Extensive Natural Variation in Arabidopsis Seed Mucilage Structure

Abstract

Hydrated Arabidopsis thaliana seeds are coated by a gelatinous layer called mucilage, which is mainly composed of cell wall polysaccharides. Since mucilage is rich in pectin, its architecture can be visualized with the ruthenium red (RR) dye. We screened the seeds of around 280 Arabidopsis natural accessions for variation in mucilage structure, and identified a large number of novel variants that differed from the Col-0 wild-type. Most of the accessions released smaller RR-stained capsules compared to the Col-0 reference. By biochemically characterizing the phenotypes of 25 of these accessions in greater detail, we discovered that distinct changes in polysaccharide structure resulted in gelatinous coatings with a deceptively similar appearance. Monosaccharide composition analysis of total mucilage extracts revealed a remarkable variation (from 50 to 200% of Col-0 levels) in the content of galactose and mannose, which are important subunits of heteromannan. In addition, most of the natural variants had altered Pontamine Fast Scarlet 4B staining of cellulose and significantly reduced birefringence of crystalline structures. This indicates that the production or organization of cellulose may be affected by the presence of different amounts of hemicellulose. Although, the accessions described in this study were primarily collected from Western Europe, they form five different phenotypic classes based on the combined results of our experiments. This suggests that polymorphisms at multiple loci are likely responsible for the observed mucilage structure. The transcription of MUCILAGE-RELATED10 (MUCI10), which encodes a key enzyme for galactoglucomannan synthesis, was severely reduced in multiple variants that phenocopied the muci10-1 insertion mutant. Although, we could not pinpoint any causal polymorphisms in this gene, constitutive expression of fluorescently-tagged MUCI10 proteins complemented the mucilage defects of a muci10-like accession. This leads us to hypothesize that some accessions might disrupt a transcriptional regulator of MUCI10. Therefore, this collection of publicly-available variants should provide insight into plant cell wall organization and facilitate the discovery of genes that regulate polysaccharide biosynthesis.

Cytological Approaches Combined With Chemical Analysis Reveals the Layered Nature of Flax Mucilage

“…Recently described as a new model for the study of carbohydrate metabolism and cell wall properties (Arsovski et al, 2010; Haughn and Western, 2012; Francoz et al, 2015), seed coat mucilage research and its applications for commercial use, like in foaming agents, pet food product design or fabrication of nanofibers (Nybroe et al, 2016; Hadad and Goli, 2018; Kaur et al, 2018), are in part hampered by the fact that the relationships between the mucilage secretory cell (MSC) internal organization, the mucilage chemical composition and the events leading to its extrusion are poorly known. Functional analysis of mucilage biosynthesis and extrusion process are mainly focused on Arabidopsis mutants at the expense of other under-exploited genetic resources such as natural variants and other species like Plantago (North et al, 2014; Phan et al, 2016; Voiniciuc et al, 2016). The large size of the flax MSC, the growing number of studies on flax mucilage polysaccharide composition and its high industrial applications in various industries (Bhatty, 1993; Westscott and Muir, 2003; Alix et al, 2008; Choudhary and Pawar, 2014; Shim et al, 2014) make the flax seed coat mucilage an attractive model to be investigated.…”

Differences in glycosyltransferase family 61 accompany variation in seed coat mucilage composition inPlantagospp.

“…In addition, seed mucilage composition varies considerably across different genera. Arabidopsis is a well-documented myxospermous species that produces seed mucilage rich in rhamnogalacturonan I with smaller amounts of homogalacturonan, cellulose, xyloglucan, xylan, arabinan and galactan (Haughn and Western, 2012; Voiniciuc et al , 2015 b , 2016; Hu et al , 2016). Flax ( Linum usitatissimum ) produces mucilage containing rhamnogalacturonan I and arabinoxylan (Naran et al , 2008), while pysllium ( Plantago ovata ) mucilage is predominantly composed of a complex heteroxylan (Fischer et al , 2004; Saghir et al , 2008).…”

Monitoring Polysaccharide Dynamics in the Plant Cell Wall

“…1F; Table II) or visualized quickly with RR (Table II), a dye that selectively binds to negatively charged molecules such as unesterified GalA regions and is compatible with both light and electron microscopy (Hanke and Northcote, 1975). The RR dye was a convenient probe for identifying chemically mutagenized Arabidopsis mucilage-modified mutants (Western et al, 2001) and a large number of natural Arabidopsis variants with altered mucilage architecture (Voiniciuc et al, 2016). The presence of Ca 2+ ions, which can be manipulated by distinct chemical treatments, negatively regulates the size of RR-stained mucilage capsules.…”