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Report

Teaser, summary, work performed and final results

Periodic Reporting for period 3 - PROCELLDEATH (Unraveling the regulatory network of developmental programmed cell death in plants)

Teaser

Summary

Programmed cell death (PCD) is a fundamental biological process that actively terminates a cellâ€™s vital functions by a well-ordered sequence of events. In both animals and plants, various types of PCD are crucial for development, health, and the responses to various stresses. Despite their importance, only little is known about PCD processes and their molecular control in plants. Still, an intricate regulatory network must exist that renders specific plant cell types competent to initiate and execute PCD at precisely determined developmental stages.
I recently established a powerful developmental PCD model system in Arabidopsis thaliana, based on a PCD process occurring during root cap development. This root cap model has the potential to revolutionize existing concepts of plant PCD, as it combines a precisely predictable PCD process in easily accessible cells on the root periphery with the abundance of resources available for Arabidopsis research. Exploiting the root cap system will enable me to tackle unresolved fundamental questions about the regulation of developmental PCD in plants: How do cells acquire PCD competency during differentiation? Which signals trigger PCD execution at just the right moment? What are the actual mechanisms that disrupt the vital functions of a plant cell? I will obtain answers to these questions through a comprehensive strategy combining complementary approaches, taking advantage of cell-type specific transcriptomics, forward and reverse genetics, advanced live-cell imaging, biochemistry, and computational modeling.
Our unpublished data point to the existence of a common core mechanism controlling PCD not only in the root cap, but also in other vital organs including the vasculature, anthers, or developing seeds. Thus, this project will not only be significant to advance our knowledge on PCD as a general developmental mechanism in plants, but also to generate new leads to tap the so far underexploited potential of PCD in agriculture.

Work performed

\"The work performed is listed in detail in the attached file \"\"PR_CORE_SCIENTIFIC_1.pdf\"\". As I regard the work performed and the main results as confidential, I do not want to repeat them here.\"

Final results

In recent years, developmentally controlled programmed cell death (dPCD) in plants has been investigated in various tissues, developmental contexts, and plant species. Though various details concerning cell physiological and cell biological processes occurring during dPCD have been described, and several important dPCD regulators have been identified, we are to date still far from a comprehensive, systems-biology level understanding of dPCD in plants.
Many PCD processes that occur during plant development take place within complex tissues, for instance inside the anther, the vascular bundles, or the developing seed. These tissues are inherently difficult to target with pharmacological means, and challenging for high-resolution and live-cell imaging during PCD.
To overcome this limitation, various cell culture systems have been established. However, although the PCD processes in these systems can be reliably induced by gene expression, peptide-, or hormone-treatments, the developmental context of the surrounding plant tissues is missing. Putative communication processes with neighboring cells, for instance, are difficult to address with these cell culture-based systems.
Finally, dPCD processes in which cell death occurs within the organ context, but still accessible for pharmacological treatments and imaging, have been described. Most of these processes, however, are investigated in plant species which are difficult to transform, have complex or unsequenced genomes, or both, for instance in lace plant, Scots pine, or field poppy.
With the Arabidopsis lateral root cap (LRC) dPCD model system I want to overcome some of the limitations that have been encountered in diverse model systems. The LRC offers a unique combination of features:
1. PCD takes place in planta and in situ, within the developmental context of the growing root tip
2. PCD of individual cells is precisely predictable and traceable in space and time
3. PCD processes are amenable to pharmacological manipulation and advanced live-cell imaging
4. LRC PCD occurs in Arabidopsis thaliana, by far the most advanced plant model system available
Another innovative aspect of the proposed research is the combination of developmental genetics and advanced imaging techniques in the context of dPCD. As apoptosis in animals, dPCD in the LRC is a fast process followed by rapid clearance of the cellular contents, making it difficult to detect or visualize. I will counter these challenges with cutting-edge imaging approaches. Finally, computational modelling will be applied for the first time to simulate the intricate four-dimensional pattern of LRC differentiation and PCD in the context of the growing root tip, which has been not achieved so far. This interdisciplinary approach will be a challenging task. However, in collaboration with the research team of an internationally recognized experts at the MPI in Cologne I am confident that we will be able to combine wet lab experiments and computational modelling to decisively advance our understanding of LRC PCD processes and their impact on plant organ development.

Results from the proposed project on root cap PCD will make a considerable contribution not only to the plant PCD field, but also to the field of root and plant development in general. For instance, the integration of PCD in the root cap differentiation program, and the tight link between LRC and meristem size are important to correctly interpret different aspects of root growth and development.
Concerning PCD regulation, I will contribute to the understanding of PCD as integral part of plant development by identifying major nodes and edges of the molecular network that connects the control of tissue differentiation with PCD regulation. Further, I will have gained first insights into the signaling processes controlling the precise onset of LRC PCD. Several novel key regulators and executers of LRC PCD will be identified, some of which might be sparking entirely novel r