(ABOVE) A 3D computational simulation shows CLAVATA3 (CLV3) expression in a shoot apical meristem of Arabidopsis. The highest gradient is shown in red. (BELOW) The simulation is confirmed using confocal live imaging in an Arabidopsis shoot apical meristem, with the brightest purple signifying high CLV3 gradient.
West Lafayette, IN (August 2, 2018) – A Purdue University study has uncovered mechanisms that lead to stem cell formation and maintenance in plants. The findings may one day allow scientists to manipulate stem cell production to increase biomass that can be used for biofuels or grain yield in plants like corn and soybeans.
In findings reported August 2 in the journal Science, Yun Zhou, an assistant professor in the Department of Botany and Plant Pathology and the Purdue Center for Plant Biology, and co-authors from Purdue and the California Institute of Technology describe how plants create a pool of stem cells separate from their differentiated daughter cells in a meristem, and the daughter cells on the basal side of the meristem maintain the stem cells.
Undifferentiated stem cells are located in the meristems — the apex or tips of plant shoots and roots. These serve as a bank of blank cells that support plant growth and give rise to different organs such as leaves or flowers.
Zhou is investigating the ways in which plants initiate stem cell production and keep the stem cells activated.
“These stem cells keep dividing, and their daughter cells will eventually differentiate. But keeping up production of these stem cells is important for plant growth,” Zhou says. “If we can understand the mechanisms underlying the meristem development, we could have the potential to create a new biological tool to optimize crop growth.”
Zhou and colleagues show that this process is controlled by HAIRY MERISTEM (HAM) and WUSCHEL (WUS) genes.
In the stem cells, WUS activates the CLAVATA3 gene. In the basal differentiated cells, HAM and WUS together repress CLAVATA3, resulting in the specification of stem cells. The concentration gradient of HAM is also key for polarization, the initial split between stem cells and the basal differentiated cells.
“The balance is important. We found that if the concentration gradient of HAM is altered, the whole meristem identity is changed and the activity is reduced,” Zhou said. “Changes can lead to the ability to keep stem cells in an undifferentiated status.”
The team’s hypothesis for the project was built from a 3D computational model that simulates gene expression patterns in the meristem that control stem cell identity. That hypothesis was confirmed through experiments on the model plant Arabidopsis.
Zhou and colleagues will continue to improve their model to quantitatively predict stem cell activities in response to changes in gene expression. That knowledge will contribute to developing methods for controlling stem cells to improve crop growth and yield.
The research in Zhou’s group was supported by Purdue University, and work at the California Institute of Technology was supported by the National Institutes of Health, the Howard Hughes Medical Institute, and the Gordon and Betty Moore Foundation.
ABSTRACT HAIRY MERISTEM with WUSCHEL confines CLAVATA3 expression to the outer apical meristem layers
Yun Zhou1,2,3, An Yan1,4, Han Han2,3, Ting Li1,4, Yuan Geng2,3, Xing Liu1,3,5, Elliot M. Meyerowitz1,4
The control of the location and activity of stem cells depends on spatial regulation of gene activities in the stem cell niche. Using computational and experimental approaches, we have tested and found support for a hypothesis for gene interactions that specify the Arabidopsis apical stem cell population. The hypothesis explains how the WUSCHEL gene product, synthesized basally in the meristem, induces CLAVATA3-expressing stem cells in the meristem apex but, paradoxically, not in the basal domain where WUSCHEL itself is expressed. The answer involves the activity of the small family of HAIRY MERISTEM genes, which prevent the activation of CLAVATA3 and which are expressed basally in the shoot meristem.