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.