductive organ (gynoecium) is a crucial biological process linked to plant fertilization and seed production. Despite its significance, the cellular mechanisms governing the establishment and breaking of radial symmetry at the gynoecium apex (style) remain unknown. To fill this gap, we employed quantitative confocal imaging coupled with MorphoGraphX analysis, in vivo and in vitro transcriptional experiments, and genetic analysis encompassing mutants in two bHLH transcription factors necessary and sufficient to promote transition to radial symmetry, SPATULA (SPT) and INDEHISCENT (IND). Here, we show that defects in style morphogenesis correlate with defects in cell-division orientation and rate. We showed that the SPT-mediated accumulation of auxin in the medial-apical cells undergoing symmetry transition is required to maintain cell-division-oriented perpendicular to the direction of organ growth (anticlinal, transversal cell division). In addition, SPT and IND promote the expression of specific core cell-cycle regulators, CYCLIN-D1;1 (CYC-D1;1) and CYC-D3;3, to support progression through the G1 phase of the cell cycle. This transcriptional regulation is repressed by auxin, thus forming an incoherent feed-forward loop mechanism. We propose that this mechanism fine-tunes cell division rate and orientation with the morphogenic signal provided by auxin, during patterning of radial symmetry at the style.
摘要：
拟南芥雌性生殖器官（gynoecium）发育过程中发生的双侧到径向对称过渡是与植物受精和种子生产有关的关键生物学过程。尽管意义重大,在雌蕊顶点（样式）处控制径向对称性的建立和破坏的细胞机制仍然未知。为了填补这个空白，我们采用定量共聚焦成像与MorphoGraphX分析，体内和体外转录实验，和遗传分析，包括两个bHLH转录因子中的突变体，这些转录因子必需且足以促进向径向对称的过渡，SPATULA(SPT)和残疾(IND)。这里,我们表明，风格形态发生的缺陷与细胞分裂方向和速率的缺陷有关。我们表明，SPT介导的生长素在经历对称过渡的中尖细胞中的积累是维持垂直于器官生长方向的细胞分裂方向所必需的（背斜，横向细胞分裂)。此外,SPT和IND促进特定核心细胞周期调节因子的表达，细胞周期蛋白D1;1(CYC-D1;1)和CYC-D3;3,支持细胞周期G1期进展。这种转录调节被生长素抑制，从而形成一个不相干的前馈回路机制。我们建议该机制通过生长素提供的形态发生信号微调细胞分裂速率和方向，在样式的径向对称图案期间。
