BBMB Faculty Candidate Seminar

May 9, 2007
1414 Molecular Biology Buidling
4:10 p.m.

Dr. Christoph Ringli
Institute of Plant Biology at the University of Zurich

The role of LRX proteins during cell wall formation

The plant cell wall is a complex structure consisting of the polysaccharides cellulose, hemicellulose, and pectin, and a number of structural cell wall proteins. While the biosynthesis of the different compounds is quite well understood, little is known about the processes that integrate them into a functional cell wall.

LRX genes encode chimeric, extracellular proteins consisting of an N-terminal LRR (leucine-rich repeat) and a C-terminal extensin domain. In Arabidopsis, LRX1 is specifically expressed in root hairs and lrx1 mutants develop a defective cell wall, resulting in aberrant root hair formation. This points towards a role of LRX proteins during cell wall development. To characterize the process LRX1 is involved in, rol (repressor of lrx1) mutants were identified that are able to suppress the lrx1 mutant phenotype. One characterized rol mutant, rol1, is affected in rhamnose biosynthesis and induces a modification in the pectin structure. The finding that a modified pectin structure suppresses the lrx1 mutant phenotype suggests that LRX1 might have a function during pectin matrix formation.

The C-terminal domain of LRX1 is a typical extensin domain, characterized by a repetitive amino acid sequence containing the motif [Ser-Hyp4]n. Extensin proteins are well described and are known to crosslink in the walls of tissue under tensile stress. How the crosslinking of extensins takes place and which amino acid motifs are important for this process in muro is still not well understood. We are using the complementation of the lrx1 mutant with different LRX1 deletion constructs to identify domains and motifs that are crucial for the function of this extensin domain.