HighlightSeed coat mucilage composition and heteroxylan structure varies between different Plantago species and is accompanied by differences in glycosyltransferase family 61 (GT61) copy number and transcript abundance.

Upon exposure to aqueous environments, polysaccharides present in the seed coats of myxospermous species swell and extrude forming a halo of mucilage that completely envelops the seed. The extruded mucilage is usually a composite of pectic, non‐cellulosic, and cellulosic polysaccharides, and because of its accessibility the seed mucilage system has been used extensively in the laboratory to uncover molecular mechanisms associated with plant cell wall (PCW) polysaccharide biosynthesis. The mucilage of Arabidopsis , which is predominantly composed of pectic polysaccharides, is the most extensively characterised. Interrogation of this system has revealed intricate molecular and chemical details about polysaccharide biosynthesis and seed coat development, clearly demonstrating the effectiveness of using seed mucilage systems as a proxy to study PCW polysaccharide biosynthesis. Significant advances have been made in our understanding and identification of the genes and enzymes involved in pectin, cellulose, and xylan biosynthesis. Recent results regarding the composition, combined with the definition of the architectural properties, of extruded seed mucilage are synergistic with our current models of how polysaccharides interact in the PCW. In addition to the desirable characteristics of myxospermy for the study of PCW polysaccharide biosynthesis, industrial applications of seed mucilages are extensive. Strong interest from the food manufacturing and processing, pharmaceutical, cosmetic, and waste management industries has also encouraged researchers to investigate the physiochemical properties of seed mucilages and their possible applications. This article highlights the recent advances made in our understanding of the molecular mechanisms and the architectural properties of mucilage biosynthesis across diverse species.

Seeds from the myxospermous species Plantago ovata release a polysaccharide-rich mucilage upon contact with water. This seed coat derived mucilage is composed predominantly of heteroxylan (HX) and is utilized as a gluten-free dietary fiber supplement to promote human colorectal health. In this study, a gamma-irradiated P. ovata population was generated and screened using histological stains and Fourier Transform Mid Infrared (FTMIR) spectroscopy to identify putative mutants showing defects in seed coat mucilage HX composition and/or structure. FTMIR analysis of dry seed revealed variation in regions of the IR spectra previously linked to xylan structure in Secale cereale (rye). Subsequent absorbance ratio and PCA multivariate analysis identified 22 putative mutant families with differences in the HX IR fingerprint region. Many of these showed distinct changes in the amount and subtle changes in structure of HX after mucilage extrusion, while 20% of the putative HX mutants identified by FTMIR showed no difference in staining patterns of extruded mucilage compared to wild-type. Transcriptional screening analysis of two putative reduced xylan in mucilage (rxm) mutants, rxm1 and rxm3, revealed that changes in HX levels in rxm1 correlate with reduced transcription of known and novel genes associated with xylan synthesis, possibly indicative of specific co-regulatory units within the xylan biosynthetic pathway. These results confirm that FTMIR is a suitable method for identifying putative mutants with altered mucilage HX composition in P. ovata, and therefore forms a resource to identify novel genes involved in xylan biosynthesis.