Robust spatial patterning in a dynamic environment

• Applicant: Professorin Dr. Marja Timmermans
• Subject Area: Plant Cell and Developmental Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 539389005

Multicellular organisms rely on intricate developmental programmes for the proper formation and functioning of tissues and organs. Central to these programs are transcription factors (TFs). TFs form complex regulatory networks to generate precise spatial and temporal patterns of gene expression that instruct cells to adopt specific fates and functions. Many TFs with major contributions to development have been identified and fundamentals of TF action well described. However, a key question that forms the subject of this proposal remains: how do TFs establish robust developmental patterns of gene expression, particularly when the cell context changes continuously due to tissue growth. The study of adaxial-abaxial (top-bottom) leaf polarity in plants has emerged as an attractive experimental system to study developmental patterning. Polarity is crucial for forming flat leaves with distinct upper (adaxial) and lower (abaxial) surfaces optimized for light capture and gas exchange. Adaxial-abaxial polarity is specified through the interaction of a pre-pattern at the meristem periphery with the plant hormone auxin. This induces a localized transcriptional response that distinguishes adaxial from abaxial identity. To address the above question, we aim to determine how the dynamic patterns of adaxial-abaxial gene expression are organized at the growing vegetative shoot apical meristem, in space and time. What TFs ensure the position of the pre-pattern at the periphery of the growing meristem? What TFs drive the local transcriptional responses? The regulatory modules, despite being dynamic, must be robust, given that even small deviations in adaxial-abaxial patterning lead to widely diverse leaf shapes, often with adverse effects on fitness. We will apply a combination of targeted genetic methods, quantitative live cell imaging, and high throughput single cell resolution approaches to: 1) define cis-regulatory elements (CREs) controlling expression of polarity determinants at the meristem and during primordium development. 2) define the regulatory information contained within the CREs that shapes the precise spatiotemporal patterns of expression. 3) investigate the complex regulation of MIR166A, a key player in adaxial-abaxial polarity, and determine how the multiple TFs interact to control its spatial and temporal expression. The results will resolve the regulatory mechanisms behind adaxial-abaxial organ polarity. Of broader significance, they will show how developmental patterns arise and remain stable in dynamic environments.

• DFG Programme: Research Grants