Chromatin Architecture and Plant Development

Plant development is characterized by a remarkable flexibility in the control of growth rates and organ formation. These characteristics represent a major difference between plants and animals, which undergo pattern formation following a pre-determined morphogenetic blueprint. In contrast, during the entire life cycle (up to several hundred years) plant growth integrates genetic switches that control organ formation with a large spectrum of signaling pathways that sense and respond to variations in environmental parameters. These variations lead to modifications in morphogenetic programs, visible as adaptive growth responses in the course of a plant`s life cycle. A key role in the control of cell proliferation and differentiation processes has been attributed to the concerted impact of auxin and cytokinin, two phytohormones that act as principal regulators of organ initiation and subsequent differentiation. Specifically, the involvement of such phytohormone signals in the control of cell cycle progression was shown to play a central role in the regulation of plant cell proliferation and differentiation. In previous work we have identified PROPORZ1 (PRZ1, also known as AtADA2b), encoding a transcriptional co-activator protein representing part of a hypothetical Arabidopsis chromatin-remodeling complex involved in the regulation of phytohormone-mediated control of core cell cycle regulators. As a consequence, mutants deficient in PRZ1 are impaired in the control of auxin and/or cytokinin-induced growth responses. A further characterization of targets and of mechanisms, by which PRZ1 controls the impact of these phytohormones on chromatin architecture and cell proliferation, is subject of this proposal. The experimental plan includes a systemic, whole genome approach, intended to identify regulators of cell proliferation, and will make use of already characterized PRZ1 target gene(s), in order to study mechanisms by which the transcriptional co-activator influences chromatin architecture. Moreover, the role of PRZ1-interacting proteins will be analyzed in planta. In summary, these experiments are expected to provide essential information on mechanisms that control the adaptability of plant development via variations in chromatin architecture in response to an ever-changing environment.

Plant development is characterized by a remarkable flexibility in the control of growth rates and organ formation. These characteristics represent a major difference between plants and animals, which undergo pattern formation following a pre-determined morphogenetic blueprint. In contrast, during the entire life cycle (up to several thousand years) plant growth integrates genetic switches that control organ formation with a large spectrum of signaling pathways that sense and respond to variations in environmental parameters. These variations lead to modifications in morphogenetic programs, visible as adaptive growth responses in the course of a plant`s life cycle. A key role in the control of cell proliferation and differentiation processes has been attributed to the concerted impact of phytohormones that act as principal regulators of organ initiation and subsequent differentiation. This project analyzed the impact of the phytohormone auxin on chromatin structure and expression of key regulators of plant development in the model plant Arabidopsis thaliana. These experiments revealed reversible effects of auxin on histone modifications, which in turn are presumed to control the expression of a number of regulators of cell cycle progression. Moreover, proteins apparently required to mediate auxin signals on chromatin structure have been characterized in more detail in this project. Overall, the outcome of our experiments provides new insight into mechanisms that control the adaptability of plant development via variations in chromatin architecture in response to an ever-changing environment.