Using Plantago ovata As a Model System to Unravel the Molecular Basis of Xylan Biosynthesis

Xylans are one of the most prominent non-cellulosic cell wall polysaccharides in plants and yet their synthesis and assembly remains poorly understood. They are one of the major dietary fibres consumed by humans, our major source of xylan comes from wheat, and upon regular consumption xylans confer positive health benefits through their fermentation by microbiota present in the colon. The heteroxylan polysaccharides are characterised by a backbone of 1,4-B-xylosyl units, where heterogeneity arises from the combinations of monosaccharide substitutions attached to the central backbone. Enzymes from the glycosyl transferase family catalyse the specific glycosyl linkages between each monosaccharide moiety.

This study aims to identify genes involved in heteroxylan biosynthesis using a forward genetics approach and the relatively novel model system Plantago ovata, commonly referred to as psyllium. P. ovata seeds are myxospermous; when seeds are imbibed in an aqueous solution, a polysaccharide-rich layer of mucilage is extruded from the seed coat. This seed mucilage is predominantly composed of heteroxylan that has similar glycosyl linkages to that of wheat arbainoxylan. A mutant population of P. ovata has been established using gamma-irradiation and two mutants, fugitive and hikikomori, with altered heteroxylan phenotypes have been identified. Physical and chemical characterisation of the two mutants indicates differences in polysaccharide structure, amount and composition, and RNA-sequencing analysis of data obtained from the mucilage-producing tissue, is revealing possible candidate genes that may affect xylan biosynthesis.