All plant cells are surrounded by cell walls, which provide protection from the environment and support during growth and development. Cell walls are important for society because they provide raw materials for energy production (lignocellulosic feedstocks), building materials (wood) and affect food crop yield (resistance against biotic and abiotic stress). Traditionally cell walls have been described as sturdy, solid structures that do not change their composition and structure. Research during recent years has shown that cell walls are actually highly dynamic / plastic structures, which adapt composition and structure in order to meet different functional requirements during development and stress exposure. The plasticity is mediated by the plant cell wall integrity maintenance mechanism, which monitors the functional integrity of cell walls during growth as well as interaction with environment and initiates compensatory responses to maintain integrity. Such a mechanism has been also described in the baker´s yeast, Saccharomyces cerevisiae suggesting that it is a highly conserved mechanism.
The research group is interested in the mode of action of the plant cell wall integrity (CWI) maintenance mechanism and has established a model system to study it´s mode of action. This model system uses Arabidopsis thaliana seedlings for research purposes since they have practical advantages like small size and short generation times in addition to a fully sequenced genome, a large number of molecular tools being available and most importantly the knowledge generated is relevant for other plant species. In order to activate the CWI maintenance mechanism we use a chemical (isoxaben), which inhibits production of cellulose, the major load bearing component of plant cell walls and probably most abundant biopolymer on the planet. If cellulose production is inhibited, cells change their shape because of the high levels of turgor pressure (similar to a car tire) push against a weakened cell wall. Turgor pressure levels can be reduced by adding Osmoticum (sorbitol), therefore preventing shape changes. This is exemplified in the figure below where Arabidopsis seedling roots are treated with isoxaben, osmoticum or combinations thereof. The roots are stained with a reporter for cell shape (green) and cell death (red). The white arrows highlight epidermal cells exhibiting shape changes (magnification).
The picture below provides a high-resolution picture of the epidermal cells exhibiting particularly pronounced turgor sensitive, shape changes (white arrows indicate cells of interest and position within the overview picture).
Another area of interest is the mechanism coordinating plant cell wall metabolism with cell cycle activity. Below are images of seedling root tips where cell walls are stained with a red dye while the activity of a cell cycle gene is indicated by green staining. Inhibition by isoxaben causes also shutdown of gene activity, allowing the research group to study the mechanism responsible.
The scientific publications below provide a more detailed overview of the scientific background.
Selected publications from the group:
Paniagua C., Bilkova A., Jackson P., Dobrowolski S., Riber W., Didi V., Houser J., Gigli Bisceglia N., Wimmerova M, Budínská E., Hamann T. and Jan Hejatko. Dirigent proteins in plants – modulating cell wall metabolism during abiotic and biotic stress exposure. JExBot
Dieuwertje Van der Does, Freddy Boutrot, Timo Engelsdorf, Jack Rhodes, Joseph F. McKenna, Samantha Vernhettes, Iko Koevoets, Nico Tintor, Manikandan Veerabagu, Eva Miedes, Cécile Segonzac, Milena Roux, Alice S. Breda, Christian S. Hardtke, Antonio Molina, Martijn Rep, Christa Testerink, Grégory Mouille, Herman Höfte, Thorsten Hamann and Cyril Zipfel. The Arabidopsis leucine-rich repeat receptor kinase MIK2/LRR-KISS connects cell wall integrity sensing, root growth and response to abiotic and biotic stresses. PLOS Genetics
Hamann T. The plant cell wall integrity maintenance mechanism – Concepts for organization and mode of action. Plant and Cell Physiology, volume 56 (2), 215-223, 2015.
Hamann T. The plant cell wall integrity maintenance – A case study of a cell wall plasmamembrane signaling network. Phytochemistry 112,100-109, 2015.
Engelsdorf T. & Hamann T. “An update on receptor-like kinase involvement in plant cell wall integrity maintenance. Annals of Botany, doi: 10.1093/aob/mcu043, 2014.
Wormit A., Butt S., Chairam I., McKenna J., Nunes-Nesi A., Fernie A. Barter L., Woscholski & Hamann T. “Osmosensitive changes of carbohydrate metabolism in response to cellulose biosynthesis inhibition“ Plant Physiology 159, 105-117, 2012.
Hamann T. “Plant cell wall integrity maintenance as an essential component of biotic stress response mechanisms” Frontiers in Plant Science 3:77, 2012.
Denness, L., McKenna JF., Segonac C., Wormit A., Madhou P., Bennett M., Mansfield J., Zipfel, C. Hamann T. “The plant response to cell wall damage is regulated through interaction of ROS and JA mediated processes”, Plant Physiology 156, 1364-1374, 2011.
Hamann T.*, Bennett M., Mansfield M. & Chris Somerville “Identification of cell wall stress as a hexose-dependent and osmosensitive regulator of plant responses” Plant J. 57(6), 105-26, 2009.* corresponding author