Three-dimensional quantitative analysis of the Arabidopsis quiescent center.

Quiescent center (QC) cells represent an integral part of the root stem cell niche. They typically display a low division frequency that has been reported to be controlled by hormone signaling and different regulators, including the ERF115 transcription factor and D-type cyclins. Here, we applied a three-dimensional (3D) imaging pipeline to visualize the Arabidopsis QC cell number, volume and division patterns, including the visualization of anticlinal divisions that cannot be deduced from longitudinal 2D imaging. We found that five-day-old seedlings possess on average eight QC cells which are organized in a monolayered disk. In a period of seven days, half of the QC cells undergo anticlinal division in a largely invariant space. Ectopic expression of ERF115 and CYCD1;1 promote both anticlinal and periclinal QC cell divisions, the latter resulting in a dual-layered QC zone holding up to twofold more QC cells, compared to the wild type. Contrary, application of cytokinin or ethylene results in an increase in the number of periclinal but a decrease in anticlinal QC divisions, suggesting that they control the orientation of QC cell division. Our data illustrate the power of 3D visualization in revealing unexpected QC characteristics.