Research group Wolf
Plant cell wall signalling

Our research aims to decipher how signals from the plant’s extracellular matrix, the cell wall, are generated and perceived, and how this cell wall-mediated signalling intersects with the regulatory mechanisms of plant physiology and development. Cell walls encase every plant cell and tie neighbouring cells to each other, eliminating cell migration as a means for shape generation. Instead, cell walls control morphogenesis through selective and coordinated restriction of cell expansion. To control growth, but also to respond to environmental cues, the physical and chemical properties of the cell wall are under constant surveillance (Figure 1). We have discovered that information about the state of pectin, the most complex and dynamic cell wall component, is conveyed to intracellular signalling pathways that regulate growth and stress responses, but also the maintenance of cell identity. Focusing on cell fate patterning in meristems, we study how cell wall signalling affects cellular decision making. A particular emphasis of our work rests on the plasma membrane and its multitude of cell surface receptors as the interface between cell wall and the cell interior. We mainly use the reference plant Arabidopsis thaliana as a model system, but are also interested in cell wall biology in plants of the genus Miscanthus, widely regarded as one of the most promising bioenergy crops, to improve biomass valorisation and to unravel the transcriptional networks containing potential targets for cell wall optimization.

Understanding how cell wall signalling intersects with plant physiology and development

We have discovered a novel cell wall signalling pathway linking surveillance of the major cell wall component pectin to brassinosteroid (BR) signalling, a plant hormone pathway critically involved in growth control. Cell wall feedback-mediated activation of BR signalling hinges on RECEPTOR-LIKE PROTEIN 44 (RLP44), a member of the large family of LRR-type RLPs in Arabidopsis. RLP44 directly interacts with both the BR receptor BRI1 and its co-receptor BAK1 and acts as a scaffold to promote association of receptor and co-receptor. This interaction results in activation of the pathway at least partially independent of BR hormone availability and constitutes a novel mechanism of RLP action and LRR-RLK signalling activation. Hence, the cell wall, through RLP44, provides a lateral input into the well-known BR signalling pathway. Importantly, BR signalling exerts its signature effect, the promotion of cell elongation, mainly through the control of cell wall properties and, unsurprisingly, cell wall-related genes are highly over-represented among BR target genes. Hence, RLP44-mediated feedback signalling likely controls cell wall homeostasis, for example during cell wall expansion-mediated elongation growth. In agreement with this, disruption of this cell wall feedback results in loss of cell wall integrity and bursting of cells in the root elongation zone. Other pathways suggested to transduce signals from the cell wall have been described recently and it can be assumed that many more await discovery. Based on the findings described above, key questions in the lab relate to the mechanisms enabling perception of cell wall properties and how this feedback information is integrated with development. In addition, we hope to identify new cell wall signalling components underlying the communication between the cell intra- and the extracellular space, a fundamental theme for all organisms. As a developmental model, we use vascular development in the Arabidopsis root, in particular xylem specification and its adaptation to the environmental conditions.

Deciphering how the cell wall controls cell identity at the shoot apical meristem

Since plant cells are encased in cell walls and thus immotile, their individual fate-specification program is strongly dependent on the relative position within the organism. Positional information can be conveyed by gradients of diffusible factors or tissue mechanics, both of which act in part through the cell wall. Our research has indicated that cell wall signalling components are involved in the maintenance of cell fate, reminiscent of the regulatory role of the ECM in animals. We have selected the shoot apical meristem (SAM), which harbours the stem cell niche responsible for the generation of most above-ground plant organs as a model system to study the influence of cell wall properties on cell identity. We use quantitative imaging, omics approaches and cell type-specific, inducible CRISPR-Cas9 genome editing to decipher how feedback from the cell wall controls cell fate decisions at the SAM and expect these approaches to yield mechanistic insight into integration of intracellular and extracellular growth regulatory processes, opening new avenues to study how the immediate physical environment is able to guide cell fate decisions in plants.

Unravelling the regulation of cell wall biosynthesis and biomass generation in the bioenergy crop Miscanthus

Species of the genus Miscanthus are considered the most promising group of bioenergy crops, as they combine high biomass production with low input requirements. However, how secondary cell wall biosynthesis, the main driver of terrestrial biomass accumulation is regulated in Miscanthus is largely unknown. Of particular interest is the control of lignin quality, which is the key factor determining cell wall recalcitrance and thus the major constraint for the exploitation of lignocellulosic biomass as renewable resource for energy and bio-based products. It is noteworthy that attempts to alter cell wall recalcitrance genetically are often hampered by cell wall signalling-mediated compensatory responses resulting in significant reduction in biomass accumulation. We aim to identify key genes involved in secondary cell wall biosynthesis from Miscanthus and delineate the transcriptional programs regulating this process. Using RNA-seq analysis in combination with cell wall profiling, we found that individual members of a small MYB transcription factor family we isolated differ in their target spectrum of regulated genes, which is reflected in biotechnologically interesting differences in cell wall, particularly in lignin, quality In addition, we could identify specific motifs enriched in the regulatory sequences of the target genes of individual TFs, which will hopefully enable us to predict TF targets in the Miscanthus genome (Figure 4).