Lay summary

Plant cells are surrounded by a rigid yet elastic extracellular matrix, the cell wall. This structure, characteristic for plant cells, has protective functions and at the same time restricts cell growth. Hence, cell wall expansion is a critical step during cell enlargement. While the composition of the cell wall has been analyzed extensively, it is still not well understood how plants regulate growth of the cell wall. In particular, the regulatory mechanisms that influence wall expansion processes and hence regulate wall growth remain poorly understood.

A major growth controller of eukaryotic cells in general is the TOR (Target of Rapamycin) pathway, a signaling network that senses environmental condition and growth factors and regulates growth processes accordingly. In mammals, targeting the TOR pathway via the cytotoxic drug rapamycin is being used to treat several conditions in humans. Recently, we have identified the TOR pathway as a regulator of cell wall development in Arabidopsis thaliana (thale cress). Interfering with the TOR pathway by rapamycin or by inactivating ROL5, a protein that is participating in the TOR network, induces changes in the cell wall structure. Plants with an inactive ROL5 protein (rol5 mutants) are not only affected in the TOR network but also fail to properly modify tRNAs, suggesting that the ROL5 protein influences several processes.

One aim of this project is to characterize the ROL5 protein in more detail. We have evidence that the ROL5 protein indeed has a dual function in the TOR network and in tRNA modification. We are currently investigating the possibility that ROL5 is interacting with different proteins that are affected in either tRNA modification or in the TOR network. Plant affected in the genes encoding these proteins will be characterized for changes in cell wall structures.

In a second part of this project, we are investigating the role of flavonols on plant development. Flavonols are secondary metabolites, can influence diverse cellular processes and thus have health-beneficial effects in humans. Yet, their mode of action in plants remains largely elusive. We have established plant lines (again Arabidopsis thaliana) that show changes in the flavonol accumulation pattern, which induces aberrant cell development. Through a genetic approach, we were able to identify several cellular processes that seem to be under the influence of flavonols. These findings will be analyzed in more detail in order to shed light on the function of flavonols during plant development.