Dissecting the Genetic Basis for Seed Coat Mucilage Heteroxylan Biosynthesis in Plantago ovata Using Gamma Irradiation and Infrared Spectroscopy

Matthew R Tucker,Kylie Neumann,Daniel Cozzolino,Michael G Hahn,Neil J Shirley,Jana Phan,Rachel A Burton,Chao Ma

doi:10.3389/fpls.2017.00326

Abstract

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.

Highlights

Xylans are polysaccharides found in plant cell walls and are almost as ubiquitous as cellulose
Much emphasis has been placed on the usefulness of P. ovata as a rich and accessible source of dietary fiber (Pollet et al, 2012; Cappa et al, 2013), little is known about the genetic determinants of seed mucilage formation in this species
The abundance of HX in P. ovata mucilage, which contrasts with pectin-rich Arabidopsis and flax, and its usefulness as a commercial gluten-free dietary fiber supplement make it an attractive model system for xylan research

Summary

Introduction

Xylans are polysaccharides found in plant cell walls and are almost as ubiquitous as cellulose. Considerable effort has been directed toward understanding the mechanism of xylan biosynthesis (York and O’Neill, 2008; Faik, 2010; Rennie and Scheller, 2014), with studies being undertaken in various species including Arabidopsis, rice, poplar, wheat and Plantago (Anders et al, 2012; Chiniquy et al, 2012; Haughn and Western, 2012; Jensen et al, 2013; Lovegrove et al, 2013; Phan et al, 2016). Recently has the Arabidopsis thaliana seed coat mucilage been revealed as an alternative model to study xylan biosynthesis, which may provide new opportunities to investigate key regulatory and biochemical activities (Voiniciuc et al, 2015; Hu et al, 2016; Ralet et al, 2016)

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