From small molecule to gene: using chemical genetics to understand cell wall sensing and advance molecular resources

The cell wall of plants is a complex extracellular matrix of polymers and proteins that regulate cell shape and morphogenesis. Plant cell walls form an integral barrier to pathogen attack, they constrain the internal turgor pressure of the cell, control the movement of cell to cell metabolites and regulate of cell to cell adhesion. Animal cells completely lack a cell wall and this kingdom level divergence is an intriguing feature of cellular life. The presence of a cell wall is common to plants, algae, bacteria and fungi, but each kingdom level split displays a markedly different composition. We are interested in how the plant cell communicates and coordinates extracellular and intracellular events in the development of the polyalaminate cell wall. To drive us towards this goal we have developed a small molecule probe named quinoxyphen and used genetic mapping to clone its resistance locus named aegeus (ags). AEGEUS is a serine/threonine protein kinase associated with the cell wall and our studies suggest that quinoxyphen appears to be a chemical agonist of its functionality. Resistance is conferred by a point mutation within the putative extracellular oligosaccharide (pectin) binding domain resulting in phenotypes such as aberrant root hair morphogenesis, altered cell wall structure and response to sucrose and isoxaben. Our primary goal is to illuminate the significance of the AEGEUS mediated signal transduction by (physically and genetically) mapping new players in the pathway using quinoxyphen and by studying at the gene and protein level the relationship between AEGEUS and cellular processes that are ultimately linked to its functionality. Knowledge gained from this study will be used to improve our understanding of cell wall signaling. An important ancillary outcome will be knowledge and a small molecule tool that are relevant in leveraging future studies in non-model species in terms of gene orthology and signaling events linked to biotic stress.