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ARS Home » Midwest Area » Madison, Wisconsin » U.S. Dairy Forage Research Center » Cell Wall Biology and Utilization Research » Research » Publications at this Location » Publication #317486
Title: Cell wall composition and digestibility alterations in Brachypodium distachyon acheived through reduced expression of the UDP-arabinopyranose mutase

Author
item Rancour, David
item Hatfield, Ronald
item Marita, Jane
item ROHR, NICHOLAS - University Of Georgia
item SCHMITZ, ROBERT - University Of Georgia

Submitted to: American Society of Plant Biologists Annual Meeting
Publication Type: Abstract Only
Publication Acceptance Date: 6/5/2015
Publication Date: N/A
Citation: N/A

Interpretive Summary:

Technical Abstract: Plant cell-wall polysaccharide biosynthesis requires nucleotide-activated sugars. The prominent grass cell wall sugars, glucose (Glc), xylose (Xyl), and arabinose (Ara), are biosynthetically related via the UDP-sugar interconversion pathway. RNA-seq analysis of Brachypodium distachyon UDP-sugar interconversion pathway- encoding genes indicates high gene expression in aerial organs with active cell wall biosynthesis. We sought to generate UDP-sugar interconversion pathway transgenic Brachypodium lines, resulting in cell wall carbohydrate composition changes with improved digestibility while maintaining normal plant stature. Both RNAi-mediated gene-suppression and constitutive gene-expression approaches were performed. Cell walls from 336 T0 transgenic plants with normal appearance were screened for complete carbohydrate composition. RNAi mutants of BdRGP1, a UDP-arabinopyranose mutase, resulted in significant decreases in cell wall Ara content, but with minimal change in plant stature. Five independent RNAi-RGP1 T1 plant lines were used for in-depth analysis of plant cell walls. Real-time PCR analysis indicated that gene expression levels for BdRGP1, BdRGP2, and BdRGP3 were reduced in RNAi-RGP1 plants to 15-20% of controls. Cell wall Ara content was reduced by 23-51% of control levels, but no changes in Xyl and Glc content were observed. Corresponding decreases in cell wall ferulic acid (FA), ferulic acid-dimers (FA-dimers), and cell wall p-coumarates (pCA) were observed. We demonstrated that the cell wall pCA decrease corresponds to Ara-coupled pCA. Xylanase-mediated digestibility of RNAi-RGP1 Brachypodium cell walls resulted in a near twofold increase of released total carbohydrate. However, cellulolytic hydrolysis of cell wall material was inhibited in leaves of RNAi-RGP1 mutants. Our results indicated that targeted manipulation of UDP-sugar biosynthesis can result in biomass with substantially altered compositions, but highlighted the complex effect that cell wall composition can have on digestibility.