The dynamic cell wall of plant fibers

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The cell wall is one of the most important determinants of plant structure, and also influences many physiological processes including stress and disease resistance, and contributes to the economic value of food, feed, paper, timber, textiles, biofuels and other industrial materials. The cell wall is a dynamic structure, the synthesis and maintenance of which requires activity of thousands of genes, including many related to a complex polymer known as pectin. The function of most genes expressed during cell wall development genes remains unclear. This is true especially for the specialized G-type (gelatinous type) cell walls produced by cells with high tensile strength, such as tension wood and some types of phloem fibers (e.g. bast fibers of flax (linseed, Linum usitatissimum)). Better understanding of the process of fiber development and G-type cell wall deposition will answer basic questions that are relevant to many species of plants and that will also improve understanding of cell wall biogenesis in general. Because our research is being conducted in a major Canadian crop, the outcomes will have direct economic relevance as well. My laboratory has developed extensive genetic and genomic resources for flax, including a whole genome sequence assembly, gene expression profiles, and now a unique reverse genetics population in an elite linseed variety. This population was created using standard chemical mutagenesis, and is therefore not transgenic. Many individuals from this mutant population have now had the gene-rich regions of their genomes sequenced. This has produced a catalog of indexed mutations that allows us to rapidly isolate mutants of almost any gene of interest. This collection is therefore a unique and powerful resource that will allow us to conduct basic research to discover the function of cell wall related genes while simultaneously developing novel genotypes with industrial relevance. I propose to use our indexed mutant population to investigate the role of pectin remodeling enzymes (pectin methylesterases and their associated inhibitors (PME/PMEIs), pectin acetylesterases (PAEs), pectate lyases (PLs), and polygalacturonases (PGs)) in fiber and cell wall development. These each represent medium to large gene families, and we have already identified strong, fiber specific candidates within some of these families. Although each of these types of enzymes is hypothesized to affect G-type cell wall development (based on gene expression studies and models of wall development), their functions in this context have not been investigated genetically or in living plants. Moreover, the activity of these enzymes is expected to greatly influence fiber extractability, which is a key limitation on Canadian flax utilization. We will conduct detailed phenotypic analysis of mutants of pectin-modifying genes of flax using a range of techniques and methods already established in my laboratory, including: (i) comparative genomics and phylogenetics; (ii) microscopy (transmitted light, immunohistochemistry, TEM); (iii) biochemistry (GC/MS, enzyme assays) and spectroscopy (FTIR); (iv) micromechanical testing. With collaborators we will also measure crystallinity, and microfibrilar angle. The outcomes will include novel germplasm that can be immediately transferred to collaborating breeding programs to convert the straw of Canadian linseed from an undesirable waste product to a valuable feedstock in support of nascent industries (e.g. composite materials manufacturing). Most importantly, we will significantly increase understanding of the ways in which plant cell walls can dynamically alter their chemical and physical properties through enzymatic remodelling of pectin.