Abstract

1 - Division of Glycoscience, Department of Chemistry, KTH Royal Institute of Technology, AlbaNova University Centre, 106 91 Stockholm, Sweden; 2 - Umeå Plant Science Centre, Swedish University of Agricultural Sciences, Department of Forest Genetics and Plant Physiology, 901 83 Umeå, Sweden; 3 - Department of Chemistry, Umeå University, 901 87 Umeå, Sweden; 4 - Wallenberg Wood Science Centre (WWSC), KTH Royal Institute of Technology, 100 44 Stockholm, Sweden;

Abstract text: Glucuronoxylan (GX) biosynthesis in the Golgi apparatus involves the substitution of the xylan backbone by 4-O-methyl glucuronic acid (mGlcA) and O-acetyl groups, which play a key role in molecular interaction between cell wall polymers in hardwoods. This study investigates the effect of synthetic (RNAi suppression of GLUCURONIC SUBSTITUTION OF XYLAN1, PtGUX1 genes) and post-synthetic (apoplastic wood-specific expression of fungal GH67--glucuronidase) modification of glucuronidation on GX acetylation, recalcitrance to enzymatic hydrolysis and solubility. Both approaches reduced MeGlcA/Xyl ratio by 30-32% without altering xylan content, while acetyl content was increased only in GUX1RNAi lines. Mass spectrometric analysis revealed that the glucuronidation was reduced in major GX domain containing evenly-spaced mGlcA in Gux1RNAi lines, while GH67 expression lines showed impact on both odd and even substitution patterns. Gux1RNAi lines also showed an increase in xylo-oligosaccharides containing O-2,3 diacetylated Xyl and xylan extractability in subcritical water. None of the transgenic modifications improved Glc or Xyl yields in saccharification without or with acid pretreatments. In conclusion, our study indicates that xylan acetylation is dynamically regulated during biosynthesis and that increased acetylation caused by GUX1 suppression might improve xylan extractability while the achieved level of reduction in glucuronidation did not affect enzymatic saccharification.