RUI: Cell Wall Associated Kinases As Pectin Receptors

Bowdoin College, Brunswick ME

Investigators

Abstract

All complex organisms are composed of cells that must bind to and communicate with each other, and all cells are surrounded by an extra-cellular matrix that provides some of these abilities. In plants, the extracellular matrix is termed the cell wall, and is partially composed of the carbohydrates cellulose and pectin. Several cell surface proteins act as sensors or receptors for the state of the cell wall, monitoring its integrity and composition. The Wall Associated Kinases (WAKs) are cell surface receptors that bind to the pectin in the cell wall, and regulate cell enlargement. WAKs are also activated by fragmented pectins generated by pathogens, mechanical stress and perhaps by normal developmental changes. The experiments that will be conducted during this project will begin to help in understanding the mechanism by which WAKs can distinguish and respond to different types of pectin in the cell wall, and thereby how plants sense the state of their cell wall, essential for their growth and development. This work will be carried out at a small liberal arts college where the focus is on undergraduate education and research. Students receive a thorough training in experimental science through work in this project, and a significant portion go on to graduate and professional school. The PI also incorporates many aspects of plant cell biology and genetics from his lab into the core cell biology and genetics lab course at the scientist's institution, and is involved in courses for underprepared students in the sciences. The cell walls of angiosperms are composed of a complex arrangement of cellulose, hemicellulose and pectin. The pectins can be selectively and locally modified to be cross-linked into a structural network that can have dramatic effects on cell enlargement. Localized digestion by plant secreted polygalacturonases can also modify the pectin network by loosening the cell wall to permit directional expansion of cells. Numerous pathogens and mechanical disruptions fragment pectin, often leading to a plant stress response. This project involves the Wall Associated Kinases (WAKs) that bind to both long polymers of cross-linked pectin and to pathogen and damage induced pectin fragments, or oligo-galacturonides (OGs). WAKs bound to native polymers are required for normal cell expansion, but bind newly generated OGs with higher affinity, and subsequently activate a distinct stress response pathway. This project will characterize receptor like kinases, cytoplasmic kinases, and potential scaffolding proteins that are phosphorylated upon OG treatment of Arabidopsis. The role of each of the 5 individual WAK isoforms, clustered in one 30 kb locus in Arabidopsis will be genetically dissected using a new CRISPR/Cas9 based WAK deletion mutant. The puzzle is how one receptor type can distinguish and respond in different ways to different types of pectin, during development and the response to environmental disturbance. The goal is to understand if this is achieved through different WAKs each binding different pectins, and in combination with different co-receptors and ligands to activate alternate pathways.