Overexpression of a BAHD Acyltransferase, OsAt10, Alters Rice Cell Wall Hydroxycinnamic Acid Content and Saccharification

Laura E Bartley,Peter I Benke,Gynheung An,Berit Ebert,Peijian Cao,Jizhong Zhou,Steven B Foster,Carsten Rautengarten,Patrick E Canlas,Rolf E Jentoff,Robert Sykes,Fan Lin,Angela Ziebell,Lingfang Gao,Matthew L Peck,Xiaohan Zhang,Jay D Keasling,Susan Brewer,Chithra Manisseri,Pamela C Ronald,Henrik Vibe Scheller ,Miguel E Vega‐Sánchez ,Sung Ryul Kim ,Dawn Chiniquy ,W L Smith

doi:10.1104/pp.112.208694

Abstract

Grass cell wall properties influence food, feed, and biofuel feedstock usage efficiency. The glucuronoarabinoxylan of grass cell walls is esterified with the phenylpropanoid-derived hydroxycinnamic acids ferulic acid (FA) and para-coumaric acid (p-CA). Feruloyl esters undergo oxidative coupling with neighboring phenylpropanoids on glucuronoarabinoxylan and lignin. Examination of rice (Oryza sativa) mutants in a grass-expanded and -diverged clade of BAHD acyl-coenzyme A-utilizing transferases identified four mutants with altered cell wall FA or p-CA contents. Here, we report on the effects of overexpressing one of these genes, OsAt10 (LOC_Os06g39390), in rice. An activation-tagged line, OsAT10-D1, shows a 60% reduction in matrix polysaccharide-bound FA and an approximately 300% increase in p-CA in young leaf tissue but no discernible phenotypic alterations in vegetative development, lignin content, or lignin composition. Two additional independent OsAt10 overexpression lines show similar changes in FA and p-CA content. Cell wall fractionation and liquid chromatography-mass spectrometry experiments isolate the cell wall alterations in the mutant to ester conjugates of a five-carbon sugar with p-CA and FA. These results suggest that OsAT10 is a p-coumaroyl coenzyme A transferase involved in glucuronoarabinoxylan modification. Biomass from OsAT10-D1 exhibits a 20% to 40% increase in saccharification yield depending on the assay. Thus, OsAt10 is an attractive target for improving grass cell wall quality for fuel and animal feed.

Highlights

Grass cell wall properties influence food, feed, and biofuel feedstock usage efficiency
To refine the hypothesis that these enzymes might be involved in grass-diverged cell wall synthesis, we systematically characterized the distribution of this clade in selected plant species and compared the clade with other characterized BAHD proteins
While we are aware that recent analyses have included the presence of a strict HXXXD motif as indicative of whether the protein is an active BAHD (Banks et al, 2011; Tuominen et al, 2011), we have included proteins with single amino acid alterations to this motif, since one of the known biochemically active proteins for the family involved in taxol biosynthesis, BAPT (National Center for Biotechnology Information identifier AAL92459; Walker et al, 2002), possesses a variation of this motif in which the His is replaced by a Ser

Summary

Introduction

Grass cell wall properties influence food, feed, and biofuel feedstock usage efficiency. Examination of rice (Oryza sativa) mutants in a grass-expanded and -diverged clade of BAHD acyl-coenzyme A-utilizing transferases identified four mutants with altered cell wall FA or p-CA contents. Cell wall fractionation and liquid chromatography-mass spectrometry experiments isolate the cell wall alterations in the mutant to ester conjugates of a fivecarbon sugar with p-CA and FA. These results suggest that OsAT10 is a p-coumaroyl coenzyme A transferase involved in glucuronoarabinoxylan modification. Grasslands, including those converted to produce the major cereal crops, rice (Oryza sativa), wheat (Triticum aestivum), and maize (Zea mays), cover 20% of terrestrial land (Kellogg, 2001). Grass root and leaf litter compositions affect soil carbon storage (Pendall et al, 2011; Zhou et al, 2012)

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