AUTHOR=Rancour David M. , Hatfield Ronald D. , Marita Jane M. , Rohr Nicholas A. , Schmitz Robert J. 

TITLE=Cell wall composition and digestibility alterations in Brachypodium distachyon achieved through reduced expression of the UDP-arabinopyranose mutase

JOURNAL=Frontiers in Plant Science

VOLUME=6

YEAR=2015

URL=https://www.frontiersin.org/journals/plant-science/articles/10.3389/fpls.2015.00446

DOI=10.3389/fpls.2015.00446

ISSN=1664-462X

ABSTRACT=<p>Nucleotide-activated sugars are essential substrates for plant cell-wall carbohydrate-polymer biosynthesis. The most prevalent grass cell wall (CW) sugars are glucose (Glc), xylose (Xyl), and arabinose (Ara). These sugars are biosynthetically related via the UDP–sugar interconversion pathway. We sought to target and generate UDP–sugar interconversion pathway transgenic <italic>Brachypodium distachyon</italic> lines resulting in CW carbohydrate composition changes with improved digestibility and normal plant stature. Both RNAi-mediated gene-suppression and constitutive gene-expression approaches were performed. CWs from 336 T<sub>0</sub> transgenic plants with normal appearance were screened for complete carbohydrate composition. RNAi mutants of <italic>BdRGP1</italic>, a UDP-arabinopyranose mutase, resulted in large alterations in CW carbohydrate composition with significant decreases in CW Ara content but with minimal change in plant stature. Five independent <italic>RNAi-RGP1</italic> T<sub>1</sub> plant lines were used for in-depth analysis of plant CWs. Real-time PCR analysis indicated that gene expression levels for <italic>BdRGP1</italic>, <italic>BdRGP2</italic>, and <italic>BdRGP3</italic> were reduced in <italic>RNAi-RGP1</italic> plants to 15–20% of controls. CW Ara content was reduced by 23–51% of control levels. No alterations in CW Xyl and Glc content were observed. Corresponding decreases in CW ferulic acid (FA) and ferulic acid-dimers (FA-dimers) were observed. Additionally, CW <italic>p</italic>-coumarates (<italic>p</italic>CA) were decreased. We demonstrate the CW <italic>p</italic>CA decrease corresponds to Ara-coupled <italic>p</italic>CA. Xylanase-mediated digestibility of <italic>RNAi-RGP1 Brachypodium</italic> CWs resulted in a near twofold increase of released total carbohydrate. However, cellulolytic hydrolysis of CW material was inhibited in leaves of <italic>RNAi-RGP1</italic> mutants. Our results indicate that targeted manipulation of UDP–sugar biosynthesis can result in biomass with substantially altered compositions and highlights the complex effect CW composition has on digestibility.</p>