A High Soluble-Fibre Allele in Wheat Encodes a Defective Cell Wall Peroxidase Responsible for Dimerization of Ferulate Moieties on Arabinoxylan

Increasing dietary fibre (DF) intake is an important target to improve health. An attractive strategy for this is to increase DF in wheat which is derived principally from the endosperm cell wall polysaccharide arabinoxylan (AX). The water-extractable form of this (WE-AX) accounts for most soluble dietary fibre (SDF), which is believed to confer particular health benefits. A region of chromosome 6B in some wheat varieties confers high SDF and here we show that the cause is an allele encoding a peroxidase family protein with a single residue change (PER1-v) associated with high WE-AX, compared to the more common form (PER1). Both wheat lines carrying this natural PER1-v variant and those with an induced knockout mutation of PER1 showed reduced dimerization of endosperm ferulate consistent with a mechanism of decreased cross-linking in the cell wall that increases WE-AX. Transiently expressed PER1_RFP fusion protein driven by the native promoter in wheat endosperm was shown to localise to cell walls, whereas PER1-v_RFP did not. We therefore propose that PER1-v lacks the capacity to dimerise AX ferulate in vivo due to mis-localisation caused by the missense single-nucleotide polymorphism (SNP) in the PER1-v allele, so that the SNP acts as a perfect marker. This marker can be used to identify current wheat varieties with high WE-AX to be used by processors and by breeders to ensure future varieties have high WE-AX to make healthier wheat-based foods.