Frontier Leader Seminar - Integrated molecular circuits for stem cell activity in Arabidopsis roots

Frontier Leader Seminar

Title: Integrated molecular circuits for stem cell activity in Arabidopsis roots

Speaker: Ben Scheres

Affiliation: Wageningen University, NL

Abstract:

Multicellular control circuits can conveniently be studied in plants. Plant stem cells reside in niches and are maintained by short-range signals emanating from organizing centres. The Arabidopsis PLETHORA genes encode transcription factors required for root stem cell specification1,2. PLT expression is induced by the small plant hormone auxin. The PLT gene clade regulates expression of the PIN facilitators of polar auxin transport, which contributes to a specific auxin transport route that maintains stem cells at the appropriate position3. PLT proteins and auxin also cooperate to control asymmetric cell divisions in stem cells4. We address the properties of the PLT-PIN feedback loop by gene and protein network analysis and computational modelling.

Stem cells and their daughters in the root display specific asymmetric divisions at fixed locations. We investigate how such divisions are spatially regulated. The SHORTROOT-SCARECROW transcription factor pathway provides mitotic potential to the stem cell daughters that form the proximal meristem. This activity involves the conserved RETINOBLASTOMA-RELATED (RBR) pocket protein5, and we have established molecular links between the RBR pathway and SCR action that form a feedback control system. Formal analysis of this feedback circuit indicates that it acts as a bistable switch ensuring asymmetric divisions at fixed positions6. Our work illustrates how divisions that shape tissues are robustly positioned by dynamic regulatory circuits combining intracellular and extracellular loops.

1. Aida M. et al. (2004). Cell 119, 109-120.
2. Galinha,C.et al (2007). Nature 449, 1053-1057.
3. Grieneisen,V.et al (2007). Nature 449, 1008-1013.
4. Dhonukshe, P. et al (2012). Cell 149: 383-396.
5. Wildwater, M.et al (2005). Cell 123, 1337-1349.
6. Cruz-Ramirez, A. et al (2012). Cell 150, 1002-1015.

Short biography:

Ben Scheres graduated in Plant Pathology at the University of Wageningen in 1982, where he also pursued PhD studies in the group of Ton Bisseling. After completing a PhD in plant-microbe interactions in 1990, Ben Scheres aimed to develop the Arabidopsis root as a model system appropriate for true multidisciplinary dissection of developmental mechanisms. In the early stages of his research career, he has defined anatomically, experimentally and genetically the root stem cell organization in Arabidopsis and was the first to show that the stem cell niche concept simultaneously developing in the animal field was applicable to the plant kingdom. His group was the first to reveal the concept of auxin accumulation in ‘maxima’ as a mechanism for pattern formation in plants – which is now broadly recognized as the key mechanism to regulate plant development. More recently, his group was the first one to discover that plant stem-cell specification factors act in gradients and that specification of the stem cell state uses quantitative inputs from such transcription factors.

Ben Scheres recently moved from the University of Utrecht where he was full professor of Plant Developmental Biology and directed the Biocomplexity and Bioinformatics Institute, to Wageningen University. He has published over 100 articles and received several honorary awards during his career including the prestigious Advanced Investigator Grant from the European Research Council in 2008.