RoL:Deciphering the robustness mechanisms of the stem promoting transcription factor gradient

Understanding how plants develop to optimize their size and shape is key to future efforts to improve plant performance under varying environmental conditions. Initial development takes place at a shoot apical meristem (SAM) comprising stem cells that will ultimately give rise to the rest of the plant body Remarkably, these stem cells divide throughout the plant's life span and provide cells for developing all above-ground plant parts, which form a sizable portion of the biomass that sustains life on earth.

Therefore, the study of the SAMs will impact future efforts to develop a sustainable agriculture that contributes to environmental protection. As in all multicellular systems, SAM development is a highly choreographed sequence of complex events and it is important to link mechanisms of growth across subcellular, cellular, tissue, and organismal levels.

To reach across these scales of inquiry, the project employ multidisciplinary approaches to develop experimentally supported multiscale mathematical models. These models will allow easy observation and manipulation of biological processes generating and testing new hypotheses on SAM development. The research involves a diverse group of students to engage in research and learn about the role of SAM function in plant development.

Importantly, these students will be trained in interdisciplinary thinking, which is critical to advance science into the future. The proposed outreach will help bring institutional resources to surrounding underserved communities through mentoring and engaging with undergraduate and high school students to learn about, experience, and potentially start down the road to careers in mathematical biology and related fields.

WUSCHEL transcription factor gradient regulation is critical in stem cell maintenance and SAM growth. Self-regulation of the WUSCHEL protein gradient involves simultaneous control of processes that occur at different spatiotemporal scales. The WUSCHEL gradient depends on the regulated diffusion of WUSCHEL into adjacent cells controlled through nuclear-cytoplasmic (N-C) partitioning by position-specific extrinsic signals such as CLAVATA3 (a peptide that activates receptor kinase signaling) and plant hormone-cytokinin signaling.

WUSCHEL, in turn, regulates CLAVATA3 through a unique concentration-dependent transcriptional switch. How transcriptional/post-translational control and spatial signals combine and achieve finely tuned regulation of the WUSCHEL gradient will be studied by utilizing a combination of experimental and computational methods. The experimental approaches will visualize the effects of transient system perturbations and derive parameters that will be fed into the computational model to provide a fine-grained determination of the influence of different system components.

The system will be examined on the level of a single cell and at the tissue level to study the control of WUSCHEL synthesis, sub-cellular partitioning, diffusion, and degradation regulated by the layer-specific signals (aim1). WUSCHEL concentration-dependent regulation of CLAVATA3 transcription will be explored in aim2. In aim3, a continuous signaling sub-model regulating the WUSCHEL protein accumulation will be integrated with the stochastic model of CLAVATA3 transcription.

This hybrid model will be used to understand the mechanisms regulating the robustness of the WUSCHEL gradient. The scalable hybrid model could be used broadly in the quantitative analysis of systems governed by events that occur in multiple spatiotemporal scales.

This Rules of Life award is co-funded by the Plant, Fungal and Microbial Developmental Mechanisms Program in the Division of Integrative Organismal Systems and the Cellular Dynamics and Function Program and the Genetics Mechanisms Program in the Division of Molecular and Cellular Biosciences.

This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.