Prof. Thomas Laux

Contact Prof. Laux in Germany

Email: laux@biologie.uni-freiburg.de

For direct contact at SDAU

Dr. Yinghua Su

State Key Lab of Crop Biology

Room 602

Email: suyh@fenxiong.net

Tel: 0538-8249020

Starting July, a new research group will start at SDAU State Key Laboratory of Crop Biology, led by German professor Thomas Laux.

The group will focus on analyzing the regulation of stem cells in plants with the goal to develop agricultural applications that enhance breeding and adaptation to harsh conditions. Pluripotent stem cells can develop into any type of cell in an organism. In contrast to animals, plants can form completely new organs from their stem cells throughout their lives, which in the case of several species of trees may span a thousand years or more. Stem cell research promises to solve key problems in medicine and plant breeding.

We are searching for highly enthusiastic  new lab members at all levels (M.Sc., PhD, Postdoc) that are ambitious to work in a dynamic and supportive team, using cutting edge approaches and novel technologies.

For more details, please also visit our current Homepage at the University Freiburg   

Project 1:

Adaptation of root stem cells to environmental changes with a specific focus on the epigenetic regulation of stem cells.

Background:

Unlike most animals, plants can grow and form new organs throughout their life, which in the case of some long-lived trees can last for more than thousand year. The cells for this are supplied by pluripotent stem cells in the proliferative centers plants, the meristems. In addition to their longevity, plant growth and thus stem cell activity must adjust to environmental signals, such as season, light, water and nutrient supply. How active stem cells can be maintained for such a long time and accurately form new organs and how they can sense and adapt to environmental conditions is a central question for both, stem cell biology and agriculture.
Our group previously has shown that the stem cells of the shoot meristem are regulated by a local negatively feedback look between the transcription factor WUSCHEL (WUS) and the signaling peptide CLAVATA3 (Mayer at al, Cell 1998; Schoof et al, Cell 2000). We also found that the root meristem functions in a similar way, expressing the WUS homolog WOX5 (Sarkar et al., Nature 2007). WOX5 is required to maintain the stem cells forming the gravity sensing columella pluripotent but also can reprogram already differentiated cell to induced pluripotent stem cells (iPS). The way WOX5 work is that it changes the chromatin of the stem cells by recruiting a histone modifying enzyme to the DNA of its target genes, and as consequence, the Chromatin becomes compacted and the genes silenced (Pi et al., Developmental Cell, 2015). The columella stem cells are a prefect model to study stem cell regulation, because it consists only of three cells types, the niche cells, called quiescent center, that signal to maintain stem cells pluripotent, the dividing stem cells, and their differentiated daughter cells, the gravity sensing columella cells. The root stem cells must adapt to a number of abiotic and biotic environmental challenges including drought, flooding, nutrient shortage, soil contamination but also bacteria and fungus infections. Understanding how stem cells cope with these conditions to maintain root growth is not only of highest importance to stem cell biology, but also for agriculture, especially considering the global climate change.

Goal:

Understand how the genetic and epigenetic networks that regulates stem cells are affected and respond to environmental signals to cope with adverse conditions in Arabidopsis. Develop strategies how to use this knowledge to improve growth of cop plants on poor soil or dry conditions.

Methods:

In addition to standard genetic and molecular tools, the projects utilize a novel microfluidic technology that is developed together with our engineering partners. This set up allows to simulate environment conditions with simultaneous 3-dimensional live imaging of cells and of fluorescent reporter proteins. Transcriptome, chromatin, and live imaging data will be combined to create models of how regulatory networks of stem cells cope with changing environmental conditions. We will test the role of specific genes by creating CRISPR/CAS9 induced mutants and comparing how environmental adaptation changed compared to wild type.

(A) Diagram of the root stem cell niche (left). Stem cell are epigenetically regulated by the mobile transcription factor WOX5. For details see our publications: Pi et al., 2015, Dev Cell 33, 576; Sarkar et al., 2007, Nature 446,  811. (B) Microfluidic system to study adaptation of stem cell regulation to environmental conditions.

Project 2:

Formation of shoot meristem stem cell during embryogenesis.

Background

Whereas the function of stem cells for the regeneration of tissue or for growth has been studied in detail, much less is known so far about how stem cells form in the course of embryonic development. We recently published an article in the journal Developmental Cell presenting initial findings on how shoot stem cells in plants form during embryogenesis, the process of embryonic development. 

Several years ago, we discovered the transcription factor responsible for the continuous replacement of shoot stem cells in the model plant Arabidopsis. Called WUSCHEL, this protein is already present in the embryo when the stem cells form. Much to our surprise, our PhD student Zhongjuan Zhang made the key observation that it is not WUSCHEL but the related transcription factor WOX2 that is responsible for the development of the stem cells. All that was previously known about the protein WOX2 was that it controls earlier steps in the pattern formation of the embryo, the phase in which the embryo’s cells arrange themselves in a particular structure. Zhang discovered that WOX2 prevents the cells in the region of the embryo in which the stem cells form from differentiating into specialized cell types and thus from losing their unlimited potential for development.

This means that plants follow similar strategies in the process of stem cell development as found in animals. In the case of Arabidopsis, WOX2 regulates the balance between the two plant hormones cytokinin and auxin by allowing relatively large amounts of the former and relatively small amounts of the latter to collect in the progenitor cells of the stem cells. Plant researchers have already been using this mechanism for several decades to regenerate a shoot from a root or a leaf. This method, originally found in tissue cultures, therefore ultimately reflects the same mechanism that evolution already found much earlier to develop stem cells during embryogenesis.

Diagram of how WOX2 regulates the balance between auxin and cytokinin (CK) to establish shoot meristem (SAM) stem cell in the embryo. cot = cotyledons. See our publication Zhang et al. 2017,  Developmental Cell 40, 264–277.

Goal:

Understand how the network of transcription factors and hormones co-operate to establish stem cells in Arabidopsis. Develop strategies using this knowledge to improve plant regeneration of crop plants.

Methods:

In addition to standard genetic and molecular tools, the projects focuses on protein purification and protein interaction studies, including detection of protein complexes by high end microscopy. We will test the role of specific genes by creating CRISPR/CAS9 induced mutants.

Selected Publications Laux Laboratory

Zhang, Z., Tucker, E.,  Hermann, M, Laux, T. (2017). A molecular framework for the embryonic initiation of shoot meristem stem cells. Developmental Cell, 40, 264–277.

Pi, L., Aichinger, E., van der Graaff, E., Llavata-Peris, C., Weijers, D., Hennig, L., Groot, E., and Laux, T. (2015). Organizer-Derived WOX5 Signal Maintains Root Columella Stem Cells through Chromatin-Mediated Repression of CDF4 Expression. Developmental Cell 33, 576-88.

Forzani C, Aichinger E, Sornay E, Willemsen V, Laux T, Dewitte W, Murray JA. (2014) WOX5 suppresses CYCLIN D activity to establish quiescence at the center of the root stem cell niche. Curr Biol. 24, 1939-44.

Knauer, S., Holt, A. L., Rubio-Somoza, I., Tucker, E. J., Hinze, A., Pisch, M., Javelle, M., Timmermans, M. C., Tucker, M. R. and Laux, T. (2013). A Protodermal miR394 Signal Defines a Region of Stem Cell Competence in the Arabidopsis Shoot Meristem. Developmental Cell 24,125-132

Lieber, D., Lora, J., Schrempp, S., Lenhard, M., and Laux, T. (2011) Arabidopsis WIH1 and WIH2 genes act in the transition from somatic to reproductive cell fate. Current Biol.  21, 1009-1017

Ueda, M., Zhang, Z., and Laux, T. (2011). Transcriptional activation of Arabidopsis axis patterning genes WOX8/9 links zygote polarity to embryo development. Developmental Cell 20, 264-270.

Breuninger, H., Rikirsch, E., Hermann, M., Ueda, M., and Laux, T. (2008). Differential expression of WOX genes mediates apical-basal axis formation in the Arabidopsis embryo. Developmental Cell 14, 867-876.

Sarkar, A., Luijten, M., Miyashima, S., Lenhard, M., Hashimoto, T., Nakajima, K., Scheres, B., Heidstra, R. and Laux, T. (2007). Conserved factors regulate signaling in Arabidopsis shoot and root stem cell organizers. Nature 446, 811-814.

Laux, T. (2003) The Stem Cell Concept in Plants: A Matter of Debate. Cell 113, 281-283.

Lenhard, M., Bohnert, A., Jürgens, G. and Laux, T. (2001). Termination of stem cell maintenance in Arabidopsis floral meristems by interactions between WUSCHEL and AGAMOUS. Cell 105, 805-814.

Schoof, H., Lenhard, M., Haecker, A., Mayer, K.F.M., Jürgens, G., and Laux, T. (2000). The stem cell population of Arabidopsis shoot meristems is maintained by a regulatory loop between the CLAVATA and WUSCHEL genes. Cell 100, 635-644.

Mayer, K.F.X, Schoof, H., Haecker, A., Lenhard, M., Jürgens, G. and Laux, T. (1998). Role of WUSCHEL in regulating stem cell fate in the Arabidopsis shoot meristem. Cell 95, 805-815.